ELECTRIC.
Telegraph, from τράλε and γράφω, an instrument to write at a distance. But the term has been from the beginning, and is constantly still applied to apparatus for communicating intelligence to a distance in unwritten signs, interpretable by an intelligent being from their effects perceived through his senses of sight or of sound, and has, in fact, only recently had application to those wonderful combinations of inanimate matter which literally write at a distance the intelligence committed to them. We may, therefore, define telegraphic communication simply as the interchange of ideas between two intelligent beings by means of inanimate matter occupying space between them. Whether men first interchanged ideas by speech or by visible signs, whether spoken language was given complete by the Creator to the first two human beings, or was gradually invented by them and their successors, are questions upon which revelation and history shed but partial light; and the origin of the telegraphic art is shrouded in obscurity. The chief object of the present article being to explain the principles and practice of the Electric Telegraph, our space does not allow us to enter on the history of language or of other systems of signalling by sound, of dumb signs, of lamp-signals as proposed by the Greek general, Eneas, and improved by Polybius, of flag-signals as universally practised at sea for communicating between ship and ship, of the semaphore as used by various governments until the realisation of the electric telegraph; or even to more than cursorily allude to the successive suggestions and inventions through which the electric telegraph itself has risen to its present important position among the various material means which the ingenuity of man has made subservient to his moral and intellectual wants. We shall only further allude to those other telegraphic systems which have been mentioned, for the sake of illustrating the general principles of signalling, which will form the subject of our first section.
I.—MATERIAL SIGNS OF IDEAS.
A signal is a change in the condition of external matter produced by one intelligent being with the intention that it should be perceived by another. A word is the direct and explicit expression of an idea, according to a pre-arranged plan of signalling, and may be communicated by voice, by trumpet calls, by gun fire, by gesture or dumb signs, by lamp-signals, by flags, by semaphore, or by electric telegraph. The simplest system of word-signalling hitherto practised, is that of the nautical flag telegraph, in which each hoist represents a word by a combination of four flags in four distinct positions. If \( n \) denote the number of different varieties of flag out of which the four to be sent up may be selected, the number of different ideas which can be expressed by a single hoist is \( n^4 \), since there are \( n \) varieties out of which the flag for each of the four positions may be independently chosen. To commit to memory each of so great a number of combinations, which will amount to 456,976 if \( n = 26 \), would be a vain effort, and hence the operators on each side must have constant recourse to a dictionary, or code as it is called, arranged in two parts, one showing the combinations of flags to express each word included in the list, and the other the word expressed by each combination of flags. For the sake of convenient reference, each flag is called by the name of a letter of the alphabet, and all that must be borne in mind by the operator is the letter by which each flag is thus designated. Sometimes the words to be expressed are spelled out by means of these letters as in ordinary language; but as in most words there are more than four letters, as scarcely any two consecutive words are spelled with four or less than four letters, and as more than four flags at a time cannot be conveniently used, the system of alphabetic signalling frequently requires the use of two hoists for a word, and scarcely ever has the advantage of expressing two words by one hoist. It is, therefore, much more tedious than code signalling in the nautical telegraph.
In point of simplicity, spoken words may be considered as almost on a par with the nautical telegraph, since each word is in reality spoken and heard almost as a single utterance. Next to these in order comes the system of spelling out words letter by letter in succession, in which—instead of, as in the nautical telegraph, merely 456,976 single symbols to express the same number of ideas—26 distinct symbols are used to express by their combinations any number whatever of distinct ideas. Next again to this may be considered the system by which several distinct successive signals are used to express a letter; and letters thus communicated by compound signals are combined according to the ordinary method of language to spell out words. It is to this last class that nearly all systems of electro-telegraphic signalling hitherto carried out in actual practice belong. But some of the earliest and latest proposals for electric telegraphs are founded on the idea of making a single signal to represent a single letter of the alphabet: as for instance, Ampère's suggestion of 1821, put in practice before the Society of Arts in Edinburgh, by Mr Alexander in 1837, in which a distinct conducting wire was used for each letter of the alphabet; also, a method of signalling by currents of different strengths for the different letters of the alphabet, tried and found successful through the Atlantic cable in harbour at Devonport in 1858, by the writer of this article; and the newest American printing telegraph, Mr Hughes's very successful instrument, which shows each letter by the measurement of a simple duration of time.
We shall now proceed to examine the nature of simple electric signals, and the modes of representing letters by means of them, taken either singly or in combinations, which have been adopted in the various practical systems hitherto adopted; and we commence with a slight preliminary notice of elementary laws of electric action and electrical properties of matter, with which we have to deal as the material means employed in the communication of ideas by the electric telegraph.
II.—ELECTRICAL DEFINITIONS AND EXPLANATIONS.
(1.) Electro-motive Force, Conduction, and Insulation.—Electricity tends always to place itself so as to exercise no force in the interior of any matter upon which it may be situated, or to do away with all electric force, should there be independent distributions of electricity in the neighbourhood of the body considered. This tendency gives rise to what is called electro-motive force, and is always more or less resisted in every kind of matter. In one large class of bodies, however, including metals, the resistance to electro-motive force is so extremely slight, that it is altogether undiscoverable without tests of a very special kind, or with-
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1 See Rollin's Ancient History, book xviii. sec. 6. Electrical out the use of excessively copious sources of electricity; and the class of bodies thus characterised are accordingly called conductors. On the other hand, many bodies oppose to the natural electric tendency so great a resistance that electricity may be placed in any manner upon or in them, and will be found to remain in the positions assigned to it, without any sensible change for finite perceptible intervals of time, for seconds, for minutes, for days, weeks, or years. Such bodies are called non-conductors or insulators of electricity. But while no kind of matter, as has been stated, is found to be perfectly devoid of electrical resistance, neither does any kind of matter perfectly and absolutely prevent all motion of electricity through it. It appears, therefore, that the distinction between conductors and non-conductors or insulators, is not an absolute distinction, but a distinction of degree. Bodies which possess the resisting quality to a very high degree, such as glass, vulcanite, india-rubber, gutta-percha, dry silk, and nearly all vegetable and animal substances, when deprived of their natural moisture by heat not sufficient to cause decomposition, are commonly called insulators or non-conductors. Bodies which exercise but very little resistance to electric locomotion, such as metals, charcoal, acid and saline solutions, and watery liquids generally, or moist porous solids, are commonly called conductors. There are, in fact, very large differences in degree of resistance presented by different bodies of either one class or of the other. Thus, the writer has found, that a Leyden phial charged and hermetically sealed, and after that kept cool, will not allow as much electricity to flow through it in three years as will flow in a few minutes through a piece of gutta-percha, similarly dealt with. Hence, the resistance of cold glass may be as many times the resistance of gutta-percha as there are of minutes in a year. As wide differences exist between the resisting qualities of different bodies, called conductors. Thus, a piece of damp wood or thread may be used to discharge a Leyden phial gradually in the course of a few minutes; a metallic wire of equal dimensions and similar form may effect a discharge in the millionth of a second or less.
The testings of the first Atlantic cable made during the spring of 1857, when it was in process of manufacture, afforded data "not sufficient for any very accurate determination, yet definite enough to show the resistance of the gutta-percha of that cable at temperatures between 60° and 90° Fahr. to be from one hundred million million million to twenty million million million times that of copper, when equal and similar volumes of the two substances are compared." Mr F. Jenkin has since, by experiments of a very precise character, on the Red Sea and various Indian cables, at the works of Messrs Newall and Company, Birkenhead, found the resistance of the insulating medium of the Red Sea cable at temperature 60°, after electrification for one minute, to be one hundred and four million million million times that of an equal and similar volume of copper of the best quality measured by Weber. Thus the numbers $1, 100 \times 10^{9}$, and $50 \times 10^{11}$ may be taken as expressing relatively the resisting powers of copper, gutta-percha, and glass, at a common atmospheric temperature, or rather of particular specimens or qualities of those substances, since large differences are found in the resistances of different specimens, probably attributable to differences, which may be excessively slight, in their chemical composition.
A conductor supported by a non-conductor is said to be insulated.
III.—GENERAL DESCRIPTION OF ELECTRIC TELEGRAPHS FOR LAND AND SEA.
The first requisite for electro-telegraphic communication between two localities, is an insulated conductor extending from one to the other. This, with proper apparatus for originating electric currents at one end, and for discovering the effects produced by them at the other end, constitutes an electric telegraph. Faraday's term "electrode," literally a way for electricity to travel along, might be well applied to designate the insulated conductor, along which the electric messenger is despatched to bear tidings to the distant intelligence. It is, however, more commonly and familiarly called "the wire," or "the line."
The apparatus for generating the electric action at one end is commonly called the transmitting apparatus, the transmitting instrument, or the sending apparatus or instrument, or sometimes simply the sender. The apparatus used at the other end of the line to render the effects of this action perceptible to any of the senses—eye, ear, or taste (all have been used in actual telegraphic signalling)—is called the receiving apparatus or instrument. In land telegraphs, the main electrode consists generally of a "galvanized" iron wire stretched through the air from pole to pole, at a sufficient height above the ground for security. The supports or insulators, as they are called, by means of which it is attached to the poles, are of very different form and arrangement in different telegraphs, but involve essentially a stem of glass, porcelain, coarse earthenware, or other non-conducting substance, protected by an overhanging screen or roof from falling rain. One end of this stem is firmly attached to the pole, and the other bears the wire. The best idea of a single telegraphic insulator will be formed, by considering a common umbrella, with its stem of insulating substance, attached upright to the top of a pole, and bearing the wire supported in a notch on the top outside. The umbrella may be either of one substance with the stem—all glass, or all glazed earthenware for instance—or may be of a stronger material, such as iron, with an insulating stem fitted to it to support it below. The best insulators undoubtedly are those of continuous glass; but well glazed earthenware, which is cheaper, and insulates well as long as the glazing is sufficient to prevent the porous substance within from absorbing moisture, may be used with economical advantage in some cases.
The following figure represents a form of glass insulator applied to nearly all the wires of the British and Irish Magnetic Telegraph Company, by their engineer, Sir Charles Bright, which has proved very satisfactory.
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1 In the month of February or March 1857, a number of glass balls, with tubes sealed to apertures in them, so as to constitute long-necked phials, were each partially filled with water, which moistened the whole inner surface of the globe and neck, making as it were the inner coating of the Leyden phial. The outside of the globes were coated with tinfoil, and each was charged as a Leyden phial, and hermetically sealed. After about two years, one was opened, and was found still strongly charged. In February of the present year two more were opened, of which one showed no electric indications, but the other was found strongly charged, showing an electrometric indication (difference of potentials between inside and outside coatings) equal to that of about 420 elements of Daniell's battery.
2 Lecture "On the Atlantic Telegraph" before the British Association, Dublin, 1857, by Prof. W. Thomson.
3 For a more comprehensive statement of his results, see below, sect. iv.
4 The writer has found that Leyden jars made of thin glass shades will, if of flint glass, keep their charges for weeks in as large proportion as they will for hours if of common glass. The latter quality is nearly, if not quite, as clear as the former, being only distinguishable by a slight tinge of green when seen in mass; and being now made very thin, and so quite satisfactory in point of transparency, is the more commonly used for protecting ornamental objects. It is produced at about half price, weight for weight.
That is to say, coated with zinc to prevent corrosion. In all submarine telegraphs hitherto made, the conductor is of copper, either a solid wire, as in the earlier lines, or a little rope or "strand" laid together spirally, as first proposed by the writer of this article at a meeting of the Philosophical Society of Glasgow, Nov. 29, 1854, and since universally adopted, for the purpose of allowing a sufficiently massive conductor to be used to diminish inductive embarrassment, and ensure a rapid rate of signalling through submarine lines of great length.
This conductor is insulated by a continuous coating of gutta-percha enclosing it. A layer of tarred yarn, forming round the gutta-percha a soft, tough bed, and strong iron wires, laid firmly, and close to one another, round it in spirals but slightly inclined to the longitudinal direction, are added for protecting the gutta-percha from external injury, and complete what is called an electric cable. This iron sheath ought to be extremely strong in cables to lie in shallow water or rocky bottoms, in situations exposed to the disturbing influence of waves or currents, or to accidental rough usage from ships' anchors or otherwise. On the other hand, for cables to lie on a soft bottom, under very deep water, the iron sheath need not be stronger than to afford the necessary protection to the copper and gutta-percha during the process of submergence, the extremely tranquil condition of the great ocean depths in most localities affording complete immunity, both from continued wear and tear and from accidental damages, to an electric cable once submerged in good condition.
In some submarine cables, several separately insulated conductors are enclosed in a common iron sheath, for the sake of economy; but as each is separately insulated in its own gutta-percha, and as each gutta-percha coating is separately sheathed in tarred yarn, which under sea-water becomes thoroughly moist, and keeps the outer cylindrical surface of the gutta-percha round each wire at the earth's electric potential, we may regard such an arrangement as equivalent, in electrical circumstances, to so many independent electric cables laid side by side. It will be a question whether any kind of mutual influence can sensibly affect the electric action through a number of conductors so placed. It cannot be overlooked that in reality there is an effect produced by electro-magnetic induction (one of Faraday's first electrical discoveries), according to which the rising or falling of a current through one of the conductors must give rise to currents, respectively in the similar ones, and in contrary directions in the others; but it has been theoretically demonstrated by the writer, that this influence is so small in an extended cable as to be insensible, in ordinary telegraphic work, through any considerable length of wire.
IV.—QUALITIES OF A LINE OF TELEGRAPH.
The efficiency of the telegraph depends on three qualities of the main electrode—
(1) Its Conducting Power. (2) Its Insulation. (3) Its Electrostatic Capacity.
We shall proceed to explain in order the general character of each of these qualities.
(1) Conducting Power.—The conducting power of a wire, or other elongated portion of matter, is measured by the quantity of electricity which it allows to flow through it, when a stated "electromotive force," or "difference of electric potentials," is maintained between its two ends.
The word "power" here may be regarded as used in a somewhat figurative sense, since in reality we cannot regard the conductor as exercising itself a power in the transmission of electricity through it, and must rather conceive it as admitting electricity to pass with more or less of resistance when urged by an external source of power. Hence the quality with which we are concerned may be more naturally, and is in point of fact more generally, expressed in terms of the resistance to transmission, regarded as a quality inverse to that of conducting power, and expressed numerically by the reciprocal of the measure of the conducting power. An independent explanation and definition of the electrical resistance of a conductor may be given as follows.—The electrical resistance of a conductor is measured by the amount of electromotive force, or of the difference of potentials which must be maintained between its ends, to produce a stated strength of electric current through it. To render these statements completely definite, we must now consider what standards are to be adopted for the measurement of electromotive forces, and of quantities of electricity. In this branch of electrical science, we are necessarily as yet somewhat embarrassed by the variety of electrical effects, among which we have to choose that which is most suitable for measuring the amount of the agency which we regard as their cause. Thus, to measure the strength of a current, we may use a galvanometer, in which the directing power which a wire conveying electricity exerts on a magnetic needle in its neighbourhood, according to Oersted's great discovery, is the object of measurement. Many different forms of this instrument have been invented and extensively used, each having the property of giving at every instant a measure of the rate at which electricity is flowing through the conductor to be tested. Again, the amount of chemical decomposition effected by an electric current may, according to Faraday's law of definite electro-chemical action, be used to measure the integral amount of current which has passed in any finite interval of time. The difficulty of obtaining definite absolute measurements, by means of the galvanometer, has led many experimenters to adopt this electrolytic method of gauging an electric current. Although subject to many drawbacks, which would render it intolerably inconvenient for ordinary use, it is susceptible of considerable accuracy when carried out with sufficient care, and may be advantageously had recourse to for reducing the indications of an ordinary galvanometer to absolute measure, when an absolute galvanometer is not available. On the other hand, the most elementary method of reckoning electrical quantity—that in which the mutual forces of attraction and repulsion manifested among electrified bodies are the immediate subjects of measurement—has been hitherto but very little used in practice, the total want, until within the present year, of any instrument available as an absolute electrometer, and the unsatisfactory character of almost all ordinary electrometers or electrosopes as to availability, for even relative measurements of an accurate kind, having hitherto proved a barrier.
The elements of these different principles of measurement, separately worked out by the experimenters and mathematicians, to whom our knowledge in the different parts of the subject is due, have been brought together by Professor Weber of Göttingen; and owing to his admirable investigations, we have now a thoroughly complete triple foundation for an electrometric system, in which the numerical relations between the three different classes of natural effects we have mentioned are established, and measurements of electrical quantity, electromotive force, and electrical resistance made by means of any one of them, is immediately reducible to absolute measure in terms of any other. It is scarcely possible to over-estimate the value of this step in science, whether in regard to actual and pro- Qualities of a Line of Telegraph.
Telegraph, Electric.
Qualities of a Line of Telegraph.
We regret that the limits within which this article must be confined prevent us from more than alluding to so important a topic. For information regarding it the reader is referred to Weber, "Messungen galvanischen Leitungswiderstande nach einem absoluten Maasse," Poggendorff's Annalen, March 1851; Thomson, "Mechanical Theory of Electrolysis," "Application of the Principle of Mechanical Effect to the Measurement of Electromotive Force, and of Galvanic Resistances in Absolute Units," and "Transient Electric Currents."—Philosophical Magazine, 1851 and 1852; Weber, "Electrodynamische Maassbestimmungen insbesondere Zurückführung der Stromintensitäts-messungen auf Mechanischen Maas," Leipzig, 1856; Thomson, "On the Electric Conductivity of Commercial Copper," and "Synthetical and Analytical Attempts" on the same subject; "Measurement of the Electrostatic Force between the Poles of a Daniell's Battery, and Measurement of the Electrostatic Force required to produce a Spark in Air,"—Proceedings of Royal Society, 1857 and 1860.
(2) Insulation of a Line of Telegraph.—The true measure of the insulation of a body is the resistance to conduction of its supports. The reciprocal of this, or the conducting power of the supports, measures the defectiveness of the insulation. From the explanations given in Section II., and in the preceding part of the present section, it will be readily understood that perfect insulation is impossible, but that if the supports on which a telegraph wire rests present on each part and on the whole so great a resistance to electric conduction as to allow only a small proportion of the electricity, sent in, in the actual working, at one end to escape by lateral conduction, instead of passing through the line and producing effect at the other end, the insulation is as good as need be for the mode of working adopted. With so good insulation as is attained in a submarine line round every part of which the gutta-percha is free from flaws, no telegraphic operation completed within a second of time can be sensibly influenced by lateral conduction; for a charge communicable to such a wire thus insulated in gutta-percha under water at an ordinary temperature, is so well held that, after 30 seconds, not so much as half of it is found to have escaped, from which, according to the familiar "compound interest" problem, it appears that the loss must be at a rate less than 5 per cent. per two seconds; and hence, the insulation is practically "as good as perfect," unless retention of a charge for several seconds of time is in some way required for the signalling. This cannot be the case except in very long submarine lines, when, owing to the great "electrostatic capacity" of the conductor (which we have next to consider), a very slow rate of signalling is all that can be attained. In all submarine lines of lengths not exceeding 1000 miles, there is no sensible loss of working effect by imperfect insulation, except through decided flaws in the gutta-percha; and even in the 2000 nautical miles of submarine telegraph connecting Ireland with Newfoundland, the loss would be no obstacle to good working, and would be, in fact, inappreciable on the telegraphic signals of the degree of rapidity which would be sent through it, if the gutta-percha were throughout in such condition as any hundred miles of submarine cable found passable by the ordinary tests.
The test for insulation we have indicated, in which a charge is communicated and its rate of dissipation is observed when both ends of the cable are left insulated, is available for every length of submarine cable from a few yards to as many thousand miles, and is extremely easy in practice with the aid of one or other of two forms of elec-
trometer, patented by the writer for this application. It will show faults on short lengths which, when separately tried by the ordinary galvanometric method, might be overlooked, but which, when the different lengths are put together, into one long cable, would tell most seriously on the insulation of the whole; and it is therefore of especial value for testing, in every department of the manufacture, although hitherto it has not been taken advantage of. It has another even more important application—to discriminate between a slight fault of insulation close at hand and a worse fault at a greater distance in a very long submarine cable. Even if the test is to be made on board ship during the submergence of the cable, it can be put in practice with great ease by means of a portable electrometer recently constructed by the writer for the use of travellers in observing atmospheric electricity; or failing a suitable electrometer, a somewhat less direct method of applying the same test, either at sea or on shore, is afforded by the particular mode of using his marine galvanometer in measuring "discharges," introduced by the writer in the submergence of the Atlantic cable.
The ordinary test for insulation consists in applying a galvanic battery, with one pole to earth and the other through a galvanometer coil, to the line of telegraph of which the remote end is kept insulated. If the insulation of the whole line were perfect, the galvanometer needle would stand at zero; but when looked for with a battery of suitable power and a galvanometer of suitable sensibility, indications of a current are always found, unless it is a very short length of very perfectly insulated line that is tested. The absolute measure of the strength of this current divided by the absolute measure of the electromotive force of the battery gives an absolute measure for the insulation of the cable. No telegraphic testing ought in future to be accepted in any department of telegraphic business which has not this definite character, although it is only within the last year that convenient instruments for working in absolute measure have been introduced at all, and the whole system of absolute measurement is still almost unknown to practical electricians.
It has been put in practice systematically for the first time, in August and September 1859, at the works of Messrs R. S. Newall and Co., Birkenhead, in the experiments by Mr F. Jenkin alluded to above. A complete description of this important investigation has been communicated to the Royal Society of London, and will, it is hoped, soon be published in the Transactions. In the meantime, the chief results will be sufficiently understood from the following brief account, for which the writer is indebted to Mr Jenkin:
The resistance of gutta-percha at various temperatures was determined by measuring the rate of loss from three separate knots of insulated wire immersed in water, and kept electrified by a galvanic battery. One knot was covered with pure gutta-percha; the two others with different proportions of Chatterton's compound and gutta-percha. The loss, or current flowing from the metal conductor to earth through the gutta-percha coating, was measured on a very delicate galvanometer; corrections due to varying electromotive force of battery and loss from the connections were made on the result of each experiment. A regular and remarkable decrease in the rate of loss was observed for some minutes after the first application of the battery to the cable. The rate of loss was therefore measured from minute to minute for five minutes with each pole of the battery.
The results of the experiments entered as abscissae and ordinates furnished regular and complete curves between the temperatures of 50° and 80° Fahr., for pure gutta-percha, and between 60° and 75° for the mixed covering. The curves showing the loss through pure gutta-percha were very regular, and were not affected at ordinary temperatures by a change in the sign of the current; the loss increased very rapidly at the higher temperatures. The
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1 For a description and drawing of this instrument see section viii. art. 4, below. 2 The length of a knot, or nautical mile, is taken as 6087 feet. Qualities curves representing the loss through the compound were less regular; some difference was observed in the tests with opposite currents; the extra resistance due to continued electrification was also greater. This extra resistance was most marked in the coil covered with the thickest coat of gutta-percha. Chatterton's compound was found to be the better insulator at high temperatures, but below 65° pure gutta-percha had the advantage.
The absolute resistance, G, of the gutta-percha covering was next obtained from long cables in the same units as those employed to measure the resistance of metal conductors, by comparing the deflection caused by the current traversing a known resistance on one galvanometer, with the deflection caused on a second galvanometer by the current from the same battery flowing through the gutta-percha to earth.
G having been obtained in the proper units from a mean of many experiments at one temperature, the specific resistance, S, was calculated by the following equation given by Professor W. Thomson:
\[ S = \frac{LG}{\log_a} \]
Let \( \frac{a}{b} \) be the ratio of the external to the internal diameter of the covering, and L be the length of the cable in feet, then
\[ S = \frac{LG}{\log_a} \]
The values of S were inferred for various intermediate temperatures by means of the curves previously obtained. The two following tables contain some of the principal results:
**Table I.—Specific resistance in British absolute Units of the Red Sea covering (Chatterton) at various Temperatures.**
| Temperature | Zinc to Cable | Copper to Cable | |-------------|---------------|----------------| | | After Electric | After Electric | | | fication for one | fication for five | | | Minute | Minutes | | 60° | 2152 x 10^7 | 3390 x 10^7 | | 65 | 1810 x | 2947 x | | 70 | 1460 x | 2378 x | | 75 | 1160 x | 1753 x |
**Table II.—Specific resistance, in British absolute Units, of pure Gutta-Percha at various Temperatures.**
| Temperature | Zinc to Cable | Copper to Cable | |-------------|---------------|----------------| | | After Electric | After Electric | | | fication for one | fication for five | | | Minute | Minutes | | 50° | 4113 x 10^7 | 5652 x 10^7 | | 55 | 2917 x | 3830 x | | 60 | 2165 x | 2549 x | | 65 | 1634 x | 1558 x | | 70 | 1162 x | 1291 x | | 75 | 805 x | 877 x | | 80 | 565 x | 613 x |
The importance of having results thus stated in absolute measure is illustrated by the circumstance that the writer has been able at once to compare them, in the manner stated in Section II. above, with his own previous deductions from the testings of the Atlantic cable during its manufacture in 1857, and with Weber's measurements of the specific resistance of copper.
From Mr Jenkin's investigation it appears that the insulating power of the coating of a submarine cable is as nearly as possible equal under positive and negative electrifications, and equally altered by the continuance of one and the other charge. No such symmetry as to positive and negative is found in the case of a faulty cable, either submerged, as is well known among practical electricians, or coiled on land, as has been ascertained by the writer, and we have thus an indication for discriminating between loss by conduction through sound gutta-percha, and loss through flaws, which will probably prove a most valuable test in the manufacture of future cables.
It is to be remarked, that the method of testing insulation by continuous galvanometric measurement of the loss under influence of a constant battery, is the only one applicable to land wires, since, in consequence of the smallness of the electrostatic capacity of a wire stretched in the air from pole to pole, any charge communicated to it would be lost in a few seconds, even if the insulation were as good absolutely as it is in a submarine cable, and is, in fact, lost almost instantly, since, except in weather in which the atmosphere is unusually dry, the loss over even glass umbrella-shaped insulators (of which the surfaces absorb moisture from the air), and moist spider lines between the wire and the poles, is much greater than that experienced through the gutta-percha of a submarine cable, on equal lengths of line, under the influence of equal constant batteries.
(3.) Electro-static Capacities of Telegraphic Conductors.—In 1849, Werner Siemens proved, that "when a current is sent through a submerged cable, a quantity of electricity is retained in charge along the whole surface, being distributed in proportion to the tension of each point" (that is to say, the difference of potentials between the conductor at any point and the earth beside it). In 1854, Faraday showed the effect of this "electrostatic charge" on signals sent through great lengths of submerged wire, bringing to light many admirable phenomena, and pointing out the "inductive" embarrassment to be expected in working through long submarine telegraphs. In letters to Professor Stokes in November and December of the same year, published in the Proceedings of the Royal Society for 1855, Professor W. Thomson gave the mathematical theory of these phenomena, with formulae and diagrams of curves, containing the elements of synthetical investigation for every possible case of practical operations. Our limits prevent us from entering on this subject at all; but the following statement of preliminaries will convey some idea towards its bearing on the working of land and submarine telegraphs.
The conductor of a submarine cable has a very large electrostatic capacity in comparison with that of a land telegraph wire stretched in the air from pole to pole, in consequence of the induction, as of a Leyden phial, which takes place across its gutta-percha coat, between it and its moist outer surface, which may be regarded as perfectly connected with the earth, that is to say, at the same potential as the earth. The mathematical expressions for the absolute electrostatic capacity, c, per unit of length, in the two cases are as follows:
**Submarine Line.** \( D = \) diameter of inner conductor, supposed circular, or of a circle inappreciably less than one circumscribed about the strand, constituting a modern submarine conductor.
\( D = \) outer diameter of insulating coat.
\( I = \) specific inductive capacity of the gutta-percha, or other substance constituting the insulating coat.
\[ C = \frac{I}{D} \log \text{denoting a Napierian logarithm.} \]
**Air Line.**—Single wire of circular section, diameter \( D \), undisturbed by the presence of others, and supported at a
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1 The same formula, except the constant factor, bringing it to absolute electrostatic measure, has been more recently investigated by Mr Werner Siemens and Mr Cromwell F. Varley separately, the latter, by a very remarkable method, involving no other mathematical forms than such as are commonly used in the theory of "compound interest," being in reality the principle more concisely expressed in the language of the integral calculus by the formula \( \int \frac{dx}{x} = \log \frac{A}{x} \). constant height, \( h \), above the earth by poles so far asunder as not to influence its capacity sensibly.
\[ C = \frac{1}{2 \log_4 D} \]
**Example 1.**—Atlantic Telegraph.
\( D' = 4 \) of an inch; \( D = 0.89 \); \( \log \frac{D'}{D} = 1.5 \); \( C = \frac{1}{3} \).
From Faraday's experiments on the specific inductive capacity of glass, shell-lac, and sulphur, it is probable that the value of \( I \) for the gutta-percha of a submarine cable does not differ much from 2, and this estimate is in accordance with all the data from telegraphic operations and experiments which have yet been collated. Hence the most probable estimate we can now make of the capacity of the Atlantic cable is \( \frac{1}{3} \) of a unit per foot; which may be explained, that the capacity of the conductor, in a specimen of the cable 1 foot long, with its sheath connected with the earth, is the same as that of a globe of \( \frac{1}{3} \) of a foot radius, insulated out of reach of disturbing influence.
**Example 2.**—Land line \( \frac{1}{4} \) inch diameter, circular conductor, at a height 20 feet above the ground.
\[ \log \frac{4h}{D} = 8.25; \quad C = \frac{1}{16.5} \]
The capacity, therefore, in this case, is \( \frac{1}{16.5} \)th of that of the Atlantic cable, for the same length.
The bulk of this wire would be rather more than 8 times that of the Atlantic conductor, for equal lengths. If made of iron, its "resistance" might be somewhat less, or possibly as much, or even more; the conductive quality of iron telegraph wires having never yet been thoroughly investigated. We may estimate the "resistance" of the iron wire in question as not improbably being from \( \frac{1}{8} \)ths to \( \frac{1}{4} \)ds of that of equal lengths of the Atlantic conductor. The mathematical theory of submarine signalling enables us to conclude, that in attempting to work through 2000 nautical miles of such a land line as we have supposed, at 27 or 33 words a minute, inductive embarrassment would be experienced equal in absolute amount to that which was actually overcome when the Atlantic cable was worked through between Valencia and Newfoundland at the rate of 2 words a minute. It would obviously be much more difficult to deal with the inductive difficulty at the high speed than at the low; and it is probable that about 20 words would be the highest speed attainable through 2000 nautical miles of land line of iron wire, \( \frac{1}{4} \)th of an inch diameter, insulated at an ordinary distance from the earth. The same degree of true inductive embarrassment would be met with in working
At 80 words per minute through 1000 nautical miles.
- 320 " - 1280 "
As no higher speed than 30 to 50 words a minute has yet been attained through 250 nautical miles of land telegraph, and as 1000 miles are not often worked through direct, and never at any such speed as 80 words a minute, we may infer that the induction of electrostatic charge has never yet been sensible as an obstacle to rapid working through land lines of telegraph.
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1 The induction coils were superseded by Daniell's battery at Valencia, after a few days' trial through the rapidly failing line had seemed to prove them incapable of giving intelligible signals to the Newfoundland station; but, owing to the immediate introduction and continued use of an entirely new kind of receiving instrument—the mirror galvanometer introduced for long submarine telegraphs by the writer—at Valencia, the signals from the Newfoundland coils were found sufficient during the three weeks of successful working of the cable. It is quite certain that, with a properly adjusted mirror galvanometer as receiving instrument at each end, twenty cells of Daniell's battery would have done all the work that was done, and at even a higher speed if worked by a key devised for diminishing inductive embarrassment, according to the indications of the mathematical theory; and the writer, with the knowledge derived from disastrous experience, has now little doubt but that, if such had been the arrangement from the beginning, if no induction coils and no battery power, either positive or exceeding 20 cells of Daniell's negative, had ever been applied to the cable since the landing of its ends, imperfect as it then was, it would be now in full work day and night, with no prospect or probability of failure. for which, except in towns, the best plan is generally a large copper-plate, buried in moist ground or below water. The gas-pipes and water-pipes of towns are often used for "earths," as the conductors leading to the earth are familiarly called.
The number of different kinds of simple signal that can be made depends on the number of different degrees of current that can be produced by the regular operation of the transmitting instrument. An extremely simple system of telegraphing consists of using different degrees of current singly, for the different letters of the alphabet; this, in any case in which it is applicable, will probably give a greater speed of signalling than is attainable through the same line by any other method. There are, indeed, many serious practical difficulties in the way of its application, although none which would be insuperable, if the insulation of the line were either practically "perfect" (see above, Section II.), or nearly constant. This condition as to insulation, is generally violated in air-lines of any considerable length as at present constructed; but it is probably fulfilled in all submarine lines sufficiently free from flaws in their insulating coats to be permanently successful. All things considered, it is far from improbable that the method of signalling by a distinct degree, positive or negative, of received current, for each letter of the alphabet, of which successful trials through lengths from 1500 to 3000 British statute miles of the Atlantic cable, when coiled on board the Agamemnon and Niagara, were made by the writer of this article, both in harbour at Devonport, and at sea on the experimental cruise in the Bay of Biscay, in 1858, may be the most advantageous in all submarine lines exceeding 1500 or 2000 miles of extent. In the methods actually practised through the Atlantic cable during the process of laying, and in the three weeks of its successful working between Valencia and Newfoundland, as well as in all other actual telegraphs as hitherto worked, either three different degrees, or two different degrees, of received current have been utilised for the indication of signals. We have thus the following exhaustive division of practical electro-telegraphic systems.
Class I.—Systems in which three different degrees of received current are distinguished.
Class II.—Systems in which two different degrees of received current are distinguished.
To Class I. belong—1. Cooke and Wheatstone's needle system of 1837, with five wires, and their double-needle instrument working through two-line wires, still to some extent used by the original Electric Telegraph Company; and their single needle instrument, similarly worked, with only one-line wire.
2. Steinheil's telegraph of 1837, indicating electric signals either by visible motions, by sounds, or by marks on a ribband of paper.
3. Highton's system, introduced by the British Telegraph Company, and still much used in their English and Scotch lines, by the British and Irish Magnetic Telegraph Company, with which the first-mentioned company became amalgamated some years ago.
4. Improved double-needle instrument, to work through one line, with simplified key described below, as planned by the writer.
5. In the bell instrument applied by Sir C. Bright for receiving Highton's signals by sound; in the system adopted by the Continental Telegraph Union; and in Mr Wheatstone's new self-recording telegraphic instruments.
6. In the signalling of a few words by the writer of this article on board the Agamemnon, approaching the Irish
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1 It seems to the writer most probable that an "electric current" is a real flow of some fluid. But so little do we know of the ultimate nature of electricity, that we cannot tell whether the vitreous or so-called positive, or the resinous or so-called negative excitement is caused by an accumulation of the true fluid. Even the infinitely improbable hypothesis of two fluids flowing in opposite directions to constitute an "electric current," has been accepted by some.
2 Positive, zero, and negative, being reckoned as three degrees.
As for instance, one current, and zero, or positive and negative, with no signal zero. coast, which were read correctly on his marine galvanometer on board the Niagara, approaching Newfoundland.
To Class II. belong—1. Morse's system of electro-magnetically self-recording signals. 2. Bain's system of electro-chemically self-recording signals. 3. Henley's magneto-electric signals. 4. Every other method, whether by batteries, by volta-induction coils, or by magneto-induction machines, for signalling by the Morse alphabet; now much used over the continent of Europe, and in the telegraphs of the East; also in the Atlantic Telegraph during the three weeks of its successful working between Valencia and Newfoundland; also now almost exclusively by the English "Electric and International Telegraph Company."
5. Wheatstone's step by step telegraph, read by eye, which, with modifications introduced by various makers, was used almost exclusively on the continent of Europe until a few years ago. 6. Wheatstone's printing telegraph, and House's American patent mechanism for carrying it into practice. 7. Hughes' American printing telegraph.
VII.—DESCRIPTION OF TELEGRAPHS, DISTINGUISHING THREE DEGREES OF CURRENT.
We shall now proceed to describe very briefly the chief characteristics of these different systems, referring to them by numbers, according to the preceding classification.
Class I.—Variety 1. The transmitting apparatus consists of a galvanic battery, with a hand-key and connections arranged to act as follows:
(1.) The handle of the key, when left to itself, is urged by springs into a vertically downward position, and keeps the line in connection with the earth.
(2.) When turned to one side, it produces at once contact between the negative pole of the battery and the earth, and a contact between the positive pole of the battery and the line.
(3.) When turned to the other side, it produces at once a contact between the positive pole of the battery and the earth, and a contact between the negative pole and the line.
The receiving apparatus consists of a magnetised steel needle, balanced on a horizontal axle or shaft, so as to hang in a vertical position in the interior of a coil of fine wire, and prevented by stops from being deflected to more than a small fixed angle to either side of the vertical. The axle of the needle, prolonged through a division in the coil to the outside, carries a light indicating bar or needle in a conspicuous position in front of a vertical dial-plate, behind which the coil is fixed. This indicating-needle ought to be no more massive than is necessary for rigidity and easy enough visibility. It may with advantage be made of ivory; and the original idea of making it of steel, because it was supposed to be advantageous to have it magnetised in the opposite direction to the inner or efficient needle, is now recognised as a mistake.
The key of the transmitting apparatus, and the whole receiving apparatus, are arranged in a single case, the handle of the former being a short distance below the needle, and in front of a continuation of the dial-plate. This combination, constituting what is called the instrument, is placed in a convenient position to be used by the operator either standing or sitting before the dial-plate. The two ends of the coil are connected permanently, one with the line, and the other with the line connection of the key. Thus, ordinarily, the key, when operated with, sends its currents through the coil into the line; and when left in its middle position, allows any currents which may come from the other end to pass to earth through the coil. Sometimes a short metallic connection is applied by means of a "short circuiting" key, screw-stop, or other arrangement, between the two ends of the coil, when the instrument is being used for transmission,—as, for instance, if the line is badly insulated, and it is desired to spend no power against unnecessary resistance; but most frequently the currents of transmission are all sent through the coil, and thus the operator sees by the resulting motions of the needle on the dial before him, (which should exactly follow the motions of his hand,) that he is performing his manipulations correctly, and with perfect effect.
The "single needle instrument" is adapted to work through one telegraphic wire, in the manner just described.
The "double needle instrument" consists of two single needle instruments, connected separately with two telegraph wires, and put together in one case, so as to show two needles side by side on one large dial-plate, and to present two handles below them, to be worked by the right and left hands of the operator respectively.
The appearance of these instruments, especially of the double needle instrument, is no doubt familiar to many of our readers, being to be seen at almost all the chief railway stations of England and Scotland. The annexed figures will sufficiently explain the interior, construction, and connections of the whole apparatus.
The system first introduced under Cooke and Wheat- stone's patent of 1837 involved the use of five line-wires, and five indicating needles, each with a right and left deflection from its middle position; but the double wire telegraph quickly superseded it, and was for many years employed in all the works of the original "Electric Telegraph Company" of England, now called the "Electric and International Telegraph Company." The double-needle instrument, being always used when two-line wires were available, was worked as a single-needle instrument with one of its needles and keys alone in action, in case of a temporary failure of one of the wires. For many years after their first introduction, these instruments were made with needles so heavy that they could only be worked at a very slow speed, not more than three or four words a minute being attainable on the single-needle instrument, nor than five or six on the double. Although a much higher speed is now attained in consequence of the introduction of lighter needles, the rapidity of action is still limited by their inertia, which (especially by giving rise to vibrations, when the key is put into its middle position so as to allow the current to cease and release the needle from pressing against its stop on either side) necessitates a rate of working to ensure distinctness of signals, which is much lower than the highest that could be easily and accurately performed by a skilful manipulator. The hand-keys are also objectionable, on account of the great space through which they must be moved, and the force required to move them, to produce the signals; and if the needles were as quick as they might readily be made, a good operator would begin to find his speed limited by the muscular effort required to work as fast as his mind could guide him, and as the receiving operator at the other end could read his signals by eye.
2. Steinheil's telegraph of 1837, carried out in actual practice between Munich and Bogenhausen, separated by a distance of 12 English miles, consisted of a transmitting apparatus, a single "main electrode," a receiving instrument, and earth connections precisely as shown above in the general plan, figs. 2 and 3; and its system of signalling was founded on the use of the positive and negative current as distinct elements, with pauses of time to distinguish the consecutive successions of signals representing the individual letters. It was, in fact, the first practical one-wire telegraph on the system used afterwards in England, casually in the old "single needle" of the "Electric Telegraph Company," and regularly in Highton's single-needle instrument as adopted by the "British" company. It is now likely to supersede all other systems of inland telegraph in Europe.
Steinheil's transmitting instrument was an electro-magnetic machine, used to give a positive electromotive impulse to the line by one motion, and a negative impulse by the reverse motion, of a coil of wire in the neighbourhood of a steel magnet; but the other parts of his telegraph were equally adapted for the use of a battery as electromotor, with any manipulating key constructed to give the positive, the zero, and the negative connections at pleasure. The double-spring key indicated above in the general plan (fig. 3), and described more minutely below (Art. 4), would be the best possible for this purpose.
Various forms of receiving instrument were invented by Steinheil, each of which has now come into extensive practical use. The simplest was a single needle, indicating to the eye the two varieties of signal by its right and left motions. The addition of two bells on the two sides allowed the indications to be perceived by ear, and their successions interpreted into letters, words, and sentences without the aid of any other sense. The telegraph was thus literally endowed with the power of speech. In a third instrument two needles were used, one to move under the influence of the positive, and the other of the negative current, each carrying a light tube of ink, by which, when deflected, it marked its signal on a slip of paper, drawn along by clock-work so as to receive the marks of the two needles in two rows of dots; and thus the telegraph was made to write down its tale in enduring symbols, having precisely the same expressive character and power as printed, or as the most distinct of written, letters. In Steinheil's alphabet, letters are essentially represented by—(1), Two single deflections to right and left; (2), Four combinations of two consecutive deflections, right or left; (3), Nine combinations of three consecutive right or left deflections; and (4), Eleven of the sixteen combinations of four consecutive right or left deflections. With no less convenience than justice, we may call by the general designation of Steinheil alphabets, or systems, all in which the same two elementary electric signals are used, according to the same principle of combination. All practical single-wire telegraphs of Class I., as we shall see, are founded on the Steinheil system thus defined.
3. Highton's instrument is adapted to signal on the Steinheil system, through one telegraph wire. It is simply a "single needle," with some modifications of form and dimension, which render it capable of working at a higher speed. Instead of the straight needle of the original instrument, it has a small, light horse-shoe magnet, turning round a horizontal axis in a line through the centre of its bend, and midway between its poles, on a shaft which bears a thin rhombus of ivory for index, attached to it by an acute angle, and hanging down in front of a black dial. The sending apparatus consists of a galvanic battery, and a key presenting two flat levers of ebony or ivory, working up and down on spring-joints when pressed and released by the operator, who generally applies one hand to one of them, and the other to the other. When one of these levers is pressed down, the positive pole of the battery is thrown to the line, and the negative to the earth; and when the other is pressed, the same connections are made with the poles reversed. When neither is touched, the line is kept to earth simply, and both poles of the battery are left insulated. It is found practicable to operate at a considerably higher speed with this instrument than with the original single-needle instrument; so that by means of it, with the alphabet arranged for it by Highton, nearly as much work can be done through one wire as through two by the common double-needle system. It is to be observed, however, that much of this gain in speed is due to the excellence of Highton's alphabet, which appears to be the first electro-telegraphic alphabet constructed on the true principle of representing the letters of most frequent occurrence by the most rapidly executed signals, whether simple or complex, and which is probably somewhat better than the original Steinheil, and undoubtedly a very great improvement on the first English single-needle alphabet.
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1 The original Steinheil alphabet was arranged to imitate, in a necessarily incomplete manner, the forms of printed letters, by the groups of dots in which his telegraph writes them. In the single-needle causal system of the Electric Telegraph Company, the letters are represented by numbers of right and left deflections, corresponding in some arbitrary way with their order in the alphabet. Experience has, however, shown, that the memory neither requires aid, nor is effectively aided, by any such relations, however natural it may have been felt to lean upon them in first attempts to practise to novel art as that of communicating intelligence by words spelled in letters composed from only two distinct elementary signals. After a very short time of learning, it is quite as easy to distinguish with perfect readiness the Highton-Steinheil or the Morse letters, when recorded in Steinheil's dots, or in the Morse dot and dash (to be explained below), or to recollect the manipulation required to execute them, as it is to read Greek, Roman, or German printed characters, or to write the letters of any of these alphabets. The form of instruments to which we have now alluded was patented by the Rev. H. Highton, M.A., and Mr E. Highton, C.E., in 1848, along with various other improvements and inventions in electro-telegraphic apparatus. One part of this patent is so remarkable for the ingenuity and the simplicity of the idea involved, that we quote the following statement regarding it from Mr E. Highton's treatise, which, with the accompanying drawing, will make it sufficiently clear:—"The maximum work capable of being produced by any number of lines was taken advantage of, and thus three wires were made to produce twenty-six primary signals, and so to show instantly any desired letter of the alphabet." Suitable keys were devised for sending currents of electricity over three wires in the twenty-six orders of variation. "Direct-action printing telegraphs were devised, so that a single touch of one out of twenty-six keys caused instantly any desired one out of twenty-six letters or symbols to be printed" at the remote station. The mode in which letters are shown by the combined motions of the three screens is obvious from the drawing. The simplicity of the plan and the ingenuity of the invention are admirable; but the circumstance that it requires three telegraph wires is fatal to its extensive adoption as a practical system.
Another very remarkable telegraph instrument which, as we have been informed, has been introduced in actual practice, although to no great extent, the subject of an earlier patent (1846), invented by the Rev. H. Highton alone, is thus described in his brother's treatise:—"A small slip of gold-leaf, inserted in a glass tube, was made to form part of the electric circuit of the line-wire. A permanent magnet was placed in close proximity thereto. When a current of electricity was passed along the line-wire, the strip of gold-leaf was instantly moved to the right or left, according to the direction of the current." The annexed figure (fig. 7) represents this instrument. The signal system here clearly is of the Steinheil class, as defined above. The alphabet represented on the dial of the instrument is the same as that of the Highton single-needle instrument.
4. A great improvement on the single-needle instrument is to be made by using two needles, each resting against a stop when uninfluenced by the current, and arranged so that one of them shall be moved when the current flows in one direction through the coil, and the other when it flows in the other direction. This was suggested as a particular case of a multiple-needle instrument to distinguish any number of different degrees of current received from one line of telegraph, by the writer of the present article, in a communication to the Royal Society of London of December 1857. The same idea appears to have occurred independently to various inventors, and indeed to have been used in Steinheil's recording telegraphs of 1837. An electro-magnetic receiving instrument on a principle involving it was patented by Messrs Bright in 1855, which has recently been applied, with admirable effect, in Sir Charles Bright's bell relay delivering signals by sound. Wheatstone's automatic recording telegraph marks by double needle on the same principle. There are obviously many different ways of putting it in practice. Thus the two needles may be mounted so as to turn independently on one shaft. They may be magnetised with similar poles in the near ends, and while urged by a fixed steel magnet to place their magnetic axes parallel, they may be held by a stop in positions somewhat inclined to one another. The two needles thus arranged will move, one alone in one direction, under the influence of the positive current, and the other alone in the contrary direction, under the influence... of the negative current. This is the particular plan which the author prefers. Otherwise, the two needles may be magnetised in contrary directions and held by springs or by gravity, so as to rest against a stop, with their magnetic axes parallel; and in this case one will move from the stop, under the influence of one current, and the other will move from the same stop in the same direction, under the influence of the contrary current. By arranging a second stop for each needle to limit its motion to a small angle, the time required to complete the movement for each signal may, as will be readily understood, be made extremely short.
For a sending key adapted to work in the telegraphic systems which have been described, the following plan is much simpler, and allows much easier and consequently more rapid manipulation than any hitherto adopted in practical telegraphic work. Two flat springs, EE', LL', are fixed at their ends, E and L, to a slab of vulcanite, and set so as to press upwards upon a metallic bar, PP', fixed by its ends, P, P', to two blocks of vulcanite, borne by the main slab. Under this bar, and concealed from it in the upper sketch or ground-plan, is another, shown as NN' in section below. This second bar, set in the slab of vulcanite (not shown), allows the springs (which are shown in their natural position, pressing against the upper bar) a little space to move when pressed down. The springs are, by suitable conductors, attached to them at their fixed ends, put in connection with the earth and the line of telegraph respectively. The two bars, PP, NN', are put in connection with the positive and negative poles of the battery respectively. The free ends, E, L, of the springs are coated with vulcanite, so that they may be pressed by finger applied in the positions marked (+), (−), without sensibly deranging the insulation by the body of the operator, or giving him a shock when high battery-power is employed. The action of this key will be readily understood when it is remarked that—
(1) The springs in their natural positions pressing upwards keep the line and earth in connection with one another, and with the positive pole of the battery, through the upper bar, and leave the negative pole of the battery insulated.
(2) When the earth spring, E, is pressed down by a finger applied at (+), the earth connection is thrown on the negative pole of the battery; and the positive pole is left on the telegraph line, which will therefore receive positive electricity.
(3) When the line-spring, L, is pressed by a finger applied at (−), the positive pole of the battery is left in connection with the earth; and the line is thrown into connection with the negative pole of the battery, and will therefore receive negative electricity.
The details of construction are too obvious to require even suggestion here. A key on this plan, with properly platinised contacts, could scarcely go wrong; and it is so free from intricacy that, even if any of the contacts were ever to fail, which could only happen from some non-conducting matter getting by accident between the pieces of platinum which should touch, it could be put right again with the greatest ease. The space allowed for the springs to move may, without producing any liability to false contacts, be reduced to the smallest across which air will insulate. This might be much less than \( \frac{1}{50} \)th of an inch if only fifty cells of Daniell's are used; and if required to insulate even against the enormous power of 5000 cells, need be no more than \( \frac{1}{50} \)th of an inch (according to experiments by the writer of this article on the lengths of spark produced by different degrees of electromotive force absolutely measured), provided always the resistance in the line is sufficient to make the current through it too weak to originate an "electric arc" on breaking metallic contact in the key.
Practically, all things considered, \( \frac{1}{50} \)th of an inch would be quite enough of motion to make sure of correct electrical action in the key; and any space from this to \( \frac{1}{50} \)th of an inch would make the manipulation as easy and rapid as possible.
5. Steinheil's beautiful idea of receiving telegraphic signals by the sound of two bells, struck by the needle or needles, when deflected by two currents (positive and negative) respectively, has been recently put into practice on a very extensive scale, by Sir Charles Bright, with the aid of a simple and effective relay, represented in the annexed figure which he has invented for the purpose, and which proves most successful. This relay, with a local battery supplying the mechanical power required to strike the bells, has been substituted at the principal stations of the British and Irish Magnetic Telegraph Company in England and Scotland, instead of Highton's single needle (which is still retained on their railway circuits, and some of their less important commercial circuits); and the writer is informed, that "for ordinary circuits nothing can work better; that more work can be got from one clerk and one wire by it than by any other receiving instrument;" and that it is gradually being extended to the utmost in the telegraphs of that company. The transmitting instrument used for sending is still Highton's key described above; and it is worked by the staff of operators and clerks trained under Highton's system. The receiving clerk sits between the two bells, and, with only the ear engaged in receiving the signals, writes down his interpretation of their meaning with a degree of ease and accuracy not attainable when one clerk has to watch the needle and dictate his interpretation to another who writes it down, as in receiving by the needle instruments or any other instrument indicating by transient visual signs.
Steinheil's system (positive and negative signals distinguished), with his recording instrument marking by dots in two rows, has been recently introduced in France, and is likely to supersede all other systems of European inland telegraphy. On long lines of telegraph, his ink-marker, when attached to a needle, worked immediately by the current from the line, did not prove effective for want of motive power, but this want is supplied by the use of a relay and local battery; and the marking process is worked in a satisfactory manner either with Steinheil's ink-tubes, or with other kinds of ink-markers, or with Morse's or Bain's plans of marking, to be explained below. The Steinheil self-recording telegraph, with relay, and one or other of these forms of marker, is now in very general use on the continent of Europe, and is worked according to the alphabet of the Telegraph Union; that is to say, the common Morse alphabet (which will be explained below), with positive and negative signals substituted for the dot and the dash respectively. The necessity for a relay to record on the Steinheil system has been superseded by a most ingenious and beautiful invention of Professor Wheatstone's—the ink-maker of his "automatic telegraph," described below—which proves effective for marking dots by as delicate a motion of a needle as any that can be used to produce relay contacts.
This, along with many other excellent contrivances for all parts of the telegraphic process, especially an instrument for perforating slips of paper to be used in an automatic sender, according to the general plan invented by Bain, but carried out in a very novel manner, forms the subject of one of his two recent patents, entitled "Electric Telegraphs," both bearing date June 2, 1858. For full information and details of construction, the reader is referred to the specification, which is amply illustrated by drawings.
The following extracts explain sufficiently the general character and operation of the instruments:
"My invention consists of a new combination of mechanism for the purpose of transmitting through a telegraphic circuit messages previously prepared, and causing them to be recorded or printed at a distant station. Long strips or ribbons of paper are perforated by a machine constructed for the purpose, with apertures grouped to represent the letters of the alphabet and other signs. A strip thus perforated is then placed in a instrument associated with a rheomotor (or source of electric power), which, on being set in motion, moves it along, and causes it to pass over two pins in such manner that when one of them is elevated the current is transmitted to the telegraphic circuit in one direction, and when the other is elevated it is transmitted in the opposite direction; the elevations and depressions of the pins are governed by the apertures and intervening intervals. These currents, following each other indifferently in the two opposite directions, act upon a printing or writing instrument at a distant station, in such manner as to produce corresponding marks on a ribbon of paper moved by appropriate mechanism.
"I will proceed to describe more particularly the several parts of this telegraphic system, observing, however, that each part has its independent originality, and may be associated with other apparatus already known.
"The first improvement consists of an instrument for perforating the slips of paper with the apertures in the order required to form the message. The slip of paper passes through a guiding groove, at the bottom of which an opening is made sufficiently large to admit of the to-and-fro motion of the upper end of a frame containing three punches, the extremities of which are in the same transverse line. Each of these punches is capable of being separately elevated by an appropriate finger-key. By the pressure of either finger-key, besides the elevation of its corresponding punch, in order to perforate the paper, two different results are successively effected: first, the raising of a clip which holds the paper firmly in its place; and, secondly, the advancing motion of the frame containing the three punches, by which the punch which is raised carries the ribbon of paper forward the proper distance. During the reaction of the key, consequent on the removal of the pressure, the clip first fastens the paper, and then the frame falls back to its normal position. The two external keys and punches are employed to make the holes, which grouped together represent letters and other characters, and the middle punch to make holes which mark the intervals between the letters."
"The second improvement consists of an apparatus which may be called the transmitter, the object of which is to receive the slips of paper prepared by the previously described instrument or perforator, and to transmit the currents produced by a voltaic battery or other rheomotor in the order and direction corresponding to holes perforated in the slip; this it effects by mechanism somewhat similar to that by which the perforator performs its functions. An eccentric produces and regulates the occurrence of three distinct movements: 1st, The to-and-fro motion of a small frame, which contains a grooved flange to receive a slip of paper, and to carry it forward by its advancing motion; 2d, the elevation and depression of a spring-clip, which holds the slip of paper firmly during the receding motion, but allows it to move freely during the advancing motion; 3d, the simultaneous elevation of three wires placed parallel to each other, resting at one of their ends on the eccentric, and their free ends entering corresponding holes in the grooved frame; these three wires are not fixed to the axis of the eccentric, but each of them rests against it by the upward action of a spring, so that when a light pressure is exerted on the free end of either of them, it is capable of being separately depressed. When the slip of paper is not inserted, and the eccentric is in action, a pin attached to each of the external wires passes, during each advancing and receding motion of the frame, from contact with one spring into contact with another spring; and an arrangement is adopted, by means of insulations and contacts properly applied, by which, while one of the wires is depressed and the other remains elevated, the current passes from the voltaic battery to the telegraphic circuit in one direction, and passes in the other direction when the wire before elevated is depressed, and vice versed; but while both wires are simultaneously elevated or depressed, the passage of the current is interrupted. When the prepared slip of paper is placed in the groove and moved onwards, whenever the end of one of the wires enters an aperture in its corresponding row, the current passes in one direction; and when the end of the other wire enters an aperture of the other row, it passes in the other direction. By this means the currents are caused to succeed each other automatically in the proper order and direction to give the requisite variety of signals. The middle wire only acts as a guide to the paper during the cessation of the currents. The wheel which drives the eccentric may be turned by hand, or by the application of any motive power."
"Instead of a voltaic battery, a magneto-electric or an electromagnetic machine may be employed as the source of electric power. In this case, the transmitter and the magneto-electric or electromagnetic machine form a single apparatus moved by the same power, and they are so adapted to each other, that the shocks or currents are produced at the moments the pins of the transmitter enter the apertures of the perforated paper."
"The transmitters just mentioned require only a single wire of communication, and currents in both directions are available for printing the signals; but in some cases it may be advantageous to employ two telegraphic wires, and to use the inversions of current to bring back the pens or markers without the aid of reacting springs. In this case the only modification of the apparatus required is in the disposition of the insulations and contacts necessary to transmit, in their proper order, the currents from the rheomotor into the two wires."
"The third improvement is in the recording or printing apparatus, which prints or impresses legible marks on a strip of paper, corresponding in their arrangement with the apertures in the perforated paper. The pens or styles are depressed and elevated by their connection with the moving parts of the electro-magnets; they are entirely independent of each other in their action, and are so arranged, that when the current passes through the coils of the electro-magnets in one direction, one of the pens is depressed, and when it passes in the contrary direction, the other pen is depressed; when the currents cease, light springs restore the pens to their usual elevated positions. The mode of supplying the pens with ink is as follows:—A reservoir, about an eighth of an inch deep, and of any convenient length and breadth, is made in a piece of metal, the interior of which may be gilt, in order to avoid the corrosive action of the ink placed in it; at the bottom of this reservoir are two holes, sufficiently small to prevent, by capillary attraction, the ink from flowing through them; the ends of the pens are placed immediately above these small apertures, which they enter, when the electro-magnets act upon them, carrying with them a sufficient charge of ink to make a legible mark on the strip of paper passing beneath them. The motion of the paper ribbon is produced and regulated by apparatus similar to those employed in other registered mailing telegraphs."
"The fourth improvement is an arrangement which I call a translator. Its object is to translate the telegraphic signs, consisting of successions of points or marks, adopted in this system, into the ordinary alphabetic characters. In the system I have adopted, limiting the number of points in succession to four, 30 distinct characters are represented. The instrument presents externally nine finger-stops, eight of which are arranged in two parallel rows, four in each, and the remaining one is placed separately. The principal part of the mechanism within is a wheel, on the circumference of which 30 types are placed at equal distances, representing the letters of the alphabet and other characters; other mechanism is so disposed and connected thereto, that when the keys of the upper row are respectively depressed, the wheel is caused to advance 1, 2, 4, or 8 steps or letters; and when those of the lower row are, in like manner, depressed, the wheel advances respectively 2, 4, 8, or 16 steps. By this disposition, when the stops are touched successively in the order in which the points are printed on the paper, touching the first stop for one point, the first and second for two points, &c., and selecting the stops of the upper or lower row, according as the point is in the upper or lower row of the printed ribbon, the type-wheel will be brought into the proper position for printing the letter corresponding to the succession of points over a ribbon of paper. The ninth stop, when it is pressed down, acts to impress the type on the paper, to cause the advance of the paper, in order to bring a fresh place beneath the type-wheel, and subsequently to restore the type-wheel to its initial position." The instrument described in the preceding extracts, or "Wheatstone's automatic telegraph," as it is called, is capable of recording 500 letters per minute with certainty, through short aerial lines, which is probably the highest speed yet attained on any system.
6. A few words, and one important message, "Send alternate currents," were transmitted by the writer on board the Agamemnon, approaching the Irish coast, and were correctly read on his "marine galvanometer," on board the Niagara, approaching Newfoundland. The alphabet employed was one on Steinheil's system (agreeing with Hilton's so far as having the combinations in order of brevity arranged to correspond with the letters in order of frequency), which was drawn up merely for temporary use. The mode of manipulation in the transmission of these signals, by means of a common three-position reversing-key, was peculiar, involving the counting of time by the beats of a watch, to produce compensations for inductive embarrassment on the principles indicated by the mathematical theory, and, without the aid of a proper instrument, would be too troublesome for general use. With a key of very simple construction for enabling the operator to apply definite electromotive forces during accurately measured intervals of time, which the writer has recently constructed, this system will probably be found more advantageous, in point of speed and certainty, than any hitherto practised through long submarine lines.
VIII.—TELEGRAPHS USING ONLY TWO DEGREES OF CURRENT.
1. In Morse's telegraph, which is the simplest conceivable, a current is, by the application of a battery, made to flow through the line for a longer or shorter time, and longer or shorter intervals of no current are allowed to elapse between such successive battery applications. The effects are recorded at the receiving station on a long ribbon of paper, made to run uniformly by wheel-work by a metal point attached to a lever, bearing the armature of an electro-magnet. The coil of this electro-magnet is put in circuit between the line of telegraph and the earth, when the signal currents are strong enough to produce the required effect by their own power. This, however, is not generally the case unless in very short or very well insulated lines, and almost universally now a local, or "relay" battery, according to one of Wheatstone's inventions, specified in 1837, is employed at the receiving station to do the forcible mechanical work of recording, under direction of the signal currents from the distant station, which make and break contact for it, and do no other work.
When there is no current through the line, the recording electro-magnet is inactive, and the lever is held by a spring, so as to keep the point off the paper. When a current is received, the electro-magnet becomes excited, either directly or by the relay battery, attracts its armature, and causes the point to be pressed on the paper, so as to indent or emboss a line upon it, of which the length is equal to the space run by the paper during the time the current flows. The result, a series of marks, some very short, called dots, and some longer, called dashes or lines, separated from one another by blank spaces of various lengths, is seen on the paper as it runs from the machine, and constitutes a record of the durations of current by the marks, and no current by the blanks. Signals of this character may, as we shall see, be combined in a variety of ways, to constitute the letters and signs used in the communication of intelligence. The alphabet introduced by Morse is founded on the combination of dots and dashes into groups, to represent the individual letters and signs; the dots and dashes of each group being separated from one another by the shortest blank interval, and the groups separated from one another by decidedly longer blanks. The successions of letters constituting words are separated by still longer intervals when clearness requires such a distinction.
The Morse alphabet is, in fact, composed from two distinct elementary signals, according to precisely the same numerical combinations as the old single needle, or Hilton's perfected alphabet. Accordingly operators familiar with the Morse alphabet sometimes work a single needle instrument, using one deflection (to the right, for instance) instead of the dot, and the contrary deflection (left) for the dash. This mode of signalling, when both sending and receiving instruments are adapted to distinguish positive and negative currents, is of course more rapid than the Morse system, as it saves the time required for the prolongation of the deflections to constitute dashes. It has very recently been adopted in connection with recording apparatus for receiving, by the French government, and the Telegraphic Union.
The transmitting apparatus used by Morse, and by nearly all who have adopted his system of signals, consists of a galvanic battery, and a key for making and breaking contact with the line. The form of key most generally employed for this purpose has been taken from that in general use in America, "invented" and first made by a philosophical instrument-maker of New York. It is much the reverse of an improvement on "the rude instrument," consisting of "a slip of sheet-copper, with one end fastened to the table, while the other, being loose, yielded as a spring, and was moved with the fingers to break and close the circuit," by which Morse first worked his telegraph, and which, with the substitution of brass, as more elastic, in place of the copper slip, and with the addition of a stop to limit the upward motion of the spring, is the best and simplest possible apparatus for producing the required effects, and is immensely superior to the massive lever "Morse key" constructed by even some of the best and most scientific European telegraph instrument-makers of the present day. The upper stop is generally metallic also, and is connected with the earth, so that when the key is up, the line is thrown into connection with the earth. It is true that the so-called "Bavarian Morse key," having a simple spring and no lever, sometimes gives false contacts when not pressed in exactly the right direction by the operator, and has this defect only imperfectly remedied by a certain screw adjustment; but a slight alteration in the relative position of some of the parts does away with all necessity for adjusting screws, and gives an instrument which, while simpler and cheaper than any other, can never go wrong, and presents the greatest possible facility for rapid working. A single spring-key, on precisely the same plan as either spring alone of the double spring-key, sketched above (VII. 4.), has these qualities.
2. In Bain's electro-chemical system, signals of precisely the same character as in Morse's are adopted (similar, in some cases identical, combinations of the dot and dash being used to represent letters of the alphabet, and other more or less complex elements of intelligence). They are recorded by the current itself on paper moistened with prussiate of potash, and other chemicals in solution, carried round on a brass tablet by wheel-work, and gently pressed by a metal style of steel or copper, conducting the electric
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1 For short air-lines this is not necessary, but is quite essential for rapid working through submarine telegraphs of considerable extent, when the charge accumulated in the line does not escape between signal and signal with sufficient rapidity through the receiving end alone. Telegraph, Electric.
Telegraphs current between the telegraph line and the earth; the style being connected with the line and the tablet with the earth if the signal currents are positive, or the style with the earth and the tablet with the line if, as possibly ought always to be, the signal currents are made negative for the sake of preserving the line from corrosion by moisture about the insulators. The following description of Bain's receiving instrument, and the perspective drawing which accompanies it, are extracted from Jones' Historical Sketch of the Electric Telegraph (New York, 1852):
"In the figure (fig. 10), the clock-work which moves the tablet is seen on the right. Its motion is regulated by a fly-wheel above, the vanes of which can be inclined so as to present greater or less resistance to the air. A lever or brake bears upon the axle of the fly-wheel, by moving which lever the clock-work may be stopped, or allowed to go on. The circular disc, or tablet of brass, carried by the clock-work, is seen on the left of the figure, inclined towards the observer. In the centre of this disc, occupying the shaded portion, a spiral groove is cut, in which the guide to the pen travels. This guide is seen attached at right angles to the penholder, which extends over the disc. The wire is prevented by a little clamp, descending so as to touch the tablet. This wire, of course, traces a spiral line of dots upon the outer ring of the disc's surface, exactly corresponding, in the distance of its lines, to the spiral groove within, which serves as a guide. By this beautiful contrivance, the writing is disposed in a close spiral line of dots, to represent letters, occupying but very little space.
The outer part of the surface of the disc, upon which the letters are represented in the figure, is covered with a ring of moistened and chemically prepared paper. This may be renewed or removed at pleasure. The penholder is connected with the positive wire of the telegraph, and the tablet with the negative. The circuit of conductors is completed by the moistened paper which intervenes, and which the current accordingly traverses. This paper is moistened with a solution of the yellow prussiate of potash, acidulated with nitric or sulphuric acid. The pen-wire consists of iron. When the current passes, this pen-wire is attacked by the solution, and the portion of iron dissolved unites with the prussiate of potash to form the colour known as Prussian blue, which permanently stains or dyes the paper."
The indication of the current here takes place without motion. The pen itself never stirs [except in its slow radial motion outwards]; it bears silently on the paper; and as the eye observes the point of contact, now a blank space, and now a deep blue line, appears upon the retreating surface. This is the record of the intermittent current sent over the wire from a distance."
This admirable method of recording electric signals is now used very extensively both in America and in the Old World, although in general applied not directly to the currents received from the line (which would not in most cases be strong enough to produce visible marks), but to currents generated by a local or "relay" battery at the receiving station, according to contacts made and broken by electro-magnetic action of the primary signal currents, as in the relay arrangement introduced to work the Morse Telegraphs recording system, as described above.
The only other modification which has been applied to Bain's recording system, is the employment of a long ribbon of paper, running by wheel-work like that of Morse, which is found more convenient than the circular tablet first employed by Bain.
Another excellent invention of Bain's—a plan for transmitting apparatus—is included in the same patent (1846) as that in which he first specifies his electro-chemical recorder. It is described and commented on in the following terms by Highton:
"A plan for transmitting a message more rapidly than can be done by hand, consisted in cutting out slits of different lengths in a long slip of paper at the transmitting station, and allowing this perforated strip to pass uniformly over a metal cylinder with a pin or spring pressing on the top of the paper. Whenever, therefore, a hole in the paper passed under the pin, the pin came into metallic contact with the cylinder underneath, and allowed a current of electricity to pass through the line-wire. All the holes in the strip, and thus all the slits, were consequently proportionably represented at the distant station by chemical marks of corresponding lengths on the prepared paper at that station. This form of telegraph is the quickest at present invented. It does not, however, seem suited to ordinary communications, but only to the transmission of very long documents on extraordinary occasions.
"If one person only is employed to punch holes in the paper, it is evident that, instead of making a hole in the paper, a current of electricity might as readily be sent, and a chemical mark made at the distant station; and thus the message might actually be sent in the same time as that required for cutting the paper. But this remark applies only to the case where there is but one attendant for a wire. If a number of men be employed at each station, then, by dividing the message into parts, and each man punching out his part, the whole paper can be perforated in less time than one man could send the message. On uniting this perforated paper, and applying it to a machine, and on turning the cylinder round, corresponding chemical marks may be made at a distant station with very great rapidity."
Mr Highton proceeds to remark—"The commercial question is, therefore, where ordinary communications are alone required, one of large working expenses versus a rather larger outlay of capital in the first instance." With this we cannot agree. It appears clear that the working expenses in carrying out Bain's plans, if the mechanical and electrical success were complete, must be less than would be required to do the same amount of work by hand through several wires, since only the same number of men will be required (the punching instrument being, it is to be presumed, workable at the same rate as a hand-transmitting key), and the expenses of maintaining the extra wires and battery power would be saved. The fact that this plan has not come into universal use, on all lines where there is more work to be done than can be got through one wire by one hand, does not find its correct explanation in Mr Highton's remarks. It seems more probable that some electrical or mechanical imperfection, which may be remediable, has hitherto operated against the complete success of this admirable invention; and we are disposed to conclude that perseverance in attempts to improve its details, would be rewarded by the achievement of a vast extension of the work done through the electric telegraph by land.
3. The "Magnetic Telegraph," under Henley and Foster's patent of 1848, consists of a double or single magneto-electric machine, sending through two line wires, or only one, to a double-needle or single-needle receiving apparatus, which consists of electro-magnets, with steel needles movable through small angles across the lines of force between their poles. There is no commutator and no breaking of the circuit in the sending machine; but a single motion of a key, when pressed down by the operator, produces an electro-motive impulse, which sends a current through the line; and the return motion of the key, rising by a spring, produces subsequently a reverse impulse and a re- Telegraph, Electric.
Under influence of the first, or direct current, using only as we may call it, the receiving-needle moves from a stop, on which it rests during cessations of action, and strikes another stop placed to limit its motion. On this second stop it rests until the reverse current brings it smartly back to its normal position. The resting of the needle firmly on either stop is secured by the magnetic force exerted between itself and the soft iron of the electro-magnet.
In the double-needle system of the magnetic telegraph, a single motion and return of either needle constitutes a simple signal; and the alphabet is composed out of two simple signals, as Steinheil's is from positive and negative. In the single-needle magnetic system, the operator works precisely as with a Morse key, and he thus produces short and long deflections, since the needle rests deflected against its limiting stop until the reverse current brings it back; and the alphabet is composed, like the Morse, out of two simple signals, the short or dot, and the long or dash.
These instruments, after being very extensively and successfully used for many years, have been gradually superseded in England by Highton's instruments of the "British" Company, which, with the instruments of the "Magnetic" Company, became the property of the amalgamated "British and Irish Magnetic Telegraph Company." Henley's magnetic instruments are still used in the Irish railway telegraphs of the company. At many of the more important stations Sir C. Bright has introduced his bell relay in connection with them; the double-needle instrument being made to direct the power of a local battery to strike one bell when a current comes through one of the line wires, and another bell when a current comes through the other wire; and the single-needle instrument being similarly arranged to produce on a single bell a mere blow giving a clear sound, or a blow and sustained pressure producing a muffled sound, according as the short signal (dot) or the long signal (dash) is sent.
4. The Morse alphabet, with some modifications, recorded either exactly in Morse's manner, or by Bain's method applied to a ribbon of paper, with marking power, mechanical or chemical, supplied by a local battery, for which contact is made by a "relay" under influence of the signal current, is at the present moment probably more used than any other telegraphic system. It has been carried out in a remarkably perfect manner by the Electric Telegraph Company, with the aid of Mr Cromwell F. Varley's form of relay (patent No. 1318, 1855), a particular and we believe a very excellent form of the class of "polar relays," to which also belong Mr E. W. Siemens' patent, No. 13062, 1850, and Mr Whitehouse's patent, No. 2617, 1855. The general action of polar relays will be perfectly understood by supposing the moving needle, and one or other or both of the two stops in Mr Henley's receiving-instrument, described in the preceding article, to be provided with electrical contacts; so that two conductors, one connected with the needle and the other with one of the stops, shall be put in communication with one another when the needle is thrown over to rest on this stop. A specialty of much importance, involved in Mr Varley's and in Mr W. Siemens' working instruments, was, we believe, first introduced by Mr Siemens in 1850, and that is the use of a moveable soft iron bar, kept magnetic by the influence of a powerful steel magnet, instead of a moveable magnetised steel needle as in Mr Henley's receiving instrument, or a small moveable steel horse-shoe magnet, as in the form of relay which Mr Whitehouse adopted for actual use. We regret that our space does not permit us to describe particularly these several forms of relay. We believe, however, that except when signals are to be read off by sound, the use of a mechanical relay for any other purpose than that of retransmitting signals from point to point by relay batteries along a land line of telegraph exceeding 500 or 600 miles in length (which is advantageous solely in consequence of the necessary imperfection in the insulation of the line) will be discontinued, since it seems certain that mechanical power enough to make the contacts required to work a Morse instrument, or even the much lighter contacts which suffice for marking signals by Bain's recorder, must, when properly applied, be adequate either to make pencil, ink, or other perfectly visible marks, on the Morse long and short principle, or to cause type impressions to be printed, on a ribbon of paper, either without drawing on any local store of energy at all, or without drawing on any other than weights or spring required in any case to drive the mechanism carrying the paper along. Mr Hughes has thus managed his printing instrument described below—a very remarkable achievement of electro-magnetic mechanics; and Professor Wheatstone has superseded all other power than that of the signal current itself, to make ink marks (mere dots) on the Steinheil system. To ink a pen so that it may mark a dash on the moving paper as long as it is held on by the electro-magnetic force of the feeblest signal-current that it is in other respects advisable to use, is the invention wanting to supersede relays in recording apparatus for the Morse system.
No better Morse telegraphic printing through any line, long or short, can be shown than the messages received at Valencia from Newfoundland, a specimen of which is represented in the annexed fac-simile on a scale of one-fourth lineal dimensions.
These messages were recorded in the following manner: The receiving clerk watched the image of a lamp reflected upon a horizontal paper scale, from a mirror galvanometer in circuit between the cable and the earth. Every time he saw the image begin to move towards the right, he pressed a Morse key placed beside him, and every time he saw it begin to come back towards the left, he lifted his hand and released the key. This action made and broke the circuit for a local battery and Bain's recorder, and thus produced marks and blanks consecutively on the ribbon of paper, of lengths proportional to the times during which the spot of light was moving to the right and to the left respectively. The receiving clerk, in fact, acted the part of relay, with what perfection the Valencia telegrams show, as the
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1 The Morse alphabet, as generally used through Europe, bears modifications which have been made chiefly by German telegraphists. It is on the whole better adapted to the German than the English language; and English telegraphers would do well to make several changes on important letters, which could readily be done without confusion. This has been done by the Atlantic operators in the case of the letters M and O, which have been interchanged with much advantage in consequence of the greater frequency of the letter O in the English language. Thus the Atlantic Morse alphabet is as follows:
| A | B | C | D | E | F | G | H | I | J | K | L | M | |---|---|---|---|---|---|---|---|---|---|---|---|---| | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
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This message was received at Valencia from Newfoundland, a specimen of which is represented in the annexed fac-simile on a scale of one-fourth lineal dimensions. Telegraph reader may judge from the specimen of them we present. This system of receiving and recording messages by human relay has great advantages over every other method hitherto tried or proposed for working through long submarine lines. In the first place, the motions directly produced by the signal currents are not, as when a mechanical relay records them, limited by stops. They may therefore be observed through a wide range on either side of zero, and the signals may be clearly disentangled from influences of inductive embarrassment and of earth currents, which would lay the mechanical relay over to one side or the other, and either prevent it from turning and giving any indication at all of the signals intended, or alter the proportions of blanks and marks so as to render it impossible to decipher the result. The human relay, employed in the manner which has been described, to record the motions of a spot of light on a scale, is much more sensitive and more reliable than any mechanical relay can be in the circumstances. A degree of current which cannot turn the most delicate of inanimate relays gives an ample motion to the spot of light. Even when the common relay turns, its contact often fails, or is uncertain, unless it is driven by superabundant power—more than it would be advisable ever to use through an ocean telegraph. The human relay has no corresponding liability to failure. It dispenses with the local battery and chemicals required for working Morse or Bain recorders in the ordinary way; and the simple pressure of the hand, direct on the lever of a Morse instrument, or on a proper appliance for carrying a pencil or other convenient style, allowing it when pressed to bear properly on a ribbon of paper running through regulated wheel-work, gives a most accurate and sure record of Morse signalling through a submarine line at any rate up to ten or twelve words a minute. If, however, the inductive embarrassment is so slight as to allow higher speeds than this to be regularly used, it is probable that the eye, mind, and hand of the human relay might not readily act in combination with the requisite rapidity, and that a common mechanical relay would be necessary or preferable.
The mirror galvanometer, planned by the writer of this article for receiving signals through the Atlantic cable (and available, with advantage in point of speed and the smallness of battery power which it requires, for every submarine telegraph in which, through inductive embarrassment, the ordinary relay method becomes limited to any speed less than ten or twelve words a minute), consists of a very light mirror, with a small bar magnet of file steel cemented to its back, supported, within a helix of insulated wire, by silk fibre allowing it freedom to turn about an axis in its own plane and perpendicular to the magnet attached to it. The apparatus is complete with a lamp and scale attached to a frame bearing also the galvanometer; and a lens bounding one side of the chamber in which the mirror is supported, of such a focal length that rays from any point of the flame shall, after entering through the lens, being reflected by the mirror, and repassing through the lens outwards, be brought to a focus on the scale. In instruments of this kind, designed for land-use, the mirror is generally hung by a single silk fibre, about 4th of an inch long, in the hollowed end of a plug of metal fitting half-way into the cylindrical hollow of the coil, of which the diameter is rather less than half-an-inch. The diameter of the mirror is about 3ths of an inch, and the length of the magnet the same; the weight of mirror and magnet together being from a grain to a grain and a half. Such an instrument, with 500 yards of No. 40 copper wire (weighing '5 grain per foot) in its coil, and with only the earth's magnetic force to direct the needle to its position of equilibrium, will at Glasgow give a deflection moving the spot of light over about 200 divisions of \( \frac{1}{10} \) each, on a scale 24 i from the mirror, when under the influence of an electromotive force equal to \( \frac{1}{10} \) of that of a single cell of Daniell's maintained between the two ends of the coil.
The conductor of the Atlantic cable, which weighed from 110 to 120 grains per foot, was about 220 times as massive as that of the galvanometer coil; and therefore, if of equally good copper, 2400 statute miles of it would have resisted 38 times as much as the 500 yards of the galvanometer. Hence, \( \frac{38}{3} \) of the electromotive force of a single cell would have given 200 divisions of deflection through the whole cable, if perfectly insulated and of good copper. But two or three divisions of deflection are quite sufficient for reading signals from, and therefore one cell of Daniell's would have given more than ample signal-currents through the actual copper of the Atlantic cable, if ordinarily well insulated. The quickness of the galvanometer indications under the directive force we are now supposing—that of the horizontal component of terrestrial magnetism at Glasgow—is nearly sufficient for signalling at the rate of 40 dots per minute\(^2\) (which would give about 2\(\frac{1}{2}\) words per minute); as may be judged from the circumstance, that the natural rate of vibration of the needle and mirror, when deflected and left to oscillate under the terrestrial influence alone, was about 84 vibrations (that is, 42 motions in one direction, and 42 returns). In this condition of the galvanometer, however, the ordinary earth-currents through the cable (when connected with plates of the same metal, sunk in the earth or sea on the two sides of the Atlantic), would far exceed the signal-current, and might often be as much as 20 or 30 cells would produce. There would be no difficulty in compensating their effect by steel magnets properly placed beside the galvanometer, in directions perpendicular to the plane of the mirror; or in directly balancing them with an opposing electromotive force, by means of an instrument for dividing the electromotive force of a battery into any desired number of parts, which the author constructed and applied for the purpose at Valencia. Sometimes, however, in certain terrestrial and atmospheric conditions (especially when aurora borealis is seen), the changes in the earth-currents are so rapid, that they would seem like signals, and render the reading of a message for the time difficult or impossible. By rendering the galvanometer less sensitive, which is best done by introducing steel magnets to add to the earth's directing influence, and using a proportionately more powerful sending battery, this disturbing influence is diminished, and may be rendered practically harmless, or as nearly as possible so. It is convenient in other respects also to have the needle more powerfully directed than by the earth alone; and the action will probably be found in all respects satisfactory, if about nine times the earth's horizontal force at Glasgow is applied to direct the needle (as is easily done by means of a single bar, or two or three bars, of hardened and magnetized steel, a few inches long). The oscillations of the needle will be then three times more rapid (or about 252 per minute), and a battery of 5 cells will be amply sufficient for signalling. If from 10 to 20 cells be used, there will be superabundant power for Morse signalling at the highest attainable rate, with the proper compensations introduced for inductive embarrassment which the mathematical theory has
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1 That is to say, any inanimate electro-magnetic or galvanometric relay. 2 If, for instance, the ordinary relay cannot give more than six words a minute, messages may be perfectly recorded by a mirror galvanometer at the rate of ten words a minute. When there is still more inductive embarrassment, limiting the mechanical relay to four words or less per minute, a double speed may with ease be obtained by the new method. 3 The rate from Newfoundland to Valencia was raised from 20 dots per minute, for which the sending mechanism was prepared, up to from 40 to 42, according to instructions telegraphed from Valencia, when the experience of the mirror galvanometer as a receiving instrument was had. pointed out. If, as is to be hoped will soon be the case, the Red Sea cable is brought into working order, it is probable that 10 words a minute or upwards will be obtained as a regular rate of Morse signaling through one of its sections of from 500 to 700 nautical miles, by using for sending a battery of 10 Daniell's, with a key constructed to produce the theoretical compensations, and, for receiving, a mirror galvanometer, adjusted with a still much higher directive force of steel magnets, recording by "human relay" on a riband of paper to be marked by hand, without local battery, either with a Morse style or pencil (or with Siemens' ink-marking apparatus, constructed on the whole in accordance with a principle brought into use by John in Vienna, and Digney frères in Paris, which has been provided already for the Red Sea Company to be worked by relay and local battery).
The "marine galvanometer" (referred to above, VII.6.), constructed by the writer for use on board the Agamemnon and Niagara, differs from the land mirror galvanometer only in the use of still higher directive force on the needle, and in the mode of suspension of the mirror and needle, which was, by means of a fine platinum wire, or, as has since been found better, a stout bundle of 20 or 30 silk fibres, firmly stretched between two fixed points of support. This instrument, as now constructed with some improvements, is represented in the accompanying drawings. The first shows the back of the mirror with attached needle, (a piece of thin, flat file, ground smooth,) the filament bearing it, the mountings for holding the two ends of the filament, and the bobbin of the front half of the galvanometer coil, which bears these mountings.
The second drawing shows a perspective view of the instrument complete, with stand and lamp, taken from a photograph. The galvanometer itself is protected by a strong plate-glass shade; in the front side of which (not seen) a slit, about 1½ long by ½ broad, is cut to allow the light from the lamp to enter, and to be reflected back from the mirror to the scale without loss by passing through the plate-glass. A large compound magnet of sheet-steel, bent and tempered glass hard, is seen round the galvanometer, and N marks one set of its poles; the other set, of contrary name, is diametrically opposite. By an adjusting screw, A, this magnet can be turned through a considerable angle about a vertical axis, to bring the spot of light to zero, or to any desired point of the scale. On the back of the back half of the galvanometer bobbin are seen rings and screws, forming a system of connections by which four parts of its coil may be used either singly, or connected in series, or in series of double arcs, or entirely in multiple arc. A similar set of connections, not seen in the view represented, are attached on the front, for similar arrangements of the front half of the coil. A set of connections G, on the side of the stand, allow the front and the back halves of the coil to be used either alone, or the two in series, or the two in double arc; and at any time one of these arrangements to be changed for another in a moment; also, to reverse the extreme galvanometer terminals in their connection with binding screws (not seen in the view) for attaching the outer electrodes. Some of the outer connections of a testing apparatus, to be used along with the galvanometer, are seen on a box attached to the frame between the galvanometer and the lamp. This apparatus contains 18 standard resistance coils of German silver, of resistances expressed in terms of 100,000,000 British absolute units by the numbers and fractions, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1, ½, ¼, ⅛, ⅜, ⅝, ⅞: also four conductors of widely different resistances, each accurately bisected (electrically), to be used any one, or in combination, one arm of one with one arm of another, to constitute part arc of a Wheatstone's balance, of which the remainder would be made up of conductor to be tested, and standards. On the remote side of the box (not seen) are connections for applying these bisected conductors in the most convenient possible manner. On the top of the box is a double spring key (not shown) for applying battery electrodes, in either direction, to proper terminals for the Wheatstone's balance when formed; and D represents another kind of double spring key for reversing instantaneously the connections between the terminals of the galvanometer coil and their proper terminals in the "balance." A set of screws on insulated studs
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1 Chosen because it changes less in its resistance, with changes of temperature, than any other metal yet known and available of connection is the same as that originally reduced to practice by Mr Cromwell F. Varley, and makes up the required resistance by the addition of resistances. The second, and the combination of the two plans is entirely novel, and, by allowing conducting powers to be added, gives the same sensibility at the low end of the scale of resistances, that Mr Varley's does at the high end. It is essential that the graduation by 2 and the powers of 2 be followed, in the resistances, when the same set of coils is to be used in the two ways. If they were merely to be used in series, the numbers 1, 2, 3, 5, 10, 12, 13, 15, &c., preferred by Mr Varley, would be somewhat more convenient. Beyond the testing apparatus is seen the top of the lamp-glass, the scale, and the slit behind which the flame of the lamp is placed. A common flat-wicked paraffine lamp is used, with the edge of its flame towards the galvanometer. In performing accurate measurements, the slit in front of the flame is made very fine, by a screw acting on two plates of metal, so as to give a fine line of light to read from on the scale. In using the instrument for receiving telegraphic signals, the slit is made so wide as to allow the full image of the flame to fall on the scale, which will cover two or three of the \( \frac{1}{2} \) divisions.
In the marine galvanometer of this kind hitherto made, the adjusting magnets are so highly magnetised as to give about 200 times the Glasgow terrestrial horizontal directive power. The rapidity of the natural oscillations of the needle is so great as to show merely a spread out hand of light, on the scale, when a current is suddenly made, or broken through the galvanometer coil; but dynamical principles show that it must be about \( \sqrt{200} \) (or 14\( \frac{1}{2} \)) times what has been mentioned above as the natural rate for a similar needle under terrestrial influence at Glasgow alone; and must therefore be about 20 vibrations per second. A single cell applied to the galvanometer coil, arranged in series, gives a deflection of about 75 divisions, on a scale 18\( \frac{1}{2} \) i from the mirror. Care having been taken to balance the needle and mirror, so as to have the centre of gravity precisely in the line of the supporting filament, the indications of the instrument remain steady and undisturbed during the roughest usage it can be exposed to on board ship. The greatest amount of tremulous motion, in the table or support on which it is placed, does not cause vibrations in the spot of light, and the whole may be inclined to an angle of 45° in any direction, without sensibly disturbing the position of the spot of light on the scale.
By diminishing somewhat the magnetism of the adjusting magnets, the instrument may be brought to any requisite degree of sensibility suitable for receiving ordinary telegraphic signals, in the manner explained above, for which it is perfectly adapted; but for the highest degree of sensibility which has been stated, its multiple filament would be unsuitable.
The most complete possible mode of recording telegraphic signals would be to show a curve representing precisely the varying strength of the current received at every moment. An instrument executing this plan has been constructed by the writer, and found to succeed in circumstances essentially more trying to its capabilities than those of actual work through a long submarine line. In this instrument the record consists of minute perforations in a broad ribbon of paper, made by a very rapid succession of sparks from a Ruhmkorff's induction coil, worked by a local battery at the receiving-station. A vertical piece of platinum wire attached to a light horizontal glass index, borne by a finely but firmly suspended magnetic needle, conducts the perforating current from a vessel of water, into which its lower end dips, to the ribbon of paper, which is carried near its upper end in a direction perpendicular to its line of motion. This instrument will disentangle signals from inductive and other embarrassments, in cases in which even the method by mirror galvanometer and human relay fails. But it requires more power to work it, at Telegrapha using only Two Degrees of Current.
5. The first "step by step" telegraph was invented by Wheatstone in 1839, and patented by him in conjunction with Cooke, Jan. 21, 1840. Two kinds of sending instruments for working this telegraph were included in the specification; one consisting of a contact-wheel of peculiar construction, to make and break contact for a galvanic battery; the other a magneto-electric machine, with no commutator, and a wheel and pinion to carry round the coils. The wheel in each instrument was marked with the letters of the alphabet. In the galvanic instrument, contact was made, or was made and broken, every time the wheel was moved, so as to carry one letter after another to a position opposite to a fixed pointer. In the corresponding motion of the wheel of the magnetic machine, the pinion makes a half-turn, carrying the coils from one position of maximum magnetisation of their soft iron cores to the opposite. The mode of operating with either instrument was simply to turn this alphabet-wheel by hand till the particular letter to be signalled was brought opposite to a fixed pointer. The receiving instrument was so constructed and arranged as to show at the same time the same letter, by carrying it round on an alphabet-wheel, moved by the currents, and leaving it opposite to an aperture in a case inclosing the apparatus.
The annexed figure, taken from Highton's work, shows Telegraphs having, instead of a pendulum to regulate its escapement; using only a piece of iron, moved to and fro alternately by the attraction of an electro-magnet excited by the current from the telegraph line, and by the force of a spring bringing it back when the current ceases; or (2), A similar apparatus with no driving weight or main-spring, but having its motion produced as well as regulated by the force of the currents acting through the electro-magnet, and giving the reciprocating motion to the piece of soft iron.
Telegraphs of this kind, with the magneto-electric senders, were first brought into use on the Great Western Railway, where they were worked from 1841 to 1845. In 1845 Mr Wheatstone established them on the Paris and Versailles Railway, where they remained in constant use until a few years ago.
Various step-by-step telegraphs, all on the same principle, with modifications introduced by different makers, were almost exclusively employed on the continent of Europe until within the last few years, when Morse signals, recorded either by Morse's indenting style or Bain's electro-chemical method, or improvements on Steinheil's original plan of marking by ink, applied either to his own system, of positive negative and zero currents distinguished, or to the Morse system, have come to be substituted for them, except for railway purposes, for which they are still retained.
The details of this most pleasing and popular of telegraphic systems have been recently improved with admirable skill and ingenuity by its inventor. In his original instruments (to use his own words), "much remained to be done to render them capable of extensive practical application. Increased speed, greater simplicity, and portability of form, and, above all, absolute certainty of action, were required, to give them, with the advantages they possessed, decided superiority over the needle and other signal apparatus in use." By his improvements patented in 1858, he has "rendered this telegraph all that is required for practical use, combining certainty, speed, simplicity, durability, and portability." To avoid as far as possible more massiveness in moving parts than is required for strength, or for mechanical effects to be produced by inertia, an obvious enough principle, too often neglected by instrument-makers, or chronometer are more durable and more certain in their action than those of almost any larger machine comparable with it as to complexity, and Mr Wheatstone seems to have been impressed with this idea in designing the beautiful receiving instrument represented in the annexed figure, along with one form of "sender," adapted to work it, which, being electro-magnetic, requires no battery, and is complete as shown.
For the uses for which these instruments are chiefly intended, that is to say, for short lines of telegraph, with no specially trained telegraph operators to work them, these instruments seem to be almost perfect. The facility they afford for communication between different offices, departments, or stations of government, of national defences and field operations of an army, of law-courts, and of general, commercial, and manufacturing business establishments, can scarcely be over-estimated. It is to be hoped that, at least in all matters affecting the security of the country, and the efficiency of our army, in any part of the world, they will immediately be taken advantage of to the utmost.
6. The first type-printing telegraph was patented by Wheatstone in 1841. It was described as an application of the step-by-step letter-showing telegraph in the Companion to the Almanac for 1843, published by the Society for the Diffusion of Useful Knowledge, Oct. 1842, in the following terms:
"By substituting for the paper disc, on the circumference of which the letters are printed, a thin disc of brass cut from the circumference to the centre, so as to form four-and-twenty springs, on the extremities of which types or punches are placed, and adding a mechanism, the extent of which, acted on by an electro-magnet, causes a hammer to strike the punch against a cylinder, round which are rolled alternately several sheets of white paper and of the blackened paper used in the manifold writing apparatus, he has been enabled to obtain, without presenting any resistance to the type-wheel, several distinct copies printed of the message transmitted."
This telegraph was never brought into general use in Europe, but it was patented about seven years later in America, with various novel and ingenious mechanical details of execution, by Royal E. House of New York, and did the whole work of one of the three chief sets of telegraph lines of the United States for many years.
The general appearance of House's printing telegraph resembles that of a small cabinet pianoforte, with keys marked with the letters of the alphabet. The operator, in sending, commits his message to the line by touching the proper keys successively, and in an instant after his pressure on each key, the corresponding letter is printed at the same moment on two slips of paper, one running before his eyes and assuring him of the correctness of his work, and the other conveying his intelligence to be simultaneously read by the recipient at the distant station.
7. Hughes' American printing telegraph resembles House's in general appearance, and is similarly worked by means of keys corresponding to the letters of the alphabet, pressed by the operator. It is, however, essentially different from House's in the combination of electrical and mechanical arrangements by which it produces and indicates alphabetic signals. In House's telegraph the synchronous motion of two wheels—the sending contact-wheel turned by the operator, and the receiving wheel carrying the type—is produced, as in Wheatstone's printing telegraph, by the electro-magnetic escapement, worked by intermittent currents through the line, and is quite independent of any absolute uniformity of speeds or of average speeds, the time being perfectly given from one station to the other. In Hughes' the signals depend entirely on a somewhat accurate measurement of time at each station. At the sending station, battery applications are made at certain intervals of time, longer or shorter according to the letter to be signalled. At the receiving station the letter meant is discovered by measuring the duration of the interval. The Telegraph principle of this mode of signalling is well known, being, in using only fact, the same as that on which Morse's dot and dash alpha- bet is founded, with only this difference, that instead of just two distinct durations, giving two distinct signals, Mr Hughes employs 28 durations¹ to give 28 distinct signals, representing the 26 letters of the alphabet and two other symbols. The mechanism by which he carries out this system of signalling is remarkably novel and ingenious. It serves—(1) To make battery applications at the sending station, with intervals between them, definitely fixed by clock-work; (2) To measure, to a sufficient approximation by corresponding clock-work at the receiving station, the intervals of time between these successive battery ap- plications; (3) To record the measurement by a Roman type, printed on a slip of paper; and (4) To set the clock at the receiving station to agree with the other at the sending station, in the instant of completing the record of each measurement. One piece of clock-work for each station, serving for both the transmitting and the receiving appa- ratus, which are put together in one instrument, gives a rapid motion (amounting in some of the instruments to two turns per second) to a "type-wheel" moving round a hori- zontal shaft, and a transmitting arm carried round in the same period by a vertical shaft, geared to the former by bevelled wheels. This motion is regulated very accurately by an escapement and spring, as in a watch or chronometer, but vibrating at an unusually high degree of rapidity, 56 times to each revolution of the type-wheel. The annexed drawing will convey an idea of the general appearance of the instrument.
The "type-wheel" is so called from carrying, rigidly con- nected with it, the types of the different letters and signs to be singly signalled—28 in number. The paper which receives the message is brought up by mechanism started at the right instant by the signal current, so as to strike the type of the letter intended, and receive its impression as it passes. If the type is not quite exactly in the correct position, it is placed so by the mechanism for carrying the paper which, in the very act of becoming temporarily geared with the type-wheel, adjusts it, by making it slide round on its shaft (with which it is held in connection, not rigidly, but only by friction) until the teeth of the one piece fit perfectly into the hollows of the other. By this beautiful contrivance every error decidedly less than half the space from letter to letter is perfectly corrected each time an impression is made. Thus, during the use of the instrument to receive at one station, its type-wheel is kept in perfect agreement with the sending-wheel at the other station; and a wrong letter cannot, if the electric action keeps time, be printed unless the rate of the clock-work is at fault by some such amount as one or two per cent., which need never be the case. If the two wheels are allowed to run a long time without the electric maintenance of agreement, they will be found more or less at variance, as the pieces of clock-work, however good, cannot be perfect. All that is necessary to bring them into agreement is, to strike several times the key corresponding to a pre-arranged adjustment signal— that corresponding to the dot type, for instance. The re- ceiver knows (according to the regulated system of work- ing) that it is adjustment, not message, that is being sent; and he turns his type-wheel by hand till it prints dots. He then signals back "O. K." (the American telegraphic signal for "All correct!") and is ready to receive the mes- sage. If by any accident his type-wheel gets on a wrong letter in the course of a message, he disturbs the sender (who all the time sees the effect of his sending printed be- fore his own eyes) by sending back a few currents on him; he receives dots by way of acknowledgement, and resets his type-wheel to print dots correctly, and, therefore, also cor- rectly all that follows.
This system of telegraphic printing has a great advantage over the step-by-step system, in using continuous instead of intermittent currents, and so avoiding the necessity for the rapidly acting electric escapement, which, however skilfully planned and executed, is always liable to failure when worked too rapidly. Mr Hughes' instrument, in the purely chrono- metric system, on which it depends, takes advantage of a kind of mechanism in which accuracy and certainty have been attained to a degree which, for their present applica- tion, may be regarded as perfection; and in actual practice it appears to have proved a very decided superiority over all previous type-printing telegraphs, not only as to speed and accuracy, but in less liability to mechanical derange- ment by wear and tear, or by accident. Although brought out little more than two years ago, it is already in very ex- tensive use in America, where the advantages of telegraphs delivering their messages printed in Roman type, on paper ready to be put into the hands of the parties to whom they are addressed, have been more thought of than hitherto in Europe.
Mr Hughes' beautiful instrument involves many novel features and excellent inventions in each department—the receiving electro-magnet of peculiar construction and re- markable efficiency; the transmitting apparatus, with its contrivance to prevent unintentional repetitions of a letter through the operator holding his finger too long on a key; the printing apparatus, with the "corrector" alluded to above; the type-wheel lock for each station, to be opened by its own key, one of the letter keys of any of the instru- ments in the circuit. Of all of these the details are most interesting, and we regret to be obliged, by want of space, to leave them undescribed.
IX. ATLANTIC TELEGRAPH.
When a great experiment is made, the materials employed are generally lost, and knowledge is too often the only form of power acquired as the result. In the year 1857, as much iron as would make a cube of 20 feet side, was drawn into wire long enough to extend from the earth to the moon, and bind several times round each globe. This wire was made into 126 lengths of 2500 miles, and spun into 18 strands of 7 wires each. A single strand of 7 copper wires of the same length, weighing in all 110 grams per foot, was three times coated with gutta-percha, to an entire outer thickness of 4 of an inch; and this was "served" outside with 240 tons of tarred yarn, and then laid over with the
¹ Hence Mr Hughes' instrument, although capable of working at an extremely high speed through lines in which inductive embar- rassment is not felt, cannot possibly be adapted to give rapid signalling through a long submarine line. Atlantic 18 strands of iron wire in long contiguous spirals, and Telegraph passed through a bath of melted pitch. In August of that year, about 4th of the entire length of this compound rope was laid from the Irish shore westwards, and lost by a breakage at the stern of the Niagara. The remainder was conveyed in the two ships to Devonport, and stored for the winter in Keyham dockyard. A length of 55 miles of the portion which had been lost was lifted in tolerably good condition a few months later. During the ensuing winter and spring, about 900 miles more of similar cable were manufactured; and in the months of April and May 1858, the whole length of 3000 British statute miles was shipped on board H.M.S. Agamemnon and the U.S. steam frigate Niagara. After an experimental cruise in the Bay of Biscay, to test the appliances for laying the cable by actual trials in water 2500 fathoms deep, and some slight alteration of the machinery made in consequence on returning to Plymouth, the two ships, accompanied by H.M.S. Valorous and Gorgon, paddle-steamers—the former tender to the Agamemnon, the latter to the Niagara—set out for the middle of the Atlantic on the 10th June. After three unsuccessful, but not discouraging attempts, in which between 400 and 500 statute miles of cable were lost, the ships returned from the different points they had reached, to rendezvous in Queenstown harbour, where, on the arrival of the Agamemnon on the 12th July, the whole squadron were again together, and remained long enough to take in coal and make other requisite preparations for a final attempt. On the 17th July they again put to sea westwards. On the 29th they met at the mid-ocean rendezvous, joined the ends of the cable between the two ships bearing it, and commenced laying it in 2400 fathoms water, the Niagara continuing westwards, and the Agamemnon returning to the east. This time no accident stopped the continuous paying out; and on the 5th of August the two ships cut the cable, and left the ends on shore on the two sides of the Atlantic. The possibility of laying an electric cable across 2000 miles of ocean, in depths of from 1800 to 2500 fathoms—seriously doubted by nearly all practical engineers, and considered a perfectly chimerical project by some of the most eminent—was thus triumphantly demonstrated. The risk of failure in future attempts was brought almost within the limits of a common "sea risk;" the weather having been by no means favourable, especially on the Agamemnon's side, where, during three days of the six, strong breezes from several quarters were experienced, and at one time a fresh gale of head-wind. The telegraphic operations performed between Valencia and Trinity Bay during the remainder of the month of August will render the year 1858 ever memorable in the history of the world.
The world's news was read on the same day in the capitals of Europe and America. Question and answer passed freely, and friendly conversation was held, between the operators on the two sides of the Atlantic. The Queen of England and the President of the United States interchanged congratulatory messages, and assurances of mutual good-will on the part of the two great nations under their authority. One short message saved thousands of pounds of money, and an inestimable amount of anxiety, by giving timely notice of an accident, which disabled one of the Transatlantic steamers off the American coast, bound for England. Another—nearly the last utterance of the failing cable—countermanded two British regiments under orders to embark, and prevented them from leaving the American colonies on a bootless voyage across the Atlantic.
The last words of the Atlantic telegraph were read at Valencia on the 20th October 1858—"two hundred and forty t-k (? two).—Daniell's now in circuit." The full message—as was afterwards learned in the old, and alas! at this moment, the only way of receiving intelligence from the other side of the Atlantic—was "two hundred and forty trays" and seventy-two liquid Daniell's now in circuit." This prodigious power, one thousand times as much as would have given perfect signals to the mirror galvanometer in use as receiving instrument at Valencia through the same cable, if ordinarily well insulated, proved insufficient for continuing telegraphic work, and it became certain that only mending the insulation in one or more faulty places could restore communication. Before the process of laying was complete, indications of very defective insulation had been given by the readings of the "marine galvanometer" recorded on board each ship. After the ends were landed, the insulation became farther deteriorated; every attempt to establish communication by means of the regular telegraphic instruments prepared for the use of the company proved a failure; and it was only by the introduction of the mirror receiving instrument on each side of the Atlantic that an interchange of intelligence was effected.
As soon as messages began to come from Newfoundland, they were read with very great ease at Valencia on the new system. At Newfoundland, on the other hand, three days passed, during which messages, continually being sent from Valencia, were not read or even recognised to be signals at all; and it was only by the occasional introduction of the mirror instrument into circuit, in accordance with instructions given at Devonport to special operators sent out in charge of it, that the first words were read on the other side of the Atlantic. A "detector," or common telegraph galvanometer, of a kind then much used by British practical electricians, was next tried, and it was found possible to read by it, although with great difficulty (the signal deflections scarcely amounting to half a degree), and only at an excessively slow rate (half a word per minute or less); but when, as was often the case, these attempts failed altogether, the mirror was had recourse to, to see whether any message was coming or not. Matters were conducted in this unsatisfactory way at the Newfoundland station for about a week after the first words had been read, until the mirror was permanently introduced into circuit and regularly used as receiving instrument, in accordance with an order transmitted through the cable from Valencia on the 21st of August. From that time forward the messages were read with about equal ease at the two ends; but the days of the first Atlantic Telegraph were numbered. On the 1st of September it conveyed the two military messages. On the following day it conveyed one congratulatory message for a public meeting in New York, addressed to Mr Cyrus Field, to whose untiring energy it in a great measure owed its existence; and it failed to convey a second similar message on the same day. From that time till its death-struggle, on the 20th of October, it was silent.
And now that splendid combination of matter lies on the bottom of the Atlantic, its Newfoundland end irrecoverably lost. A few miles of it—possibly 200 miles—may be lifted from Valencia, and used for some minor telegraphic work, perhaps cut up into target telegraphs; but its value can scarcely, if at all, exceed the expense of lifting it. L375,000 have been spent in the great work; and the world, if not the sub-
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1 A form of battery introduced by the writer of this article for nautical and land telegraphic use, which has the good electric qualities of the Daniell's, without the disadvantages inseparable from the use of porous cells. It consisted of copper trays, each strewed with crystals of sulphate of copper covering its bottom, and filled with sawdust moistened with sulphuric acid and water, on the top of which an amalgamated zinc plate was laid. These trays, thus charged, were piled one with its outside copper bottom on the top of the zinc of another, in columns of from five to twenty, after the fashion of an old voltaic pile. The writer has since made many trials of different forms, and has been led to plan, with the assistance of Mr F. Jenkin, an improved "Sawdust Daniell's," from the use of which, in various applications, he anticipates much advantage. Reverting to the general view of the telegraphic art with which we commenced this paper—the art of interchanging ideas between two intelligent beings by means of inanimate matter occupying space between them—we see that in all its departments we have to deal solely with symbols and with combinations of symbols.
The physical science on which any branch of the art is founded is occupied with the dynamical action in the matter, by which the indications of these symbols are conveyed from one being to the other. The purely mathematical science of combinations constitutes the foundation of that large part of the telegraphic art in which distinct successions of signals are arranged for expressing the inconceivably great although finite number of ideas which can be communicated on any finite system, and which is in fact the art of language. The marvellous and varied development which this art has received among all races of men from the beginning of the world, presents an extremely simple and uniform problem for the special telegraphist—to produce in arbitrary succession a certain very limited number of symbols, twenty-six or thereabouts, for the letters of the alphabet, and a few others which it is convenient although not necessary to include.
The various electro-telegraphic methods to which we have referred, contain remarkably varied solutions of this problem. In the first and in the last which we have mentioned, each letter is indicated by one physical element, measured out at the sending station to indicate the letter to be conveyed, and tested by measurement at the receiving station to discover what letter was meant. In the first method, the strength of an electric current is the indicating element; in the last, it is an interval of time. Thus, in the first we have an alphabet of strengths—
\[1, 2, 3, \ldots, 26;\]
or
\[-13, -12, -2, -1, +1, +2, \ldots, +12 + 13.\]
The measuring out at the one end, and the testing by measurement at the other, have been shown by the writer to be practicable with ease and certainty. It is obvious that no other method can give the same speed. The variable insulation of air-lines and of imperfect submarine lines constitutes the sole objection to its universal application; the "earth currents," which it had been supposed by some would prevent its success, having been found by the writer to exercise, in the Atlantic at all events, no influence which cannot be perfectly and easily compensated or allowed for, except on rare occasions of unusual disturbance.
In the last method, the basis of Hughes' printing telegraph, we have an alphabet of simple durations—
\[1, 2, 3, \ldots, 26;\]
where the unit is an interval of time, a small fraction of a second, when rapid working is required.
In all the other methods, the letters of the alphabet are compounded of successions of simpler signals. Thus, in the Steinheil system (the old single needle, the Highton, and the most recent recording system of Wheatstone's, all included), we have the \(+\) signal, and the \(-\) signal, and we have pauses of shortest duration (between the signals composing a letter); pauses of medium duration, to distinguish the succession of signals constituting one letter from the succession constituting the next; and, though not essential, pauses of still longer duration to mark the ends of words. This system, therefore, involves essentially strengths and durations in its elementary signals.
The Wheatstone step-by-step telegraph, including its applications by the French to mimic semaphore forms, and by its inventor and the Americans to printing, is a telegraph of simple durations, as is also the Morse system in all its varieties.
Thus all the systems of Class II., according to our previous division, are founded on purely chronometric signals, while the practical systems of Class I. involve a chronometric along with a galvanometric principle. It comes to be a question of high interest, and possibly of practical importance, Can a purely galvanometric system be founded on the data of Class I.—that is to say, on means of producing, and of distinguishing when produced, three different degrees of current? The answer to this question will be obvious as soon as its meaning is perfectly understood, but this cannot be until the true nature of a perfectly elementary signal, as defined above, is examined for the particular modes of working available. If we work by induction coils, the "change" constituting a signal is from the natural zero, or galvanic or earth current in the line, to what can be produced and tested as having been produced, by either a positive or a negative electro-magnetic impulse. Thus we have just two simple signals; and it is perfectly felt, by the receiver as well as the sender, that the rise and fall of current consequent on each impulse is in truth just one signal, and to be reckoned as one change constituting the whole effect of one operation. Hence very obviously two simple signals constitute the purely electric elements of the positive and negative electromagnetic signals, which we may denote, for facility of reference, by the symbols \(a, b\). If, on the other hand, we use a galvanic battery, worked by a key with three positions, or by the double key sketched above (VII. 4), a signal made in the usual manner (by means of the double key, for instance, by pressing down either spring, holding it for a short time, and then releasing it) is essentially a double signal, consisting of two operations following one another, with an arbitrary interval of time between them. A truly simple signal on this system is produced by a change of the finger from not touching the key to pressing either spring, or from one spring to the other, or to neither. Now, whatever be the position of the finger at any instant, there are only two ways in which it can be changed, and therefore, in reality, there are just two arbitrary distinct signals available; and the same holds clearly for any mode of producing and repeating successively, in any order, three different strengths of current. Thus, let the three strengths (which may be respectively negative, zero, and positive) be indicated by the numbers 1, 2, 3. Then the two distinct signals will be—
Signal \(a\).
From 1 to 2;
or
From 1 to 3;
Signal \(b\).
From 1 to 2;
or
From 1 to 3;
or
From 2 to 1;
or
From 3 to 2.
The question we put will be now answered in the affirmative if we can make a sufficient alphabet out of two distinct signals, without pauses of time to mark the separate successions. This may clearly be done in two ways—
1. We may retain one of them to indicate a division, and use repetitions of the other to indicate letters. The alphabet on this principle would stand as follows:—
\[E = a\beta\] \[T = a\alpha\beta\] \[I = a\alpha\alpha\beta\]
and so on, the shortest compound symbols being chosen for the most frequent letters. This alphabet, worked by electro-magnetic impulses, would differ from the signal foundation of the step-by-step system only in substituting a negative for a pause of time to mark the beginning of a new letter. It would have scarcely an appreciable advan- Atmospheric and Terrestrial Electricity
The earth is a conductor, surrounded by air, which is one of the best of insulators when not tried by too strong electromotive force. The earth is, on the whole, negatively electrified; different strata, or portions of the air, are electrified, some negatively and some positively, which, as carried about by the wind, and changed in shape by ascending and descending aerial currents, keep always, even in the most serene weather, inducing great changes in the electrification of the earth's surface at any locality. Falls of rain, hail, and snow are nearly always accompanied by strong and variable developments of atmospheric electricity, which produce inductively, and probably also by convection, in the course of a shower, rapid changes of degree, and most frequently also transitions from negative to positive and back, in the electrification of the earth's surface in the neighbourhood. When electromotive force becomes so intense in any part of the air as to break down its insulating power, a discharge (lightning) takes place, either between electrified masses of air and the earth, or between two masses of oppositely electrified air, and produces instantaneous change in the superficial electricity of the earth.
All these changes, gradual or sudden, in the deposits of electricity on the surface, require currents through the interior, to fulfil the actual conditions of tendency to equilibrium. The whole quantity of electricity thus flowing through the earth at any time cannot, in general, so far as the writer can judge, be sufficient to produce any sensible current in a submarine wire, or a perfectly insulated air-wire, connecting two metal plates buried in different localities. On the other hand, actual telegraph wires stretched high in the air, from pole to pole, have their aerial insulation constantly broken, either by disruptive discharges ("electric brushes," or "St Elmo's fire"), or by convection of watery or other particles flying away from contact with them. They therefore keep constantly "collecting" atmospheric electricity like Beccaria's "exploring wire," and sending it down (as by his "deferent wire") into the telegraph stations, and through the coils of the receiving-instruments to the earth, producing currents almost always sensible to a delicate galvanometer, not unfrequently strong enough to interfere with signalling, and, during thunder-storms, sometimes melting the wires and destroying the instruments.
Want of space prevents us from describing means which have been adopted for guarding against such accidents.
Electricity is never found quiescent except for an instant at a time, in an insulated wire connecting two copper plates buried in the earth, or sunk in the sea, at any considerable distance asunder. A galvanometer, if placed in any part of the line of conduction, always indicates a current in one direction or the other, except at instants of transition through zero. The strength of this current is always varying,—in general, gradually from minute to minute: on some extremely rare occasions it changes so abruptly as to throw the galvanometer needle into vibration. A day seldom if ever passes without the direction of the current changing several times; but no relation has yet been discovered between the times of such changes and either solar or lunar hours. These "earth currents," as they are called, have been observed in all submarine cables, but as yet they have been only very imperfectly studied.
In the failure of the Atlantic cable in September 1858, the portion terminating at Valencia came to give nearly the same indications as an insulated conductor about 270 miles long, laid out westward, and connected with a copper plate sunk at a little less than that distance in the Atlantic. In these circumstances, the writer found that from one to nine or ten twentieths of the electromotive force of two Daniell's elements was generally sufficient to balance the earth-current; not unfrequently 14 or 15 were required; sometimes, although very rarely, 20, or the full electromotive force of two elements, was insufficient; and once or twice, in the course of the month of September, earth-currents were received so strong that five or six Daniell's elements would have been required to balance them.
Earth-currents are certainly related to the irregular variations of terrestrial magnetism, since they are always found unusually strong during brilliant displays of aurora borealis; for it has long been known that, on these occasions, the magnetic disturbances are unusually strong. Being related to the variations of terrestrial magnetism, it is probable that the earth-currents also will be found to have daily periods; but, in the meantime, we only know that, while the diurnal variation in terrestrial magnetism is observable in general every day, and is only on rare occasions overborne by irregular disturbances, the earth-currents vary each day from hour to hour, like the wind, under some overpowering non-periodic influence, and can only show daily periodicity in residual averages derived from lengthened series of observations. It is probable that careful synchronous observations of aurora, earth-currents, and variations of terrestrial magnetism, will lead to a discovery of the primary influence, whether in the earth, or terrestrial atmosphere, or surrounding interplanetary air, which causes these phenomena.
(w.t.)