as the word imports, is the art of printing by types; but it is likewise used to signify the multiplying of copies by any mechanical contrivance. Of the art of printing by types, and the many improvements from time to time either made or attempted in it, a pretty full account will be found in the *Encyclopaedia*, under the titles **Letter**, **Logography**, and **Printing**; and in this Supplement under the word **Painting**. Of typography, in the other and larger sense, some account may likewise be found in the *Encyclopaedia* under the title **Method of Copying Writing**; but to almost all these articles there is ample room for some additions here.

The *stereotype* printing of Didot and Herban, being considered in France as a great improvement, must not be passed over wholly without notice. The term *stereotype* is derived from the Greek words *εικόνα* and *τύπος*, because in this method the types are fixed and immovable in the form, so that none of them can be pulled or displaced by the pressman. We need hardly observe, to those who are at all acquainted with the history of printing, that the project of soldering a whole form together, or of casting a solid form from an impression made by a general system of types, or page ready composed, is not new. It was realized 70 years ago by William Ged, a goldsmith in Edinburgh; for an account of whose method we refer the reader to his life in the *Encyclopaedia*. Didot now follows nearly the same process as Ged. He does not indeed cast his types in a mass, but after the form is composed and carefully corrected, he cements or folders the types together so firmly that none of them is liable to be loosened by the action of the press or the adhesion of the balls. How far this method of printing is of value with regard to books which are altered and improved in every subsequent edition, may, perhaps, be questioned; but on a loose consideration of the subject, it seems as if it would, in every case, be advantageous to a bookeller to print a few copies of a work, and keep the types standing to print others as they may be wanted; —we say it would be advantageous, if it were not for the immense value in types, which would, by that means, be locked up. To form some judgment of this, it may be stated, that the works of Virgil, printed by Didot, in 18mo, form a beautiful volume of 418 pages, of 35 lines each. The character range for line with that called burgess, No. 2, in Caslon's book of specimens, the face of the letter being rather smaller; and we are told * that the price of the plates of this work is twelve hundred francs, or 50l. sterling. From this fact some judgment may be formed of the commercial question. We have casually looked at different books printed by Didot, but can say nothing of their correctness; the page is very pretty.

For multiplying copies of any writing, or of a book of ordinary size, Roehon, of the French National Institute, and now Director of the Marine Observatory at the port of Brest, invented, about the year 1781, a machine for engraving, with great celerity and correctness, the pages of the book or manuscript on so many plates of copper. It was submitted to the examination of a committee of the Royal Academy of Sciences, whose report of its utility was given in the following words:

"This machine appears to us to unite several advantages. 1st, Engraved editions of books may be executed, by this means, superior to those which can be made by the hand of the engraver, however skilful; and these engraved originals will be made with much more speed, and much less expense. 2d, As this machine is portable, and of no considerable bulk, it may become very useful in armies, fleets, and public offices, for the impression of orders, instructions, &c. 3d, It possesses the advantage which, in a variety of circumstances, is highly valuable, of being capable of being used by any man of intelligence and skill, without requiring the assistance of any professional workman. And, lastly, it affords the facility of waiting for the entire composition and engravings of a work before any of the copies are pulled off; the expense of plates, even for a work of considerable magnitude, being an object of little charge; and this liberty it affords to authors, may prove highly beneficial in works of which the chief merit consists in the order, method, and connection of ideas."

Roehon's machine consists of two brass wheels *, placed on the same axis above each other, and separated XLVI., by a number of pillars, each two inches in length. These two wheels, with the interval which separates them, are equivalent to a single wheel about three inches thick. In order therefore to simplify the description, they are considered as a single wheel which moves freely on its axis.

This wheel is perforated near its circumference with a number of square holes, which are the sheaths or sockets through which a like number of steel punches, of the same shape, are inserted, and are capable of moving up and down. They are very well fitted; and from this circumstance, as well as the thickness of the double wheel, they have no shake, or side motion, independent of the motion of the wheel itself. Every punch is urged upwards by a separate spring, in such a manner, that the wheel armed with its characters, or steel types (the lower faces of the punches being cut into the figures of the several letters), may turn freely on its axis; and if it be moved, the several punches will pass in succession beneath an upright screw, for pressure. The screw is fixed in a very firm and solid frame, attached to the supports of the machine; and by this arrangement a copperplate, disposed on the table, or bed of the apparatus, will receive the impression of all the punches in succession, as they may be brought beneath the vertical pressing screw, and subjected to its action.

But as the press is fixed, it would necessarily follow that each successive impression would, in part, destroy or mutilate the previous impressions, unless the plate itself were moveable. It therefore becomes necessary that the plate should be moveable in two directions: the first, to determine the interval between the letters and words, and form the lines; and the other motion, which is more simple, because its quantity may remain the same through the whole of a book, serves to give the interval between line and line, and to form the pages.

It will easily be conceived that it would be a tedious operation to seek, upon the circumference of the wheel, each several character, as it might be required to come beneath... beneath the press, because it is necessary to repeat this operation as many times as there are characters in a work. The author has considerably diminished the time and trouble of this operation, by fixing upon the axis of the great wheel, which carries the punches, another small wheel, about four inches in diameter, the teeth of which act upon a rack, which carries a rule moving between two sliders. This rule, or straight line, will therefore represent the development, or unfolding of the circumference of the wheel which causes it to move, and will show the position of the great wheel, which carries the punches. For these two wheels being concentric, the development of the small toothed wheel, of about two inches radius, will exhibit, in a small space (for example, that of a foot), an accurate register of the relative positions of the punches with regard to the pressing-screw. To obtain this effect, nothing more is necessary than to place a fixed index opposite to the moveable rule, which last is divided in the following manner:

The punch on which the first letter of the alphabet is engraved, must be brought under the centre of the pressing-screw; and a line of division then drawn upon the moveable rule, to which the letter itself must be added to distinguish it. The index, already mentioned, being placed opposite, and upon this first division, will serve to place immediately beneath the pressing-screw the punch, or rather the character, corresponding with the division upon the rule, without its being afterwards necessary to inspect the place either of the punch or the screw, with regard to each other. Consequently, as soon as the divisions which correspond with all the punches inserted in the wheel are engraved upon the straight rule, the fixed index will immediately determine the position into which that wheel must be brought, in order to place the punches under the pressing-screw in the order which the work may require.

This register, for this name distinguishes the rule and its index, has no other function in the machine than to guide the hand of the operator, and to show when the punch is very near its proper position beneath the pressing-screw. When this is the case, the required position is accurately obtained by means of a detent or catch.

The detent which he uses for this operation is a lever with two tails, one of which is urged toward the circumference of the wheel by a spring. To this extremity of the lever is fixed a piece of hardened steel, of the figure of a wedge, which, by means of a spring, is pressed towards the axis of the great wheel; but may be relieved, or drawn back, by pressure on the opposite tail of the lever, so as to permit the great wheel to revolve at liberty.

In the next place, it must be explained how this detent takes hold of the wheel, so as to retain it precisely in the situation necessary to cause any one of the punches, at pleasure, to give its impression to the plate. For this purpose there are a number of notches cut in the circumference of the wheel, for the purpose of receiving the detent. These notches may be about half an inch deep, wider towards the circumference than elsewhere, and it will be of advantage that this outer width should be as great as the circumference of the wheel can conveniently allow. By this contrivance, the wedge will not fail to present itself opposite to one of the notches into which it will fall, and draw the wheel exactly to its due situation, even though the index of the register should not be brought precisely to the line of division appropriated to any particular letter. For if this last degree of precision were required in working the machine, it would be very prejudicial to the requisite speed which, above all things, is required in its use. When the wedge is therefore left at liberty, it not only enters immediately into its place, and moves the wheel till its two sides apply fairly to the interior surfaces of the notch, but retains the wheel in this state with the necessary degree of stability.

The method of giving the proper figure to these notches is very easy. For this purpose it is necessary, in the first place, to impress all the characters contained in the wheel on a plate of copper or pewter. The support on which the plate is fixed must be moved in a right line, after each stroke of the punch, through such a space that the characters may be arranged one after the other without touching. Now, as the perfect linear arrangement (supposing every part to be true) must depend on the notches, it might seem insufficient to cut them according to the method used for the wheels of clock-work; but as it is very difficult to avoid some obliquity on the face of the punch, and perhaps in the hole through which it passes, it is in almost every case necessary to retouch the notch itself. The requisite degree of precision may be easily obtained, when, upon examining with attention the print of the characters engraved upon the plate, the inequalities shall have been ascertained by a very fine line passing exactly under the base of two similar letters, assumed as objects of comparison: for the irregularity of linear position may, by this means, be determined with great exactness, and remedied to the most extreme nicety. In this operation, the workman must file away part of that surface of the notch which is opposite to the direction of the motion the character requires. Great care must be taken to file only a small portion at a time, in order that the infant may be seized at which the wedge, by entering into the notch, brings the character to its due situation.

These details, respecting the right-lined arrangement on the characters, must not divert our attention from the very great celerity with which any letter is brought to its place under the press by means of the register and detent. This celerity is an object of so much importance in the engraving of a great work, that every means ought to be pursued which may tend to increase it. For this reason it is, that instead of following the alphabetic order in the arrangement of punches on the surface of the wheel, we ought to prefer that in which the sum of the different motions to be given to the wheel, for engraving an entire work, shall be the least possible. This tedious enquiry may well be dispensed with, by observing the order in which printers dispose their cases of characters, that the letters of the most frequent recurrence may be most immediately under the hand of the workman.

If all the characters afforded an equal resistance to impression in a plate of metal, a constant force would never fail to drive the punches to the same depth. But the faces of the letters are very unequal, and consequently it will be necessary to use a variable force. Most workmen use the hammer, and not a screw, as in this This machine, for stamping. If the hammer had been used in this machine, it is evident that if we supposed it to have fallen from the same height upon every one of the punches, the force of the stroke could be rendered variable according to the nature of the characters, by placing a capital, or head, upon each, of an height properly adjusted to receive the hammer after passing through a greater or less space. But the heads of our punches are variable at pleasure, because they are screwed on; and thus it is that, by experimentally adjusting the heads of all the punches, a set of impressions are obtained of equal depths from every one of them. When, for example, the letter i is placed under the hammer, the upper part of its head is at a small distance from the head of the hammer, in order that its fall, which begins always at the same place, may strike this letter weakly; but when the letter M is brought under the hammer, the upper part of its head being much less elevated than that of the letter i, will receive a much stronger blow. The impressions of the letters M and i will therefore always be equally deep, if the heads of the punches be once properly fixed by experiment.

Instead of the stroke of a hammer, however, our author makes use of the pressure of a screw, of which the threads are so inclined that it runs through its female socket, and would fall out merely by its own weight. This construction affords the double advantage of preserving the impressions from the effects of the circular motion, and of affording a fall in the screw of nearly nine lines for each revolution. The head of this screw is solidly fixed in the centre of a brass wheel, of which the position is horizontal. The diameter of this wheel must be sufficiently large, that its motion may not be perceptibly affected by the irregularities of friction in the screw. This considerable diameter is also requisite, because the pressure of the screw depends not only upon the force which is applied, but the distance of the place of application from the centre of movement.

It is essential that this wheel should have very little shake; for which reason it is advisable that the axis of the screw should be prolonged above the wheel itself, that it may slide in a socket firmly fixed to the frame of the machine. In this situation, the wheel, which is fixed on the prolongation of the screw, will have its plane constantly preserved in a situation parallel to itself, without any libration, notwithstanding the rise and fall of near nine lines, or three quarters of an inch, which it undergoes for each revolution on its axis.

It has been stated, as a requisite condition, that the screw should constantly fall from the same fixed point, or elevation, upon the heads of every one of the punches. To accomplish this essential purpose, a lever is finally fixed to the support of the screw; which lever resembles the beam of a balance, having one of its extremities armed with a claw, and the other serving to give it motion through a small vertical space. The claw falls into a notch in the upper surface of the wheel attached to the screw, as soon as that wheel has risen to the desired elevation; and the lever itself is so far limited in its motion, that it cannot take hold of the wheel, excepting when it has reached that height. The wheel, therefore, remains confined and immovable, by means of this detent, and cannot descend until it is delivered by pressure upon the opposite tail of the lever. In this machine, the wheel which has the pressing screw for its axis does not perform an entire revolution. It was with a view that there might never be any fall capable of shaking and disturbing the machine that the author determined to use only two-thirds of a revolution to finish those punches, which afford the strongest resistance. The screw consequently falls only through five lines upon those heads which are least elevated, and about two lines upon those which stand highest. Whence the difference between the extreme heights does not exceed four lines.

It is obvious, that so small a difference is not sufficient to strike all the characters from M to the letter v, when the wheel which governs the screw is put in motion by a constant weight, of which the impulse, like that of a hammer, is increased only by the acceleration of its fall. It is evident that this requisite variation of force might be had by changing the weight; but it is equally clear, that the numberless and incessant changes which the engraving of an entire work would demand, would be incompatible with that degree of speed which forms one of the first requisites. He was therefore obliged to render the force of the weight, which turns the screw, variable, by causing it to act upon levers of greater or lesser lengths, according to the different quantities of impulse required by the several punches. For this purpose he adopted the following construction: He connected by a frail chain to the wheel, which moves the screw, another wheel, having its axis horizontal, so that the two wheels respectively command each other. They are of equal diameter, and the chain is no longer than to make an entire turn round each wheel. This second wheel, or leading pulley, is intended to afford the requisite variations of force, which it does by means of a frail fixed upon its axis. The frail is acted upon by a cord, passing over its spiral circumference, or groove, and bearing a weight which is only to be changed when a new set of punches for characters of a different size are put into the great wheel. The spiral is so formed, that when the weight descends only through a small space, the part of the cord, which is unwound, acts at a very short distance from the centre of the pulley; but when the fall is greater, the part of the frail upon which it acts is so far enlarged as to afford a much longer lever, and, consequently, to give a proportionally greater effect to the stroke. This construction, therefore, by giving the advantage of a longer lever to a greater fall of the screw, affords all the power which the nature of the work, and the different spaces of the letters demand.

The support on which the plate is fixed must, as has before been remarked, move to as to form straight lines. This motion, which serves to space the different characters with precision, is obtained by means of a screw, the axis of which remains fixed, and carries a female screw or nut. The nut itself is attached to the support of the metallic plate, which receives the letters, and carries it in the right lined direction without any deviation; because it is confined in a groove formed between two pieces of metal. The screw is moved by a lever, which can turn it in one direction only, because it acts by a click upon a ratchet-wheel, which is fixed to the head of the screw. The action of this lever always begins from a fixed stop; but the space through which it moves is variable, according to the respective breadths of the letters. This new consideration induced M. Rouchon to fix upon the rule or plate of the register, a number number of pins, corresponding with the different divisions which answer to each punch; these pins determine the distance to which the lever can move. It therefore becomes a condition, that its position in the machine should be opposite to the fixed index which determines the character at any time beneath the pressing screw. The lever and its pin are therefore the sole agents employed to space the characters. If the plate were not moved by the lever, the impressions would fall upon each other; and thus, for example, the letter i would be totally obliterated by the impression of the letter l.

Whenever, therefore, it is required to dispose the letters i and l beside each other, the plate must be moved after striking the letter i through a space equal to the quantity of the desired operation. Suppose this to be one-fourth of a line, and that the lever should run through an arc of ten degrees to move the plate through this quantity; so long as the pin of the letter l shall be adjusted to the necessary length to enable the lever to describe an arc of ten degrees, the operation of spacing the two letters i and l will be reduced to that of placing the last letter beneath the fixed index, and moving the plate till the lever shall be stopped by the pin belonging to the letter l. All the other letters will be equally spaced, if the disposition of the punches in the wheel be such, that the last stroke of any letter shall confound itself with any letter of a single stroke, supposing them to be impressed one after the other, without moving the lever between stroke and stroke. This arrangement deserves to be very seriously attended to, because the process could not be performed without it.

Many well-informed persons are of opinion, that the perfect equality which this machine for engraving affords in the formation of letters and signs the most difficult to be imitated, may afford a means of remedying the dangers of forgery. It is certain that the performance exhibits a simple and striking character of precision, which is such, that the least experienced eyes might flatter themselves, in certain cases, to distinguish counterfeits from originals. Lavoisier, whom the friends of science and the arts will not cease to regret, made some experiments of this kind for the caisse de compter, which were attended with perfect success. Artists appointed for that purpose endeavoured in vain to imitate a vignette, formed by the successive and equal motion of a character of ornament.