A lamp is a contrivance for producing light by the combustion of such materials as are fluid at common temperatures, such as most of the fixed oils; the solid fats being made into candles. The kind of oil used for burning in lamps varies, in different parts of the world, with the sources of supply. Whale oil is used in Great Britain, but seal oil, fish oil, and oils obtained from seeds by pressure are also largely consumed. In Paris the oils of rape-seed, and of poppy-seed are used; and in the S. of France, and in Italy, an inferior kind of olive oil, and also the oil of the earth-nut are employed. In the latter country a lamp oil is expressed from grape-stones. In Piedmont walnut oil is common; oil of sesamum-seed is burnt on the eastern and southern coasts of the Mediterranean; while in tropical countries cocoa-nut oil, which is solid in the climate of Great Britain, is generally used. In China, the Camellia oleifera is cultivated for the sake of the oil obtained from its seeds, also a shrub, Croton sebiferum, the fruit of which yields a useful oil. In consequence of the deficient supply of tallow during the late war with Russia, inquiries have been set on foot in various parts of the world as to the seeds and other vegetable products from which oil may be obtained, and the result of these inquiries has already shown that many oil-yielding substances, not before known in commerce, exist. The export of oils from the East Indies, especially, gingelly, has greatly increased. Pistachio-nut oil is becoming common, as is also ground-nut oil from Africa. All these oils are used for burning in lamps.

Before a combustible can be made available for the purposes of artificial illumination, it must be decomposed in so regulated a manner that its hydrogen may furnish a steady flame, and its carbon the requisite amount of illumination; for which purpose the oil or fatty substance, whether in lamps or candles, must first be made fluid and then gaseous, the gaseous portion, resulting from the decomposition, by heat, of the fluid, filling the interior of the flame, combining with the oxygen of the surrounding air, and becoming dis- sipated as products of combustion, after having diffused both light and heat around. In a candle the combustible matter is rendered fluid by the heat of the flame, which forms the tallow just below it into a very perfect cup, which it keeps filled with liquid fat, and this is raised by the capil- lary attraction of the wick into the flame, where the che- mical changes take place which result in the production of light and heat. In a lamp a similar action goes on, only the fluid combustible matter is contained in a separate re- servoir, the position of which must be such as to cast as little shadow as possible. The simplest form of lamp con- sists of a thin layer of oil upon a quantity of water contained in a glass vessel, in which is floated a small brass cup, con- taining a glass tube, fitted by means of cork. The oil rises up the tube above the level on the outside, but when flame is applied to the top of the tube, the oil takes fire and burns with a small feeble flame; the fluid within the tube is depressed by the heat, and the pressure of the oil on the outside tends to overcome the depression, thereby maintaining the oil at the required height. If the tube exceed a capillary bore, the oil will not burn. In some cases, a waxed wick about an inch long is passed through the centre of a compound disk of cork and card, and this, with the cork undermost, is placed upon the oil floating on water in the glass vessel. This lamp, which gives a faint light, is called a veilleuse, and is sometimes used in France in bedrooms. Not more complex than this simple contrivance is the arrangement of the antique lamp (figs. 1, 2), which, with great artistic beauty of form, does not claim a higher con- struction than the lamp of many rude nations. It consists of a vessel, open or closed, with a wick rising through a hole in the beak; and as combustion can only take place on the outside of the flame, more carbon is likely to be liber- ated from the oil than the oxygen in contact with the flame can consume, hence such a lamp is always liable to smoke. In the old kitchen lamp the beak is removed a considerable distance from the reservoir, so as to diminish the shadow cast by the flame, and thus increase its illumi- nating power. Until the year 1789 (when Ami Argand invented the lamp which continues to bear his name) lamps were dull, smoky, ill-constructed articles, soiling every- thing around them, and filling the air with a nauseous odour.

The Argand lamp has undergone many improvements since the date of its invention. A common form of this lamp is represented in fig. 3, where A is the reservoir, which is air-tight at top, and has the neck immersed in oil, so that oil flows out of it only when the external air is ad- mitted to ascend through the neck; it contains a short column of liquid, from the top of which the pressure of the atmosphere is excluded, and therefore the column is sustained by the weight of the atmosphere pressing on its base, on the same principle as a bird-cage fountain. Oil is introduced into the reservoir A by taking it off and holding it with the neck uppermost. The sliding tube Q is pushed so as to cover the hole t, and the oil is poured in by a hole at the bottom, which at other times is closed by a screw-nut; when this is done, the reservoir A is re- placed in F, and secured by screwing it round. When the lamp is to be lighted, the hole t is opened by depressing the sliding tube by its handle Z, and the oil will flow out of A till it rise in F, and in the annular cavity that contains the wick, to the level of the top of the hole t. When the oil in F is lowered by the burning of the lamp, so that the sur- face of the oil in F is below the upper part of the hole, then a bubble of air ascends into A, and a similar quantity of oil descends into F, till the surface of the oil rises again to cover the upper part of the hole. It sometimes happens that the air in A is heated by the warmth of the room, and then too great a quantity of oil descends into F, in consequence of the expansion of the hot air in the upper part of A, so that the oil not being all consumed in the wick, falls down through the tube g, and may even run over from the cup P. This is an inconvenience attending the use of oil reservoirs of this construction. When the lamp is not burning, the hole t is closed by drawing up the sliding tube Q; the lamp may then be inclined, without making the oil descend from the reservoir. The cylindrical part, where the flame is pro- duced, is composed of three tubes d, f, g. The tube g is soldered to the bottom of the tube d, just above o, and the interval between the outer surface of the tube g and the inner surface of the tube d, is an annular cylindrical cavity closed at bottom, containing the cylindrical cotton wick im- mersed in oil. The wick is fixed to the wick tube h, which is capable of being moved spirally; within the annular cavity is also the tube f, which is capable of being moved round, and serves to elevate and depress the wick. P is a cup that screws on the bottom of the tube d, and serves to re- ceive the superfluous oil that drops down from the wick.

These figures are copied from the originals in the British Museum. Lamp along the inner surface of the tube \( g \). The air enters through the holes \( o, o \), and passes up through the tube \( g \) to maintain the combustion in the interior of the circular flame. The air which maintains the combustion on the exterior part of the wick enters through the holes \( m \), with which \( n \) is perforated. When the air in the chimney is rarefied by the heat of the flame, the column of the atmosphere, of which the chimney is the base, becomes lighter than the surrounding columns; and the surrounding columns, pressing with their excess of weight, enter the lower part of the chimney, and pass upward, with a rapid current, to restore the equilibrium between the adjacent columns of the atmosphere.

In some lamps, above the orifice of the tube \( g \), and nearly at the height of the top of the flame, there is placed a circular plate of metal, of the same diameter as the tube: this has the effect of turning the current of air into that part of the flame where smoke would otherwise be produced. The same effect is obtained by the contraction of the cylindrical glass chimney at \( R G \). See Gas-Lamp. The oil flows from the reservoir \( A \) and \( F \) through \( N \), and occupies the cavity between the exterior surface of the tube \( g \) and the inner surface of the tube \( d \). The oil rises in the annular cylindrical cavity between these two tubes to the level of the opening \( t \). The part \( k i \) is a short tube, which receives the circular wick, and slides freely on the tube \( g \). The tube \( g \) has a hollow spiral groove on its exterior surface, into which enters a pin connected with the wick-tube \( k i \). The wick-tube also has a catch, which works in a perpendicular slit in the tube \( f \); and, by turning the tube \( f \), the wick-tube will be raised or lowered, for which purpose a ring, or stage, \( r n \), fits on the tube \( d \), and receives the glass chimney \( R G \); a wire \( S \) is attached to the tube \( f \), and is bent over the edge of the tube \( d \), and descends along the outside thereof. The part \( r n \), that supports the glass chimney, is connected, by four other wires, with the ring \( q \), which surrounds the tube \( d \), and is capable of being moved round. When \( r n \) is turned round, it carries round along with it the ring \( q \), the wire \( S \), and the tube \( f \), and thereby produces the elevation and depression of the wick.

In the most simple construction of Argand lamps, the surface of oil in the oil-reservoir is nearly on a level with the flame, because the capillary attraction of the wick can only raise the oil a little above the surface of the reservoir. The surface of the reservoir also is considerable, that the lamp may burn for a sufficient length of time before it has consumed so much oil as to reduce the level of the oil below the reach of the action of the capillary attraction of the wick. Mechanists have contrived lamps of various forms, with the view of removing the inconvenience of the shadow of the reservoir, which cannot be got rid of in the common lamp with one lateral beak.

In what is called the Astral lamp, the oil vessel is of a flat annular shape, so that a tolerably large supply of oil may occupy only a small depth. The vessel surrounds the burner at the distance of a few inches, and is supported by two curved tubes, one of which conveys the oil to the wick. The shadow of this oil vessel, though small, is cast all around, and the two supporting tubes also cast their shadows on the table; but when the lamp is hung from the ceiling, the shadow of the oil-vessel may fall so as not to be inconvenient. In the Simulbra lamp (sine umbra, or without shadow), the shadow is greatly reduced by making the circular oil-vessel in such a way that its three surfaces meet in the form of a flat wedge, the sharp edge being directed towards the flame. The position of the flame, with respect to the oil-vessel, is such that two tangents drawn from the apex and base of the flame \( oo \) (fig. 4), meet a few inches behind it in a point, beyond which there is no shadow; and even within the space of the shadow the ground-glass shade which rests upon the oil-vessel, breaks up the shadow by its diffusion of the light: \( f \) represents the inner cylinder, with the spiral groove for raising the wick.

In order to get rid of the shadow, lamps have been constructed in which the oil-vessel is placed in the foot or pedestal, and the oil is raised to the wick by various ingenious contrivances. In Girard's lamp the oil is raised by the compression of air somewhat after the manner of water in a fire-engine, or as in Hero's fountain, where the pressure exerted in one vessel is transferred to another distant vessel by means of the compressed air. In Keir's Hydrostatic lamp, the oil is raised and supported by a column of salt and water, sufficiently dense to support a column of oil \( \frac{1}{2} \) of its own height. Instead of the solution of salt, other heavy liquids, such as syrup, honey, mercury, or a solution of sulphate of zinc may be used. The zinc solution is \( \frac{1}{57} \) times denser than oil, hence a column 10 inches high, will support a column of oil \( \frac{1}{57} \) inches high. The zinc column is fed from a reservoir, so as to maintain the oil at the proper level. Such lamps are subject to the great inconvenience of not being portable; indeed a very slight motion causes the fluids to oscillate and extinguish the flame. The principle of such lamps will be better understood by the following description of Mr Barton's lamp, in which \( T \) (fig. 5) is the oil-reservoir, from which the oil passes upwards to the wicks \( a, a, a \). The oil-reservoir is open at bottom, at \( h \). This is preferable to the mode of making the reservoir with a perforated bottom that screws off for the purpose of cleaning it. The fluid \( B \), in which the oil-reservoir is immersed, is a solution of salt in water. This liquid is contained in a vessel \( R M O \), which can be unscrewed at \( O \), for the purpose of taking out the oil-vessel. \( N \) and \( Y \) are two floats fixed to the oil-reservoir and its tube. The column of the solution of salt, \( c b \), presses against the oil at the open bottom of the reservoir, and maintains a column of oil in the tube to the height \( e \); to this point \( e \) the wick descends, and raises the oil to the flame by the capillary attraction of its fibres. The specific gravities of the oil and the solution of salt must be inversely as the heights \( ch \) and \( ke \); that is, the specific gravity of the solution of salt must be made to bear to the specific gravity of the oil the same proportion that the perpendicular height \( ch \), bears to the perpendicular height \( ch \). As the oil is consumed, the salt water enters the hole at the bottom of the oil-vessel; the surface of the water at \( c \) sinks, and the oil-reservoir, with the tube and wicks attached to it, sink also. The upper part of the vessel \( R \) should be of a capacity a little less than the capacity of the oil-reservoir, so that, when the water has displaced the oil, and filled the oil-reservoir, the float \( Y \) may be at the bottom of the enlarged part of the water-vessel \( R \). To prepare the lamp, the exterior vessel is filled with the solution of salt by the opening at \( t \); the solution passes into the oil-vessel by the open bottom \( h \), and the oil-vessel rests on the bottom of the exterior vessel. The oil is then poured in through the tube \( e \). The oil passes into the oil-reservoir, expels the water, and floats the oil-reservoir, raising the surface of the water in \( R \).

Attempts have been made to get rid of the leading objection to hydrostatic lamps by placing a pumping apparatus in the oil reservoir in the pedestal, but as the pump has to be worked occasionally by hand, this is an objection. In Carcel's Clock-work or Mechanical Lamp, the oil is raised by clock-work in such quantity as to exceed that consumed during the time of burning, the excess constantly flowing back into the reservoir over the outside of the burner, thereby keeping the metal work cool, and thus preventing the formation of carbon on the outside of the burner: the wick must be raised higher than in ordinary lamps. Modifications of this lamp have been introduced, in which the clockwork is replaced by a descending weight, such as a piston in a cylinder, or by causing a spring to act upon a piston. In such examples it has been found difficult to regulate the supply of oil to the wick. In Meyer's Elliptic Lamp, a leatheren piston or valve is worked by a rack and pinion, the oil being contained in a cylindrical vessel in the foot. So long as the piston is above the bottom of the oil-vessel, it is pressed by a spiral spring, attached to the top of the lamp; between the coils of this spring, and passing air-tight through the piston, is a tube, terminating in a funnel-shaped mouth in the oil-vessel, and covered with a perforated dish for straining the oil. The oil is pressed up this tube to the burner, near which is a fine silver tube, surrounded by a cup of wire gauze, of tinned copper, for straining the oil from solid particles. This tube, which is only \( \frac{1}{6} \) inch in internal diameter, regulates the flow of the oil, and its length and bore are so proportioned to the force of the spring, as to bring up enough oil to feed the flame, together with a surplus quantity which overflows, and keeps the metal parts of the wick cool. The lamp is supplied with oil at a point above the spiral spring, and flowing down, it occupies a position above the piston. By winding up the rack-work with a key, the piston is lifted to the top of the oil-vessel; the ascension tube, with the burner attached, is next pushed down through the piston, whereby the oil occupies a position below the piston, which is forced down by the spring, and thus raises the oil. Such a lamp will yield a good light for eight or ten hours, and will allow of the combustion of crude vegetable oils.

In Parker's Economic or Hot-oil Lamp, the oil-vessel is situated above the flame, for the double purpose of throwing the shadow in an unobjectionable direction, and also for overcoming the consistency of crude whale oil, which requires to be made fluid by heat before it can be burned in common lamps. Fig 6 illustrates the construction of this lamp. \( R \) is the oil-vessel, consisting of a double cylinder of metal, surrounding the upper part of the chimney \( M \), from which the oil descends by the arm \( A \), to the burner. This arm has at its lower part a slide-valve \( D \), worked by a trigger \( TC \), on raising which the supply of oil can be cut off, and the oil-vessel removed for filling. The valve allows the oil to be introduced, care being taken to fill the reservoir completely, since any air left in it would expand by heat, and cause the oil to overflow. The glass chimney \( G \) rests on three points, which can be raised or lowered by a rack and pinion, by which means the flame is regulated, not by the motion of the wick, as in ordinary lamps.

The facility with which volatile oils are decomposed and give off their carbon, renders them in general unfit for burning in lamps, but where such oils are plentiful, they may be brought into use by being mixed with other substances, which diminish the percentage of carbon. Thus, in some parts of Germany, oil of turpentine is mixed with strong spirit of wine; such a mixture is burnt in a lamp of peculiar construction, consisting of a large oval reservoir, into which the burner fits tightly, and descends nearly to the bottom. The burner consists of a wide metal tube passing down another tube, which surrounds a loose cotton wick. At the top of the burner tube is a narrower tube, terminating in a knob, and just below the knob is a ring of small holes. A small cup surrounds the burner-tube, in which a small quantity of spirit of wine is burnt preparatory to using the lamp, and the heat thus excited causes a portion of the spirit mixture to issue from the ring of holes, in the form of an inflammable vapour, which being ignited, a crown of flames is formed, surrounding the metal knob, the heat of which continues the vaporization, and the lamp burns in this way without requiring further attention. The light thus produced is brilliant, but expensive. Lamps have been prepared in Great Britain for burning various preparations of hydro-carbon, alcohol, pyroxylic spirit, &c. Lamps without wicks have been formed for the combustion of naphtha, resembling in principle the German lamp above described. Camphine has also been much in request. This substance is prepared by distilling oil of turpentine over chloride of calcium, so as to get rid of water; it then contains 88-46 per cent. of carbon, the remainder being hydrogen, so that it is a powerful illuminating body. From the readiness, however, with which it is decomposed, considerable care is required in adjusting the supply of air; if there be not sufficient oxygen, large flakes of unconsumed soot escape into the room, and unless the camphine be carefully prepared, it is apt to give off an odour which produces headache. Under proper management, the camphine lamp yields a white and brilliant light.

During the late war, the managing directors of Price's Patent Candle Company contrived a kind of lamp stove, which they call the Crimean Army Store or Camp Lantern, and which was adapted for baking, for boiling, and for warming a tent. Its dimensions are 17 inches in height, 19 inches across the handles, and 15 inches from back to front, the weight being about 30 lbs. It consists of a square sheet-iron box, with a door and latch, a cover for the same, a baking pan, with a cover, two lamps, each with six wicks, trimmed with cocoa-nut oil, and there is also a loose grating. The directions are as follows:—For baking: Let the baking pan, with cover, rest upon the top ledges, put the cover on the stove, then place the two lamps upon the bottom grating, light the 12 wicks, and shut the door; in less than half an hour the stove will be at a proper baking heat. N.B.—By covering the top of the stove with a coat, blanket, or sack, you will get up the