LAMP,

A contrivance for giving light. Lamps were in general use amongst the Jews, Greeks, and Romans. The candlestick with seven branches, placed in the sanctuary by Moses, and those which Solomon afterwards prepared for the temple, were crystal lamps filled with oil, and fixed upon the branches. The lamps or candlesticks made use of by the Jews in their own houses were generally put into a very high stand on the ground. The lamps supposed to be used by the foolish virgins, in the gospel, were of a different kind. According to critics and [7:13:41]antiquaries, they were a sort of torches, made of iron or potters’ earth, wrapped about with old linen, and moistened from time to time with oil. (Matth, xxv. 1, 2.) The lamps of Gideon’s soldiers were of the same kind. The use of wax was not unknown to the Romans, but they generally burned lamps; and hence the proverb Tempus et oleum perdidi, I have lost my labour. Lamps were sometimes burned in honour of the dead, both by Greeks and Romans. The testimony of Pliny, St Austin, and others, have led many to believe that the ancients had the invention of perpetual lamps; and some moderns have absurdly attempted to find out the secret. The curious may read Dr Blot’s conjectures on the subject in the Philosophical Transactions, No. 166.

Lamps are usually fed by expressed oils from vegetable or animal substances. In Britain, whale-oil, boiled from the subcuticular fat of the whale, is used for common lamps.

Tallow is one of the most common substances employed for giving light. The spermaceti, which is found within the cavity of the cranium of the spermaceti whale, is also used. There is a substance resembling spermaceti, formed by the decomposition of the muscular flesh of animals in moist places, which has been employed. Bees’ wax, a vegetable substance collected by the bee, and which, in some of its qualities, resembles the essential oils, is one of the best materials for giving light.

In no region of the globe are human beings found to exist without a supply of oil derived from animals or from vegetables; and in the more fertile regions several different plants, peculiar to each region, are cultivated on account of the fixed oil which is extracted from their seeds by pressure. These oils vary in quality. The oils fit to be employed in food are the most valued. Of the rest, many have the qualities which fit them for burning in lamps.

At Paris, oil of rape-seed and oil of poppy-seed are clarified for the lamp by filtering through cotton wool, and other processes. In the south of France and Italy the inferior kind of olive oil is used in lamps, and sometimes the oil of the plant called Arachis hypogaea, or earth-nut. In Italy, lamp oil has been expressed from the stones of the grape. In Piedmont, walnut-oil is used for lamps. On the eastern and southern coasts of the Mediterranean, and in China, they use oil of sesamum seed, called in Arabic semsom. In tropical countries, cocoa-nut oil, which, in the temperature of Britain, is solid and white like tallow, is burned in lamps made of the shell of the cocoa-nut and of bamboo. Much of the oil used in China is obtained by expression from the seeds of the tree called by botanists Camellia oleifera, which is extensively cultivated for that purpose, as is the shrub called Croton sebi-ferunι, on account of the solid oil or tallow which the Chinese express from its fruit. Essential oils, extracted from plants by distillation, are too volatile, and, in consequence of their volatility, are too easily inflamed, to be used in lamps.

Petroleum and naphtha issue from the earth in several places, and these sources are generally in secondary strata, and originate from fossil vegetable matter, in a state approaching to that of pit-coal. A source of petroleum existed some years ago near Colbrook Dale, and there is one at St Catherine’s near Edinburgh. The greatest natural deposits of petroleum and bitumen are in the island of Trinidad, and in the Dead Sea in Judaea. Naphtha is the most liquid of the oils proceeding from fossil vegetable matter, and possesses qualities very fit for burning in lamps. It is employed for this purpose at Genoa, where the streets are lighted with naphtha from Amiano in the adjacent territory. Naphtha, obtained in the state of a clear, colourless liquid, by distillation from pit-coal, has of late been employed for burning, in street lamps, in London.

Alcohol or spirit of wine, being cleaner than oil, is convenient for feeding a lamp that serves to heat a liquid in a small vessel; but the flame is blue, and therefore it is not suitable for giving light. In a spirit lamp, the surface of the spirit must be covered to exclude the air, for the spirit would catch fire if its surface were exposed.

Sulphuric ether is too easily inflamed, and too costly to be used for feeding lamps.

In a lamp for the purpose of giving light without a considerable quantity of heat, it is required that only a small portion of the oil shall be inflamed at once; therefore, by means of the wick, a small portion of oil, minutely divided so as to expose a large surface, is subjected to the action of the heat; the heat decomposes the oil, and the gas resulting from the decomposition is burned by the atmospheric air which surrounds the wick. In the gas lights, which have come into general use in manufactories and cities in Britain, the operations of producing the gas and inflaming it, which take place at one time in the wick of a lamp, arc performed separately. The gas is obtained from pitcoal, oil, or wood, but best from pit-coal or from oil, by heating these substances strongly in a retort; and, when extricated, is conveyed away in pipes to the place where it is to be inflamed. The capillary attraction of the filaments of the cotton which compose the wick of a lamp, raises up a small portion of oil into a situation where it may be exposed to the degree of heat necessary for producing flame.

In lamps of the most common structure, the wick should not be elevated too high above the surface of the oil; for, in that case, the capillary action by which the oil rises between the filaments of the cotton will not be able to raise it to so great a height. If the wick is too little elevated above the surface of the oil,’ there will not be a sufficient quantity of the oil converted into the gas, whose combustion constitutes the flame, and the flame will be too small.

Many lamps used by the Greeks and Romans have been found in the ruins of ancient towns. These ancient lamps are of pottery, painted and sculptured with various ornaments, and of bronze. The surface of the oil in the reservoir is nearly on a level with the lighted part of the wick, which emerges from a projecting beak at the side of the reservoir.

The lamp commonly used in rooms at Florence consists of a round reservoir, with four beaks projecting from four opposite points of its circumference; through the middle of the reservoir a vertical stalk passes; and on this stalk the lamp may be raised or slid down. The stalk is fixed in a foot that rests on the table, and the whole is made of brass.

A lamp, which affords a faint light, is made of a waxed wick, an inch long, passed through the centre of a thin round piece of cork, and of a piece of card placed above the cork. Some oil is placed on the surface of water in a glass tumbler, and the cork, with its wick, is laid upon the surface of the oil. This lamp, called a veilleuse, is commonly used in Paris for burning in bed-rooms during the night, as rush-lights are in London.

The lamp with a hollow cylindrical wick, which receives a current of air, both on the outside and the inside of the cylinder, is called in England an Argand lamp, from the name of one of the first makers. The wick in Argand’s lamp, as first constructed, was raised by a rack and pinion; but the method now employed to raise the wick consists in a spiral notch, which goes round outside of the interior tube. The inside of the ring to which the wick is attached has a tooth which fits into this notch.

At fig. 2, Plate CCCXXI., is a representation of the most usual form of the Argand lamp. A is a 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 admitted to [7:13:42]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 uncover the hole t, and the oil is poured in by the holer; when this is done, the hole is again covered by the sliding tube, and the reservoir A is replaced in F. W r hen 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 ċontains 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 surface of the oil in F is below the upper part of the hole; then a bubble of air ascends into A, and a 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 a considerable inconvenience attending oil reservoirs of the construction here mentioned. The hole t is closed by drawing up the sliding tube Q,, when the lamp is not burning, in order that the lamp may be inclined, without making the oil descend from the reservoir.

The cylindrical part, where the flame is produced, 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 immersed in oil. The wick is fixed to the wick tube, which is capable of being moved spirally; within the annular cavity is also the tube/, 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 receive the superfluous oil that drops down from the wick along the inner surface of the tube g. The air enters through the holes ο o, and passes up through the tube g to maintain the combustion in the interior of the circular flame. The air which goes to perform the combustion on the exterior part of the wick enters through the holes m, with which r 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: the contraction of the chimney was commonly employed in Paris before it was used in England.

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 w 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 h, connected with the wick-tubes w i. The wick-tube 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; τ n fits on the tube d ; r n is fitted to receive the glass chimney R G; a wire 5 is attached to the tube f and is bent over the edge of the tube / and descends along the outside of the tube d. The part n r, that supports the glass chimney, is connected, by four other wires, with the ring y, which surrounds the tube d, and is capable of being moved round. When n r is turned round, it carries round along with it the ring y, the wire s, and the tube ∕ and thereby operates the elevation and depression of the wick.

The glass chimney which rests on R N is wider at bottom, and then is contracted at R G, for the purpose of making the air rush upon the external part of the circular flame in a denser current.

In the most simple construction of 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 and .executed lamps of various forms, with the view of removing the inconvenience of the shadow of the reservoir, which is inherent in the common lamp with one lateral beak.

One of the contrivances for diminishing the bulk of the part in which the wick is immersed, and for obtaining a supply of oil, is the bird-cage fountain reservoir described above as being usually applied to Argand lamps. This kind of reservoir is described by Cardan, and a lamp fed by it is mentioned by several writers under the name of Cardan’s lamp.

Baptista Porta, in treating of oil reservoirs of the kind just now mentioned, proposes that, for large lamps with many wicks, the reservoir should be placed above and without the room, and should communicate with the lamp within by a pipe. In this way, the oil would not be liable to be pressed out too rapidly by the expansion of the air in the reservoir, occasioned by the heat of the room; and several methods have been contrived for the purpose of placing the luminous part of the wick on the upper end of a stalk, so that very little of the sphere of rays proceeding from the lighted wick may be intercepted by the opaque part of the lamp. The following are some of these methods:

A. lamp called the Amiens lamp, commonly used in Paris by the poorer classes, is in the form of a candle. The lighted part of the wick is at top. The lower part of this cylinder, which is of tin, has a valve opening upwards, and is moveable up and down in another cylinder, which has a valve opening upwards. This valve is plunged in the reservoir of oil; when the wick is in want of oil, the oil is pumped up by moving vertically the tin cylinder which contains the wick. Lamps of this kind are described in the Transactions of the Academy of Sciences for 1755, p. 139; and for 1760, p. 158.

A lamp for reading is made by Carcel of Paris, in which the oil is raised to the wick by means of a pump. The pump is moved by watch-work, composed of wheel and pinion, and a spring, which is wound up when the lamp is to be lighted.

In the twentieth volume of the Philosophical Transactions, St Clair, in a letter to Hooke, describes a lamp, in which the oil floats on water. A tube passes from the upper part of the vessel down to the water; and through this tube water is dropped, by means of which the surface of the oil is always maintained at the same level, whilst it is consumed by the flame in the wick.
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In the lamp constructed by Mr Keir of Kentish Town, the oil is raised to the wick, and sustained by a column of a solution of salt in water. This liquid being of a great> er specific gravity, a column of it counterbalances a longer column of oil. The solution of salt is made of such a specific gravity that it will support a column of oil four thirds of its own height. This is nearly the specific gravity of the heaviest saline solution that is known to exist in any great body of natural water, namely, in the Dead Sea; the weight of the waters of this sea, of distilled water, and of oil, being in the relative proportions of 120, 100, 92. To have an idea of this lamp, imagine a syphon with two upright branches, and the junction of the branches at the bottom. The shortest branch has a bulb at top. The longest branch has a bulb near its lower extremity. The shortest branch is filled with a solution of salt, whose upper surface is in the superior bulb. The longer branch contains the oil, and in its upper extremity the wick is placed. In the lower bulb the surface of the oil rests upon the surface of the solution of salt.

The bulbs serve as reservoirs, prolonging the action of the machine; by means of the bulbs and the greater specific gravity of the solution, it is effected, that the abstraction of a considerable quantity of oil by the combustion in the wick occasions but a small depression in the upper surface of the solution; the height of the sustaining column of solution will become shorter in proportion as the column of oil which it counterbalances is consumed; but this diminution of the height of the column of oil will be slow, and therefore the column of oil will for a considerable time be of sufficient length to reach the wick. Suppose an inverted syphon, of equal diameter throughout, the shorter leg of which contains a column of solution of salt, whose height is 75, and this counterbalances a column of oil, whose height is 100, in the longer leg; if now the column of oil in the longer leg be diminished in height by 10, the counterbalancing column of solution will diminish to 67∙5, being 7∙5 shorter than at first. But if the syphon, instead of being of equal diameter, has two dilatations or reservoirs, whose horizontal section is ten times the area of the tube of the syphon, one of the reservoirs being placed at the top of the short branch, so as to contain the upper surface of the solution of salt, and the other at the bottom of the long branch, so as to contain the surface where the oil rests upon the solution; then, if the same quantity of oil, as in the former example, is taken from the top of the longer leg of the syphon, the column of oil will only fall one tenth of what it did in the undilated syphon of equal diameter, and the solution of salt will diminish one tenth of what it did in the syphon of equal diameter.

The oil-reservoir and the wick remain stationary, and do not descend as the oil is consumed. This descent takes place in two lamps now to be mentioned, because in these two lamps the oil-reservoir swims in a liquid that acts as a counterpoise.

In the lamp contrived by the Chevalier Edelkrantz of Stockholm, the oil-reservoir floats in mercury, and the column of oil is maintained at the requisite height by the counterpoise of a column of mercury; in proportion as the oil is consumed, the oil-reservoir, and the wick which is connected with it, sink.

The general structure of this lamp may be understood by conceiving a flask, with a long narrow neck, and enlarged at the under part. The flask is heavy enough to swim, when it is placed in mercury, with its under part immersed. The bottom of the flask is open. The flask being placed in mercury, is made to float with its neck perpendicular. Oil is poured in at the neck till the flask is full. Then the surface of the mercury at the bottom of the flask and within the flask will be depressed by the weight of the column of oil that rests upon it; and the surface of the mercury on the outside of the bulb or lower part of the flask will stand higher than the surface of the mercury within the flask. The height which measures the difference of level of the two surfaces of mercury will be the height of a column of mercury of equal weight with the column of oil that is in the flask; and as mercury is about 14^θ times the weight of oil, the difference of level of the two surfaces of mercury will be ) + of the height of the oil in the flask. In proportion as oil is abstracted from the upper end of the tube by the combustion in the wick, the height of the column of oil is thereby diminished, and the two surfaces of mercury will come nearer to each other, the flask sinking a little in the mercury. As the area of the horizontal section of the lower part of the flask is much greater than the area of the section of the neck, and as the specific gravities of mercury and oil are very different, it follows, that, to restore the equilibrium after the abstraction of a column of oil from the neck, the surface of the mercury within the lower part of the flask will rise by a much shorter column.

In the lamp invented by Mr Barton, comptroller of his majesty’s mint, a solution of salt and water is used as a counterpoise to the oil. The combination consists of a light flask, open at the bottom, floating in a solution of salt, so that when oil is poured into the flask, the surface of the oil in the neck of the flask stands at a higher level than the surface of the saline solution in which the flask swims. The wick is at the upper end of the neck of the flask; and as the area of the horizontal section of the bulb or lower part of the flask ⅛ much greater, suppose twenty times greater, than the area of the section of the neck of the flask, it will happen, that when a column of oil an inch high is abstracted from the neck of the flask, the height of the rise of the surface of the solution in the bulb or lower part of the flask will be only one twentieth of an inch. This lamp is represented at fig. 3, Plate CCCXXI.

T is the oil-reservoir, from which the oil passes upwards to the wicks m , w, w. 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 the reservoir. The fluid B, in which the oil-reservoir is immersed, is a solution of salt in water. This liquid is contained in a vessel RMO, 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, h, 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 c, h and h, e; 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 e, h bears to the perpendicular height c, h. As the oil is consumed, the 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 solution of salt by the opening at I ; 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 [7:13:44]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.

An inconvenience affecting Barton’s lamp is, that the solution of salt, by the gradual evaporation of the watery part, becomes more dense, and capable of supporting a higher column of oil than it did at first. The lamp of Edelkrantz, which floats on mercury, is not liable to this inconvenience, because the mercury does not alter in density by evaporation. Both these floating lamps have the inconvenience, that the oil is made to run over at the wick by any accidental shock which depresses the floating part of the lamp.

Several lamps have been constructed, in which the oil is raised by the principle of the fountain of Hero of Alexandria, which is known as being employed to raise water in the mines of Chemnitz, in Hungary. In Hero’s writings, the application of this machine to raise oil to a lamp is described. Lamps of this construction were made some years ago in Paris by Girard de Marseille. Of this kind is the hydropneumatic lamp made by King, tin and japan manufacturer, of Snowhill, London. This lamp is formed externally like a column eighteen inches high and four inches in diameter; it is made to contain oil enough to last for five or six hours. An idea of its general principle may be formed by means of the diagram at fig. 5, Plate CCCXXI. in which there is a descending tube, with a bulb A at top. The upper part of this bulb is open. The tube, at its lower part, is curved upwards, and dilated into a second bulb B. The tube contains oil, the upper surface of which is in the upper bulb A, and its other surface is in the lower bulb B~ From the top of the lower bulb B a tube proceeds to the top of another bulb C, placed higher than the upper bulb A of the first tube. This third bulb C contains oil, and from the bottom of this third bulb the oil rises in a tube. At the upper end W of this tube the wick is placed. The whole machine is closed and air-tight, except at the openings of A and W; and at these openings the pressure of the atmosphere acts. Thus the column of oil contained in the first tube and bulbs A, B, presses, with its own weight and the weight of the atmosphere, on the confined air contained between the second bulb B and the third bulb C, and raises up a column of oil from that third bulb. The top of this column, so raised, is at a higher level than the top of the oil in the first tube, because the bottom of the column, which is raised, is at a higher level than the bottom of the column in the first tube. The whole machine is a syphon, in which a first column of oil of the perpendicular height AB supports a second column of oil CW, not of a greater height than the first column, but, by means of the column of air BC interposed between the two columns of oil, it is effected that the extremity W of the second column of oil is much higher than the upper surface A of the first column of oil. In the lamp constructed on this principle by King, there is a plug and valve which serve for introducing the oil, and other particular contrivances. When the oil is to be poured in, the lamp is inverted.

A lamp, of which the reservoir for the oil is in the form of a hollow ring, was contrived by Count Rumford, and is described by him in Nicholson’s Journal, vol. xiv. 1806, p. 23. The lamp is in the centre of the ring, with which it communicates by three straight tubes, in the direction of radii of the ring. The stoppers, which close the apertures by which the oil is poured into the ring, have a small hole, which allows the atmosphere to press on the surface of the oil in the ring, and thereby permits it to flow freely to the wick. This small hole may also be placed in some other part of the ring, and not in the stopper. The ring supports an hemispherical shade of roughened glass or of gauze. These glass shades are made rough, not by grinding, but by laying a coat of powdered glass on the smooth surface of the shade, and then exposing it to the heat of a furnace, so that the powdered glass becomes adherent, and produces a rough or frosted surface. This method of frosting glass is practised in some glass-houses situated in that district of Staffordshire called the Potteries. Lamps of this construction may be suspended from the ceiling, or placed on a stand, and are now frequently used in rooms and shops in London and Paris. They are called in London French lamps.

Hooke, in his treatise entitled Lampas, published in 1677, describes eight contrivances for supplying oil to a lamp equably, and as long as there remains any oil in the reservoir. This he effects by different methods of counterbalancing the oil. These inventions display Hooke’s ingenuity and great knowledge of mechanics, but require nice workmanship, and are not applicable to practical purposes. These counterpoises of Hooke also serve to form a vessel so that the whole liquid may be drawn from it in an equable stream, by tapping the vessel at the top, and to make the descent of the surface of a liquid and its discharge constant and equable in a clepsydra for showing the hour.

Porter’s automaton lamp, constructed in London in 1784, is something similar to some of Hooke’s contrivances for producing an equable supply of oil to the wick as long as there remains any oil in the reservoir. It does not require such delicacy of execution as Hooke’s counterpoised lamps. Porter’s lamp is a tin box, the vertical and longitudinal section of which is a rectangular parallelogram, elongated horizontally, of which call A, B the two upper angles, C, D the two lower. This parallelopipedal box is suspended on an axis near the upper surface of the box, at a place which may be denoted by X. The axis is nearer A than B; at A is the wick, and a tube going down to the bottom of the box, along the side of the box AC. When the box is full of oil, then the space XB, behind the axis, being full of oil, counterpoises the shorter space XA. AB, the long side of the box, is horizontal; and the line drawn from the axis of suspension down to the centre of gravity is perpendicular to AB. But when the surface of the oil falls below the axis, then the box turns on its axis, the side A falls, and B is elevated; A being heavier, by reason of the wick and wicktube, and the side AC assumes a lower position, in proportion as the oil is consumed; the line drawn from the axis down to the centre of gravity becoming more and more oblique to AB. The operation of this lamp depends upon the position of the axis X, and the weight of the wick-tube, which must be accurately proportioned, the one to the other, by trial.

LAMPS FOR LIGHT-HOUSES.

Light-houses are now generally lighted with Argand lamps, which have hollow cylindrical wicks placed before reflecting mirrors. Several of these lamps are fixed on a frame, and protected from the weather by glass windows. The lamps of light-houses are fed with oil, and in some places with pit-coal gas, as in a light-house near Trieste.

In many of the light-houses on the British coast, the frame on which the lamps are fixed is made to revolve by means of clock-work, so that to a spectator situated in the circle of which the light-house is the centre, the light appears at its brightest at the end of a stated period of time, which is generally one or two minutes. The revolving of the light enables seamen to distinguish the [7:13:45] light-house from the light of lime-kilns or other fires upon the coast. This distinction is of great importance; for shipwrecks have happened in consequence of mistaking the light of lime-kilns for the light of a light-house. The light is in some light-houses made of a red tinge, to distinguish it from some other light-house not far distant. The red colour of the light is produced by placing windows of red glass before the lamps. Red is the only colour that can be given to the light in this way. When stained glass of other colours is placed before the lamp, it is not found to produce a change in the colour of light seen at a distance; the blue or green colour of the glass becomes insensible when seen through a great body of air, which has itself a blue colour.

LAMPS FOR LIGHTING STREETS.

Till within the last six years, the street-lamps used in London and in other parts of Britain consisted almost uniformly of a deep inverted bell-shaped glass lantern, blown of one piece, and suspended by the edge in an iron ring, with a tin conical cover perforated to give issue to the smoke, and within the lantern a flat oil-vessel, with two or more wick-holders or beaks projecting from its circumference. Many districts of London are lighted with lamps of this form; other districts employ several kinds of street-lamps of a different form. The first of these new kinds was made under the direction of Lord Cochrane, and employed to light the streets in the parish of Saint Anne, Soho, London.

The lanterns which serve to protect the light from wind and weather in the new lamps in one district of London, are composed of four lateral panes and a bottom of glass, joined together by sheet iron, -so that the lantern is in form of a truncated pyramid, inverted like the lanterns of the street-lamps in Paris. In lanterns of this form some light is intercepted, and a shadow is thrown on the street by the metal that unites the panes. This defect does not occur in the lanterns of street-lamps most commonly used in England, and made of one piece of glass blown into the form of a spheroid. The spheroidal lanterns deflect the light more, because they are more unequal in thickness, but this is a smaller inconvenience; the lanterns blown of one piece of glass are more easily cleaned. Many of the lanterns for gas-lights are also made of panes in the above-mentioned form; some are cylindroids blown of one piece, with a hole in the bottom to admit air. In some of the new lamps in London which have lanterns of one piece of glass, the form of the lantern is nearly cylindrical; in others the lantern is not so deep as the lanterns of the old form. The new lamps have reflectors placed above the light, for the purpose of reflecting the light downwards on the foot pavement. These reflectors are of various forms in some of the lamps, the four plane surfaces of the inside of the pyramidal cover of the lantern are made bright, and serve to reflect the light downwards. In other lamps the ceiling of the lantern is a reflector in form, having a'small portion of a large curved surface, with a chimney in the middle to give issue to the smoke. Others have two, and sometimes three, concave conoidal reflectors, whose vertices meet over the light, the axes of two of the reflectors being parallel to the direction of the street; at the point where the reflectors meet there is a chimney, through which the smoke ascends. The reflectors require to be frequently wiped in order to keep them bright.

The oil-vessels of the new lamps in London are of various forms; the beak or part of the oil-vessel under the wick is made as narrow as possible; for as it is very near the flame, its shadow thrown on the street by the rays diverging from the flame is several feet in breadth. If the beak be an inch broad, and situate an inch under the flame, the shadow of the beak on the pavement under the lamp will be ten feet broad if the flame is situate ten feet above the pavement. In some of the new lamps the reflector placed above the light is made with its concavity so disposed at the edges that the reflected light is thrown upon that part of the pavement which is under the oil-holder. In Major Cochrane’s lamps the oil-vessel consists of a bird-cage fountain reservoir, which allows a supply of oil to come down to the wick when the surface of the oil in which the wick is placed has sunk to a certain point. The wick is double, consisting of two pieces of flat cotton web; between the wicks is a slit, through which a current of air ascends to the flame; on the outside of each wick is another slit; and these slits admit currents to the exterior surface of the wicks. Each time that the lamp is trimmed two pieces of wick are inserted, just sufficiently long to last the time that the lamp is required to burn. Naphtha distilled from pit-coal is burned in these lamps, and the light is brilliant like the light of coal-gas. But the gas-lights have the advantage of being unencumbered by the opaque substance of the oilvessel, which intercepts light, and casts a shadow on the street.

The street-lamps in London are fixed at the end of iron rods which project from the walls of the houses. The lamp is, over the middle of the foot pavement, ten feet from the ground. There is a row of lamps on each side of the street, the principal streets being fifty feet in width. In Paris, where many of the principal thoroughfare streets are not above twenty-five feet in breadth, the lamps are suspended over the middle of the street. A strong rope is made fast to the walls on each side of the street, and to this rope a smaller rope with the lamp is attached. The smaller rope passes'over-pullies, and its enc( comes down into an iron box, whereat is fixed on a hook. The iron box is unlocked, and’the'lamp is let down and lighted with a candle. The light is placed before a silver-plated reflector. In Vienna, the street-lamps are fixed on the upper end of a post. The lamp is taken out of the lantern by means of a pole, and lighted at the foot of the post. This saves the inconvenience which results to passengers from the mode of lighting lamps by a man with a ladder and torch, as practised in Britain. In most of the towns of Italy the streets are but sparingly lighted. The lamps are fixed at the end of iron rods which pro ject from the walls of the houses. In some of them the light is placed in the focus of a parabolic reflector, or at the meeting of the vertices of two concave conoidal divergent reflectors situated above the light. The French, when masters of Italy, made regulations to improve the lighting of the streets.

In England, whale-oil is used as the combustible material in the street-lamps; of late naphtha, obtained from the distillation of pit-coal, has been used in a district of London which is lighted with Major Cochrane’s lamps. This naphtha is a clear and colourless liquid, and is found to give a good light; it requires to be prepared with particular attention; that made at the gas-light work is said to be too easily inflammable. In Paris, rape-seed oil and poppy-seed oil arc used; these expressed oils are made in the north-eastern part of France, and in Flanders. In the south of Europe, olive-oil of inferior quality, and walnutoil, are used. Street-lamps lighted with the gas distilled from pit-coal were in 1821 employed in the principal streets of London, Edinburgh, Glasgow, Liverpool, Manchester, Birmingham, Sheffield, and other cities in Britain. The use of coal-gas for giving light had made very little progress in France in 1818, being scarcely employed even in Paris, and we believe not at all at Lyons, although pit-coal is abundant, and commonly used as fuel [7:13:46]there. In 1818, pit-coal gas was used for lighting a light-house on the Adriatic, in the dominions of the house of Austria near Trieste, the gas being obtained from the coal wrought in the adjacent country.

SAFETY LAMP.

This lamp was constructed for the purpose of giving light in mines where fire-damp prevails. In many of the collieries of Britain, Flanders, and other countries, firedamp, consisting of carburetted hydrogen, issues from different parts of the strata of coal when the coal is worked; and when the fire-damp is mixed with a certain proportion of atmospheric air, it explodes by the flame of the miner’s candle, burning the workmen severely, and often depriving them of life. Vegetable substances, in the slow decomposition which takes place in them, in the process of putrefaction, give out inflammable gas. This is seen when the leaves of plants fall into water and become putrid; inflammable gas then rises to the surface in bubbles, and is inflamed if a light be applied to the surface of the water. Vegetable matter gives out inflammable gas also in the rapid decomposition occasioned by fire. The flame of vegetable substances consists of the inflammable air resulting from their decomposition, and burning with the addition of the air of the atmosphere. Pit-coal consists of the remains of large quantities of vegetable substances; and the fire-damp of coal-mines may be considered as the produce of the putrefaction which the vegetable· matter has undergone, or of some decomposition that the coal is still undergoing. Sir Humphry Davy found that, on breaking some masses of coal under water, inflammable gas was given out. In some places blowers of fire-damp issue out at the surface of the earth. A quarter of a mile from Pietra Mala in the Apennines, on the road from Bologna to Florence, there is a blower of inflammable gas issuing from the ground, and proceeding from strata of schistus, and perhaps of coal. Sir Humphry Davy analysed this gas, and found it to be carburetted hydrogen, like the fire-damp of the coal mines. Another blower of the same kind exists on the side of a mountain near the shore of the Gulf of Adalia, in Lycia, on the south coast of Asia Minor. In mines wrought to obtain metals and salt, where there are no strata of vegetable matter like coal, it does not appear that the fire-damp occurs.

The merit of that very ingenious and most useful contrivance, the Safety Lamp, is wholly due to Sir Humphry Davy. After having made many experiments for the purpose of forming a lamp to give light in coal mines affected with fire-damp, without occasioning explosions, which frequently proved fatal to the miners, he found that wire-gauze, of which the apertures occupy more space than the cooling or radiating surface of the wire, so as to be permeable to air and light, offered a perfect barrier against explosion; because, although the gas was inflamed within the enclosures formed by the wire-gauze, yet the heat being communicated to the numerous surfaces of the wire, the gas on the outside of the wire enclosure was not inflamed. Wire-gauze is the best material for safety lamps, as it affords the greatest extent of radiating surface, and, by cooling, prevents all explosions that require a temperature higher than the temperature of the atmosphere. An example of the radiating and cooling action of wire is seen in the fire-guards of wire, which are hung upon the ribs of fire-plaćes in rooms to prevent sparks from being thrown into the room. These fire-guards, although they arc very near the fire, do not become hot. The apertures of the wire-gauze must be smaller, and the wire, which is the radiating and cooling surface, must be in greater quantity, in proportion as the gas in which the lamp is to be used is more inflammable. The fire-damp in coal-mines is in almost all cases carburetted hydrogen; and for excluding explosion from a lamp in that gas, it is found that the wire-gauze should contain 784 apertures in a square inch.

The wire-gauze should be of iron or copper. -Fine brass wire is improper, because it is too easily combustible by reason of the zinc it contains. The iron wire should not be tinned, tin being too easily combustible. The body of the lamp should be of copper riveted together, or of massy cast brass or cast iron. The screws should fit tight; no aperture, however small, should be suffered to exist in the body of the lamp; and the trimming wire should move through a long tight tube.

The safety lamp is represented in Plate CCCXXI. fig. 4. A is the cistern containing the oil; B the brass rim to which the bottom of the wire-gauze cylinder is fastened by a screw, to prevent it from being separated from the lamp; C is the safe feeder through which oil is poured into the lamp; E the safe trimmer, a wire which passes through a safe tube, for the purpose of raising and trimming the wick; F the wire-gauze cylinder. The longitudinal suture where the two edges of the piece of wire-gauze that forms the cylinder meet, must be well doubled and fastened with wire. If the cylinder is of twilled wire-gauze, the wire should be of iron or copper, at least of the thickness of 1/40th of an inch; if of plain wire-gauze, the diameter should not be less than 1/60th of an inch. The number of apertures in a square inch should not be less than 786. The wire-gauze cylinder F is closed at top by a circular piece of wire-gauze, and above this is placed a second top, G, which fits on the cylinder like a cap. In the figure the circular wire-gauze top of the wire-gauze cylinder is seen at G through the wire-gauze of the cap. The circular top of this wire-gauze cap is 3/4ths of an inch above the top of the wire-gauze cylinder F. II are thick wires surrounding the wire-gauze cylinder, to prevent it from being bent by external force. K is a ring to hang up the lamp, or to hold it by. The most convenient size for the safety lamp is a span, that is, from 8 to 10 inches high, the wire-gauze cylinder being 2 to 2⅜ inches in diameter.

The wire-gauze, when choked with coal-dust, requires to be cleaned by means of a brush, in order to transmit the light.

In figure 4, a lens of glass, L, is placed before the light; sometimes a piece of tin is placed within the cylinder to act as a reflector.

The light of the safety lamp, without a reflector, was found to be nearly equal to the light of a common miner’s candle.

Flame produced by the combustion of explosive gases may be extinguished by colder metal. The temperature of metal, even when heated to a white heat, is less than the temperature of flame, and therefore red-hot wire-gauze in sufficient quantity, and of the proper degree of fineness, will abstract sufficient heat from the flame of carburetted hydrogen or fire-damp to extinguish that flame.

Flame, in all cases, is considered to be the combustion of an explosive mixture of inflammable gas and air. If a piece of wire-gauze is held over the flame of a lamp, it prevents the flame from passing. The air that passes through is very hot, and is in the state of an explosive mixture, for it will be inflamed if a lighted taper be presented to it. But it is cooled below the exploding point, by passing through the wires, even if the wires are red hot; it is also cooled by being mixed with a considerable quantity of air comparatively cold. The temperature of visible flame is very high, as is seen by the fusion of a small filament of that difficultly fusible metal platinum, which happens when the filament is held in the flame of a candle. A considerable mass of heated metal is required[7:13:47] to inflame fire-damp. An iron wire of ⅛th of an inch in diameter, and 8 inches long, red hot, when held perpendicularly in a stream of fire-damp, did not inflame it. But wire of the same size, when six inches of it were red hot, and when it was held perpendicularly in a bottle containing an explosive mixture, so that successive portions of the gas were heated by the wire, produced an explosion.

The action of the safety lamp may be exhibited in the chemist’s laboratory, by pouring some ether into the bottom of a large jar; the vapour of the ether mixing with the air, produces an explosive atmosphere. When the safety lamp is lighted and placed in the jar, the explosive mixture from the ether will burn within the wire-gauze lamp, without inflaming the gas that is without it.

The workman who has only a single gauze lamp, and finds the temperature of the wire increasing rapidly by the fire-damp from a blower, can easily diminish the heat by standing between the current and the lamp, that is to say, to the windward of the lamp, or by sheltering the lamp from the current by interposing his clothes; or, by bringing the lamp nearer the orifice from which the firedamp issues, he may extinguish it. There never can be any occasion for the workmen to place the lamp in the exact place, when two currents, one of common atmospheric air, and the other of fire-damp, meet each other.

When the fire-damp is inflamed in the w ire-gauze lamp, coal-dust thrown into the gauze cylinder burns with strong flashes; but the explosion is not communicated to the external fire-damp by this means.

Phosphorus, sulphur, pyrites, or gunpowder, would produce explosion by being applied to the outside of the wire-gauze cylinder; and sulphur, to produce this effect, must be applied in large quantities, and blown upon by a current of atmospheric air. But there is little danger of these substances being accidentally applied to the safety lamp in mines.

When a wire-gauze lamp is made to burn in a very explosive atmosphere at rest, the heat of the wire-gauze, when the fire-damp is burning within the lamp, soon arrives at its maximum, and then diminishes. The coally matter also, from the decomposition of the oil, chokes the upper apertures of the wire-gauze, and thus gradually diminishes the heat, by diminishing the quantity of gas consumed. Wire-gauze lamps which had been used by workmen for several months, and which had been often red hot in explosive atmospheres, were nevertheless still unimpaired and perfect.

Where the lamp is placed in a current of explosive gas, a greater heat is produced; and in this case the radiating or cooling surfaces should be increased. Twilled gauze or a double or triple fold of wire gauze on one side of the lamp, or a skreen of metal between the lamp and the current, or a semi-cylinder of glass or mica within, answers the object of preventing the heat from rising to redness.

If the heat of the iron wire-gauze rose to that of a strong welding heat, a circumstance which never could happen in a colliery, then the iron wire would burn, and the lamp would be no longer safe.

From a mine of Lord Durham’s there is a violent blower of fire-damp conveyed to the surface, upon which the following experiment was made: A brass pipe was fixed upon the blower-tube, so as to make the whole stream of fire-damp pass through an aperture of less than half an inch in diameter. The fire-damp, when inflamed, issued from this with great violence and noise, forming a flame of five feet long. This blow-pipe was exposed at right angles to a strong wind. The double gauze lamps soon became red hot at the point of action of the two currents; but the wire did not burn, nor did it communicate explosion. The single gauze lamp did not communicate explosion as long as it was red hot, and slowly moved through the currents; but when it was fixed at the point of the most intense combustion, it reached a welding heat; the iron wire began to burn with sparks, and the explosion then passed.

In other experiments on this blower of fire-damp, single wire-gauze lamps, with slips of tin-plate on the outside or in the inside, to prevent the free passage of the current, and double lamps, were exposed to all the circumstances of the blast; but the heat of the wire never approached near the point at which iron wire burns, and the explosion was not communicated. The flame of the fire-damp flickered and roared in the lamps, but did not escape without the limits of the wire-gauze.

The sparks from a flint and steel mill, a machine which sometimes has been used to give light in mines affected with fire-damp, would most probably inflame such a current as the blower above mentioned; because the sparks elicited from steel by the collision of flint, are small portions of the steel in a burning state, as may be seen by collecting these sparks on a sheet of paper, and viewing them with a microscope.

The lamp without flame, which is sold as an object of amusement and curiosity, consists of a fine wire of platinum of the 1/100th an inch in diameter, coiled into a spiral, and placed round the wick of a lamp fed with the spirit of wine, and a little above the wick; when the flame of the lamp is blown out, the heat which the wire has acquired is sufficient to keep up the slow combustion of the vapour of the spirit of wine, and this combustion continues to keep the platinum in an ignited state. The principle of this lamp without flame may be usefully applied to the safety lamp. By hanging some coils of fine wire of platinum above the wick of the lamp, it is believed that the coal-miner will be supplied with light in mixtures of fire-damp, which, from the small proportion of atmospheric air, are no longer explosive; and should the flame of the lamp be extinguished by the quantity of fire-damp, the glow of the incandescent platinum will continue to give light, and the incandescence will cease when the air becomes unrespirable. Sir Humphry Davy found, that a spiral wire of platinum of the 1/60th or 1/70th of an inch in diameter, suspended within the safety lamp, yields light in a mixture of fire-damp with atmospheric air, in which the atmospheric air is in so small a proportion that the mixture is not explosive. In this situation, the heat is not sufficiently great to produce combustion with flame, and combustion without flame takes place. The platinum wire, heated by the flame of the lamp, retains its heat after the flame is extinguished, and this heat is sufficient to occasion a slow combustion or combination of the elements of the fire-damp with the oxygen of the atmospheric air: this slow combustion produces sufficient heat to keep the platinum in a state of ignition. Platinum and palladium are the only metals found to produce this effect, because these two metals are of a slow conducting power and capacity for heat. This phenomenon takes place in mixtures of gas where there is common air enough to support the respiration of human beings.

At Wallsend, and other extensive collieries near Newcastle, in Northumberland, the following regulations respecting the safety lamps are observed: A steady man is employed to take charge of the lamps, and he is responsible for keeping them in good order. A chamber is allotted him, in which he keeps oils, cotton, and spare lamps; the chamber is in a secure part of the mine, as near the workings as possible. The brass collar of the wire-gauze cylinder is secured to the bottom of the lamp by a lock, which can be opened only by the lamp-keeper; so that the workmen cannot separate the wire-gauze cylinder from the bottom of the lamp. After finishing their [7:13:48]day’s work, the colliers bring the safety lamps to the lamp-keeper’s cabin. The lamp-keeper unlocks the lamps, keeps the bottom, and allows the colliers to take the wire-gauze cylinders home for the purpose of cleaning them. When the colliers return to their work next day, the lamp-keeper, having replenished the lamps with oil and cotton, lights the wicks, screws on the gauze cylinders, and examines them carefully; if any defect appears in the gauze, the lamp is set aside to be repaired. The lamp-keeper’s business, during the day, is to walk leisurely through amongst the workmen, carrying some spare lamps with him to replace those which happen to be extinguished.