LAMP. Technically a lamp is an apparatus in which to burn fluid combustible substances. Lamps are mostly intended for yielding light; but there are also special forms the purpose of which is to afford highly concentrated heat in a convenient and portable form. The substances used in lamps for lighting are of two classes(1) fixed oils, and (2) fluid hydrocarbons obtained from the distillation of bituminous shales, &c. (paraffin oil), petroleum, and essential oils. The latter class may be distinguished as mineral oils. Till very recently fixed oils were almost exclusively used for lamps ; but since the introduction of the cheaper and more convenient mineral oils, in the second half of the 19th century, the use of fixed oils has steadily decreased in all parts of the world.
There is scarcely any fixed or fatty oil which has not been used, more or less, for burning. Many oils are so used in the districts which produce them, although they hardly enter into ordinary commerce under the name of burning oils. The so-called fish oils (sperm, whale, and seal) were, in recent times, principal burning oils, and to a limited extent are still so employed. Of the vegetable oils of commerce, colza oil is the most extensively used as an illuminant, and after it come other rape oils, poppy oil, the lower qualities of olive oil, sesamum or gingelly oil, candle-nut oil, and ground-nut oil, all of which, however, are local or restricted in consumption. The suitability of fixed oils for burning purposes depends on their purity or freedom from foreign matters, and on their limpidity, or, what is in effect the same thing, the temperature at which they solidify. Thus cocoa-nnt fat is consumed in ordinary lamps in tropical regions, although in temperate latitudes it is a permanent solid. In the combustion of a fixed oil in lamps, the oil undergoes destructive distillation, and at the burning point is resolved into a gaseous mixture. The comparative viscosity of all fixed oils renders it neces-sary to adopt some device supplementary to the capillary action of the wick for maintaining at the level of the burner a supply of oil sufficient to support uniform com-bustion. Again, the lubricant properties of fixed oils make it practicable to adopt various mechanical devices to regulate the supply of fuel to the burner, and otherwise control illumination.
The mineral oils, on the other hand, are, as sold, mixtures of various volatile hydrocarbons which give off inflammable vapours at comparatively low temperatures, and in consumption in lamps they come to the burning point in the condition of vapour. With highly volatile oils, and the use of imperfectly fitted lamps, though not with proper oil and fittings, there is some danger of explo-sion ; there is also a risk that with imperfect combustion deleterious gases may be diffused through an apartment. Mineral oils possess such a high degree of limpidity that the suction of the wick alone is generally sufficient to bring the necessary supply of fuel to the burner.
The qualities of a lamp are judged of by the brilliance, steadiness, and uniformity of light it yields in proportion to the quantity of oil it consumes; by the convenient position of the light in relation to the equal illumination of the space it has to light; by the form, portability, and convenience of the lamp itself ; and by the simplicity and economy of its construction, regard being had to efficiency. The chief points to consider in connexion with the structure of lamps are (1) the means of supplying oil to the burner and of regulating that supply, (2) the form and arrangement of the wick or medium over which the flame is supported, (3) the regulation and control of the currents of air in the lamp which support combustion, and (4) the position of the oil reservoir in relation to the dissemination of the light and the stability of the lamp itself.
The simple form which was used down to the end of the 18th century, and which as a "cruisie" continued in com-mon use in Scotland till the middle of this century, illustrates the most elementary and most imperfect arrangement of a lamp. Here, as in the lamps of antiquity, the oil vessel lies immediately behind the burning point of the wick, with which the oil is about level when the reservoir is full. The wick is a round soft cord or fibrous mass. Such a lamp has no merit but simplicity. The light is thrown only forward and to the sides, the back being entirely in shadow. The wick, being a round solid mass, takes up oil equally at the centre and circumference ; but to the outer edges of the flame only is there any access of air ; conse-quently combustion in the centre is imperfect, resulting in a smoky unsteady flame, and a discharge into the atmosphere of the acrid products of destructive distillation. Further, as the level of the oil sinks in the reservoir, the wick has to feed the flame from a greater distance by mere capillary force, and, the supply thus diminishing, the light decreases in proportion.
Since the time when inventors first began to better the primitive lamp, just one hundred years ago, the improve-ments in lamp construction have been enormous ; the forms and modifications of invention bearing on lamps have been innumerable, and many excellent devices which did good service have been superseded by others simpler and more efficient. Notice can here be taken only of such inventions as developed new principles and features of originality.
The first improvement was in wicks and burners. In 1783 Leger of Paris devised a flat band or ribbon wick and buruar, which produced a broad thin flame with no core, so that all parts of the oil supply were brought into intimate contact with the air, and perfect combustion and a steady flame were secured. The deficiencies of the flat wick flame were that the light was comparatively thin and impoverished, and that the parts of a room facing the thin ends of the flame were badly illuminated. To some extent these evils were overcome by the adoption of a curved form of burner, which in the end led up to the burner invented by Ami Argand of Paris, and patented in England in 1784. In its simplest form the Argand burner consists of two concentric tubes or cylinders, between which the tubular wick is contained. The inner tube is open throughout, and to it a current of air passes from below, and, being carried upwards by the draught of the flame, atmospheric oxygen for combustion is supplied as well to the inner circumference as to the outer side of the flame, whence the name " double current burner " which it frequently receives. An adequate and controllable flow of air to the interior of the Argand burner having been secured, it remained to devise some means by which the current supplied to the outer circumference of the flame could be strengthened and regulated. This Argand secured by means of a chimney, which was made at first of sheet iron and suspended over the flame; but that device was quickly abandoned in favour of a glass chimney which rested on a perforated gallery placed a little below the level of the burner. Sub-sequent experience suggested the formation of a shoulder or constriction on the chimney at a point a little above the level of the flame, whereby the air current is directed inward against the external surface of the flame, thus materially improving the combustion. Argand's original burner is the parent form of innumerable modifications all more or less complex in their adaptations.
A typical example of the burner and chimney is represented in fig. 1, in which the burner is composed of three tubes, cl, /, 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 H, 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 o, o, and passes up through the tube g to maintain the com-bustion 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 rra is perforated. "When j the air in the chimney is rarefied by [ the heat of the flame, the surround-ing heavier air, entering the lower part of the chimney, passes upward with a rapid current, to restore the equilibrium. RG is the cylindrical glass chimney with a shoulder or constriction at R, G. The oil flows from a side reservoir, and occupies the cavity between the tubes g and d. The part hi is a short tube, which receives the circular wick, and slides spirally on the tube g, by means of a pin working in the hollow spiral groove on the exterior surface of g. The wick-tube has also a catch, which works in a perpendicular slit in the tube /; and, by turning the tube /, the wick-tube will be raised or lowered, for which purpose a ring, or gallery, rn, fits on the tube d, and re-ceives the glass chimney RG ; a wire S is attached to the tube /, and, bending over, descends along the outside of d. The part rn, that supports the glass chimney, is connected by four other wires with the ring q, which surrounds the tube d, and can be moved round. When rn is turned round, it carries with it the ring q, the wire S, and the tube/, and thereby produces elevation or de-pression of the wick.
A device in the form of a small metallic disk or button, known as the Liverpool button from having been first adopted in the so-called Liverpool lamp, effects for the current of air passing up the interior of the Argand burner the same object as the constriction of the chimney RG secures in the case of the external tube. The button fixed on the end of a wire is placed right above the burner tube g, and throws out equally all round against the flame the current of air which passes up through g. The result of these expedients, when properly applied, is the production of an exceedingly solid brilliant white light, absolutely smokeless, this showing that the combustion of the oil is perfectly accomplished.
The means by which a uniformly regulated supply of oil is brought to the burner varies of course with the position of the oil reservoir. In some lamps, not now in use, by ring-formed reser-voirs and other expedients, the whole of the oil was kept as nearly as possible at the level of the burner. In what are termed fountain, reading, or study lamps, the principal reservoir is above the burner level, and various means are adopted for maintaining a supply from them at the level of the burner. But the most convenient position for the oil reservoir in lamps for general use is directly under the burner, and in this case the stand of the lamp itself is utilized as the oil vessel. In the case of fixed oils it is necessary with such lamps to introduce some appliance for forcing a supply of oil to the burner, and very many methods of effecting this have been de-vised, most of which were ultimately superseded by the moderator lamp. The Carcel or pump lamp, invented by Carcel in 1800, is still to some extent used in France. It consisted of a double piston or pump, forcing the oil through a tube to the burner, worked by ingenious clockwork arranged to go a certain number of hours.
An example of a form of reading lamp still in general use is seen in section in fig. 2. The lamp is mounted on a standard on which it can be raised or lowered at will, and fixed by a thumb screw. The oil reservoir is in two parts, the upper ac being an inverted flask which fits into bb, from which the burner is directly fed through the tube d; h is an overflow cup for any oil that escapes at the burner, and it is pierced with air-holes for admitting the current of air to the centre tube of the Argand burner. The lamp is filled with oil by withdrawing the flask ac, filling it, and inverting it into its place. The under reservoir bb fills from it to the burner level ee, on a line with the mouth of ac. So soon as that level falls below the mouth of ac, a bubble of air gets access to the upper reservoir, and oil again fills up bb to the level ee, and so on it goes as long as Fl°- 2.Section of Reading Lamp, combustion continues and the supply of oil in ac endures. The principle is susceptible of numerous modifications.
The moderator lamp (fig. 3), invented by M. Franehot about 1836, from the simplicity and efficiency of its arrangements rapidly super-seded almost all other forms of mechanical lamp. The two essential features of the moderator lamp are (1) the strong spiral spring which, acting on a piston within the cylindrical reservoir of the lamp, serves to propel the oil to the burner, and (2) the ascending tube C through which the oil passes upwards to the burner. The latter consist of two sections, the lower fixed to and passing through the piston A into the oil reservoir, and the upper attached to the burner. The lower or piston section moves within the upper, which forms a sheath enclosing nearly its whole length when the spring is fully wound up. Down the centre of the upper tube passes a wire, "the moderator," G, and it is by this wire that the supply of oil to the burner is regulated. The spring exerts its greatest force on the oil in the reservoir when it is fully wound up, and in proportion as it expands and descends its power decreases. But when the apparatus is wound up the wire passing down the upper tube extends through-out the whole length of the lower and narrower piston tube, ob-structing to a certain extent the free flow of the oil. In proportion as the spring uncoils, the length of the wire within the lower tube is decreased ; the upward flow of oil is facilitated in the same ratio as the force urging it upwards is weakened. In all mechani-cal lamps the flow is in excess of the consuming capacity of the burner, and in the moderator the surplus oil, flowing over the wick, falls back into the reservoir above the piston, whence along with new supply oil it descends into the lower side by means of leather valves a, a. B represents the rack which, with the pinion D, winds up the spiral spring hard against E when the lamp is prepared for use. The moderator wire is seen separately in GG; and FGC illustrates the arrangement of the sheath-ing tubes, in the upper section of which the mo-derator is fixed.
Lamps for Mineral Oils. At an early period numerous at-tempts were made to utilize the highly in-flammable volatile hy-drocarbons and alco-hols, which from their cheapness and abund-ance offered some hope of competing with the fixed oils then in uni-versal use for illumi-nating purposes. These lamps had little success, and no small danger accompanied their li-mited use. The Vesta
Section of Moderator Lamp.
lamp of Young, introduced in 1834 for burning spirit of turpentine under the name of camphine, procured a smoke-less flame by means of the Argand burner, constricted chimney, and Liverpool button, with the access of abundant air. It was not, however, till the introduction of paraffin oils and petroleum that mineral oil lamps became of great importance. Lamp makers had not to direct their attention to mechanical arrangements, for mineral oils rise abundantly by capillarity alone; the problem was to produce a suffi-ciently powerful current of air to ensure complete and smokeless combustion of these richly carbonaceous com-pounds, and, in view of the highly volatile nature of the liquids dealt with, to prevent their exposure to the air, and more particularly to prevent the heating of the oil reservoir which would generate explosive mixtures, or vapours of dangerous tension.
Mineral oil lamps, like those for fixed oils, are constructed with both circular or tubular and flat-wick burners. In the case of the latter a cone or brass cap is placed over the burner, having a slit or opening a little longer and wider than the wick-holder itself. This cone serves to direct the whole current of air which enters below against the surface of the flame, and mingling with the vapour of the oil pro-duces perfect combustion, with a white flame which rises over the slit in the cone. The cool air current entering under the cone is also beneficially utilized in preventing the undue heating of the oil reservoir and the metallic wick-holder which passes down into it.
These flat wick lamps are simple in construction, cheap, and, so far as they go, economical light producers, but their flame is thin, and it is not practicable to compensate for the thinness by increased breadth of wick, because in such a case the edges of the light come so near the chimney that at these points the glass becomes rapidly heated, causing unequal expansion and destruction of the chimney. In 1865 Messrs James & Joseph Hinks of Birmingham secured a patent for improvements in the burners of mineral oil lamps, "whereby two or more flat flames or one circular or nearly circular flame may be produced by the use of two or more single flat wicks." Under this patent was manufactured their well-known duplex lamp, which has gone far to supersede all other forms. An improved form of their lamp is shown in fig. 4, in which a portion of the cone B is removed to show the two parallel flat wicks A, A, which have each a separate slit or opening in the cone. C is the coincident winder for raising or lowering the wicks in the tubes, by which the wicks can be moved separately or simul-taneously as desired. D is a lever for raising the extinguishers E, whereby not only is the light instantly extinguished, but the wicks are also covered and protected from dirt, while all evaporation by the wick-holder is prevented. Messrs Hinks & Son have further devised an automatic lighting attachment which obviates the ne-cessity of raising the glass chimney for lighting the lamp.
FIG. 4.Duplex Burner. FIG. 5.Conical Burner.
Messrs Hinks claimed in their 1865 patent the use of " two or more flat flames," and since that period numerous burners have been produced in foreign countries in which more than two flat wicks are used. The crown burner of Briinner in Vienna contains no less than six flat wicks. There are triplex burners, too, in which the wicks are arranged as a triangle ; a most valuable lamp of this con-struction is the '' Hesperus of Messrs Jones & Willis of Bir-mingham. Another form, the triplexieon, has three burners so closely placed together that the flames coalesce into a solid flame about half an inch in thickness. Further, there are star-shaped and cruciform burners, and others of little practical value.
The circular or tubular burners for mineral oils have been much simplified from the forms necessary in the case of colza, &c. A tubular wick is no longer required ; a simple flat wick of a size that will allow its edges exactly to meet round the upper edge of the burner ring is used instead. In the form shown in fig. 5 the wick-holder and burner consists of a hollow truncated cone, with a vertical conical section removed from its side. The flat wick passes up through this cone, its edges meeting and forming in effect a circular wick at the top, while the central current of air gets ready access to the tube by the conical opening formed in its side, and the outer current passes up within the chimney walls as usual. This form also is easily susceptible of numerous modifications. (J. PA.)
Ancient Lamps.Though Athenseus states (xv. 700) that the lamp (______) was not an ancient invention in Greece, it had come into general use there for domestic purposes by the 4th century B.C., and no doubt had long before been employed for temples or other places where a permanent light was required in room of the torch of Homeric times. Herodotus (ii. 62) sees nothing strange in the "festival of lamps," Lychnokaie, which was held at Sais in Egypt, except in the vast number of them. Each was filled with oil so as to burn the whole night. Again he speaks of evening as the time of lamps (______, vii. 215). Still, the scarcity of lamps in a style anything like that of an early period, compared with the immense number of them from the late Greek and Roman age, seems to justify the remark of Athenaeus. The commonest sort of domestic lamps were of terra-cotta and of the shape seen in figs. 6 and 7, with a spout or nozzle (______) in which the wick (______) burned, a round hole on the top to pour in oil by, and a handle to without noz-zles. Decora-tion was con-fined to the front of the handle, or more commonly to the circular space on the top of the lamp, and it consisted almost always of a design in relief, taken from mythology or legend, from objects of daily life or scenes such as displays of gladiators or chariot races, from animals and the chase. A lamp in the British Museum has a view of the interior of a Roman circus with spectators looking on at a chariot race. In other cases the lamp is made altogether of a fantastic shape, as in the form of an animal, a bull's head, or a human foot. Naturally colour was excluded from the ornamentation except in the form of a red or black glaze, which would resist the heat. The typical form of hand lamp (figs. 6, 7) is a combination of the flatness necessary for carrying steady and remaining steady when set down, with the roundness evolved from the working in clay and characteristic of vessels in that material. In the bronze lamps this same type is retained, though the roundness was less in keeping with metal. Fanciful shapes are equally common in bronze. The standard form of handle consists of a ring for the fore finger and above it a kind of palmette for the thumb to press on to keep the lamp steady. Instead of the palmette is some-times a crescent, no doubt in allusion to the moon. It would only be with bronze lamps that the cover protecting the flame from the wind could be used, as was the case out of doors in Athens. Such a lamp was in fact a lantern. Apparently it was to the lantern that the Greek word lampas, a torch, was first transferred, probably from a custom of having guards to protect the torches also. Afterwards it came to be employed for the lamp itself (_____, lucerna). When Juvenal (Sat, iii. 277) speaks of the aenea lampas, he may mean a torch with a bronze handle, but more probably either a lamp or a lantern. Lamps used for suspension were mostly of bronze, and in such cases the decoration was necessarily on the under part, so as to be seen from below. Of this the best example is the lamp at Cortona, found there in 1840 (engraved, Mowumenti d. Inst. Arch., iii. pis. 41, 42, and in Dennis, Cities and Cemeteries of Etruria, 2d ed., ii. p. 403).
It is set round with sixteen nozzles ornamented alter-nately with a siren and a satyr playing on a double flute. Between each pair of nozzles is a head of a river god, and on the bottom of the lamp is a large mask of Medusa, surrounded by bands of animals. These designs are in relief, and the workmanship, which appears to belong to the beginning of the 5th century B.C., justifies the esteem in which Etruscan lamps were held in antiquity (Athenams, xv. 700). Of a later but still excellent style is a bronze lamp in the British Museum found in the baths of Julian in Paris (figs. 8, 9, 10). The chain is attached by means of two dolphins very artistically combined. Under the nozzles are heads of Pan (fig. 8) ; and from the sides
FIG. 9.Bronze Lamp in British Museum.
project the foreparts of lions (fig. 10). To what extent lamps may have been used in temples is unknown. Pro-bably the Erechtheum on the acropolis of Athens was an exception in having a gold one kept burning day and night, just as this lamp itself must have been an exception in its artistic merits. It was the work of the sculptor Calli-machus, and was made ap-parently for the newly rebuilt temple a little before 400 B.C. When once filled with oil and lit it burned con-tinuously for a whole year. The wick was of a fine flax called Carpasian (now under-stood to have been a kind of cotton), which proved to be the least combustible of all flax (Pausanias, i. 26, 7). Above the lamp a palm tree of bronze rose to the roof for the purpose of carrying off the fumes. But how this was managed it is not easy to determine unless the palm be supposed to have been inverted and to have hung above the lamp spread out like a reflector, for which purpose the polished bronze would have served fairly well. The stem if left hollow would collect the fumes and carry them out through the roof. This lamp was refilled on exactly the same day each year, so that there seems to have been an idea of measuring time by it, such as may also have been the case in regard to the lamp stand (Aiiyvetoi/) capable of holding as many lamps as there were days of the year, which Dionysius the Sicilian tyrant placed in the Prytaneum of Tarentum. At Pharas in Achaia there was in the market-place an oracular statue of Hermes with a marble altar before it to which bronze lamps were attached by means of lead. Whoever desired to consult the statue went there in the evening and first filled the lamps and lit them, placing also a bronze coin on the altar. A similar custom prevailed at the oracle of Apis in Egypt, Pausanias adds (vii. 22, 2). At Argos he speaks of a chasm into which it was a local custom continued to his time to let down burning lamps, with some reference to the goddess of the lower world, Persephone (ii. 22, 4). At Cnidus a large number of terra-cotta lamps were found crowded in one place a little distance below the surface, and it was conjectured that there must have been there some statue or altar at which it had been a custom to leave lamps burning at night (Newton, Discoveries at Halicarnassus, &c, ii. p. 394). These lamps are of terra-cotta, but with little ornamentation, and so like each other in workmanship that they must all have come from one pottery, and may have been all brought to the spot where they were found on one occasion, probably the funeral of a person with many friends, or the celebration of a festival in his honour, such as the parentalia among the Romans, to maintain which it was a common custom to bequeath property. For example, a marble slab in the British Museum has a Latin inscription describing the property which had been left to provide among other things that a lighted lamp with incense on it should be placed at the tomb of the deceased on the kalends, nones, and ides of each month (Mus. Marbles, v., pi. 8, fig. 2). For birthday presents terra- cotta lamps appear to have been frequently employed, the device generally being that of two figures of victory holding between them a disk inscribed with a good wish for the new year:ANNV NOV FAVSTV FELIX. This is the in- scription on a lamp in the British Museum, which besides the victories has among other symbols a disk with the head of Janus. As the torch gave way to the lamp in fact, so also it gave way in mythology. In the earlier myths, as in that of Demeter, it is a torch with which she goes forth to search for her daughter, but in the late myth of Cupid and Psyche it is an oil lamp which Psyche carries, and from which to her grief a drop of hot oil falls on Cupid and awakes him. Terra-cotta lamps have very frequently the name of the maker stamped on the foot. Clay moulds from which the lamps were made exist in considerable numbers. (A. S. M.)
The first part of the above article was written by James Paton.
The second part of the above article (on ancient lamps) was written by A. S. Murray.