ELECTRICAL EXHIBITION AT PHILADELPHIA. 



305 



nra in this lamp, were exhibited. This min- 

 eral is found in large quantities in Henderson 

 Co., N. C., where it was first brought to light, 

 and then thought to be worthless. Since it has 

 exhibited the remarkable property of being in- 

 fusible, it can be used instead of the more ex- 

 pensive metal, iridium. 



The enormous lamp on the top of the tower 

 had an arc that leaped three quarters of an 

 inch, the carbon-rods bein? also three quarters 

 of an inch in diameter. Most of the arc-lamps 

 in and around the building were surrounded by 

 opal or ground-glass globes, for the purpose of 

 diffusing the light. The arc-lamps that illu- 

 minated the fountain were so arranged that 

 sheets of colored glass could be interposed, in 

 this way coloring the fountain and producing 

 many beautiful effects. The principal lighting 

 within the building was also done by arc-lamps, 

 they being strung along each of the high arches 

 supporting the roof. The illumination through- 

 out the building was as brilliant as sunlight. 



Incandescent Lamps. The little incandescent 

 lamps, 5,600 in number, which were strung 

 everywhere, were manufactured by S\van, Max- 

 im, Gerard, Edison, Weston, and Bernstein. 

 Edison showed about 1,000, arranged spirally 

 on a cylinder twenty feet high, some surround- 

 ed by white and others by colored bulbs, mak- 

 ing a most beautiful effect. To the casual 

 glance they are all much alike, having in com- 

 mon a filament of carbon bent in various shapes 

 and clamped to leading wires, which are of 

 platinum, as they pass through the glass bulb 

 Hut incloses the filament, in which a high 

 vacuum is produced. The point in which the 

 incandescent lamps differ one from another is 

 in the material composing the filament, and in 

 its shape. This little filament has many ene- 

 mies, the most formidable of which is called 

 molecular carriage; that is, the carbon-parti- 

 cles are carried from the positive side of the 

 loop to the negative, causing the filament t j 

 waste gradually until it breaks, and the lamp 

 is destroyed. The various materials used in 

 the different incandescent lamps are valuable 

 in proportion to their power of resisting this 

 molecular carriage. Edison, after a long se- 

 ries of experiments, decided in favor of a natu- 

 ral fiber, and, of all the hundreds of fibers that 

 he tried, a certain species of bamboo found in 

 China proved the best. The process by which 

 the fibers are carbonized differs with each pat- 

 entee. Edison cuts the strips of his bamboo 

 four inches long by one eighth of an inch wide, 

 by one sixty-fourth of an inch thick. This strip 

 he bends in loop-shape around a mold. While 

 it is carbonizing, he keeps it in place by weights 

 that allow it to contract. Several of these loops 

 are placed in a plumbago mold and exposed to 

 intense heat for about four hours ; when taken 

 out, each carbon-loop is clamped to the leading 

 wires and sealed in a glass bulb from which the 

 air is exhausted. On the Swan lamp, used by 

 the Brush Company in the United States, or- 

 dinary cotton-thread is employed, to which 

 VOL. xxiv. 20 A 



solidity is given by plunging it into sulphuric 

 acid diluted with one third its volume of water. 

 This u parchmentizes " the cellulose of the 

 thread, making it homogeneous. The prepared 

 thread, bent into a horseshoe-shape with a spi- 

 ral in the middle, is carbonized by placing it in 

 carbon-dust and raising to orange heat. The 

 lamp is completed by inclosing the loop in a 

 transparent glass glo^be in which a vacuum is 

 produced. This lamp gives sixteen to twen- 

 ty candle-power (an ordinary kerosene-burner 

 gives five to six candle-power). The electri- 

 cal resistance of this lump is about iorty ohms, 

 while Edison's is 140. 



Hiram S. Maxim's lamp has the general feat- 

 ures of those described above, except that the 

 filament used is stamped from a flat sheet of 

 paper, in the shape of a letter M, and carbon- 

 ized between sheets of thin paper in iron molds, 

 and afterward treated to render it, as homoge- 

 neous as possible, which is effected by heating 

 the filament to incandescence in a carbona- 

 ceous atmosphere. The gas is decomposed 

 by the heat of the incandescent filament, on 

 which the liberated carbon is deposited. The 

 thinnest parts become most heated and de- 

 compose the greatest amount of gas, and con- 

 sequently receive the heaviest deposit. This 

 tends to build up the carbon evenly, which is 

 the great object in making the filament. 



The incandescent lamps covered by the Wes- 

 ton patents were exhibited in great profusion 

 at the exposition. The carbon of these lamps 

 has a zigzag shape, and is made from cellulose 

 by a process not yet made public. The result- 

 ing material is, 'before carbonizing, a translu- 

 cent, elastic substance, and produces an exceed- 

 ingly strong, metallic-looking carbon, capable 

 of resisring very high temperatures for a long 

 time. The Weston Company also exhibited an 

 incandescent lamp of one hundred candle-pow- 

 er. It did not differ from their regular lamp 

 in any particular, except that it was of a larger 

 size, the loop being about six inches long. 



The Bernstein lamp also appeared among the 

 exhibits. Tne carbons of this lamp are tubular 

 and bent into the form of a loop. They are 

 made by carbonizing a finely woven cotton or 

 silk fabric. The Gerard lamp's filament con- 

 sisted of two fine carbon rods having the lead- 

 ing wires cemented to one end of each rod. 

 The two other ends are cemented together. 

 This is burned in a vacuum and looks like the 

 letter V, when the lamp is hanging down ward. 

 A miniature lamp for dental and surgical op- 

 erations was exhibited. This is only half an 

 inch long, and has a carbon-loop of paper. 



The currents used for incandescent lamps 

 are usually of lower electro-motive force than 

 are used in the arc-lamp. The lamps in all 

 systems are connected in multiple arc, and any 

 number can be burned on one circuit. About 

 twenty-four incandescent lamps were fed by 

 the Brush storage-battery. Each gave a steady, 

 soft light of about fourteen candle-power. 



Dynamos. Numerous dynamos were exhibit- 



