ELECTRIC LIGHTING, PROGRESS OF. 



275 



ments on which were very incomplete, gave but 

 32 carcels in the former and 14 in the latter case. 



The following is the complete report of the 

 8uh-committee on incandescent lamps, with the 

 exception of the detailed statement of the per- 

 formance of each lamp, which is omitted, as not 

 essential to a full understanding of the results 

 obtained : 



I. DESCRIPTION or THE LAMPS. The only 

 lamps in the exhibition which were purely in- 

 candescent in character were those of Edison 

 and Maxim, in the United States Section, and 

 those of Swan and Lane-Fox, in that of Great 

 Britain. The idea represented in these lamps 

 is essentially the same in all of them, the differ- 

 ences being, for the most part, details of con- 

 struction. They all consist of a glass envelope 

 more or less spherical in form, in which is in- 

 closed a carbon loop, made of carbonized or- 

 ganic material, and supported upon wires of 

 platinum sealed into the glass. The space in 

 the interior of the lamp is very perfectly ex- 

 hausted. 



A. The Edison Lamp. The Edison lamp is 

 pear-shaped in form. The carbon filament is 

 long and fine, and is bent into the shape of a 

 U. It is made from Japanese bamboo, cut to 

 the requisite size in a gauge. In section it is 

 nearly square, being about 0'3 millimetre on a 

 side, the ends being left considerably wider. 

 The fiber is carbonized in molds of nickel, and 

 is attached to the conducting wires by copper, 

 electrolytically deposited upon them. 



B. The Swan Lamp. The Swan lamp is 

 globular in form, the neck being quite long. 

 The carbon filament is made from cotton-thread 

 parchmentized before carbonization by treat- 

 ment with strong sulphuric acid. The ends of 

 this filament are very much thickened, and the 

 loop has a double turn at the top. Its ends are 

 clamped in a pair of metal holders, supported 

 laterally by a stem of glass which rises through 

 the neck to the base of the globe. Below, 

 these holders are fastened to wires of platinum 

 which pass through the glass. 



C. The Maxim Lamp. The Maxim lamp is 

 also globular in form, but it has a short neck. 

 Within the neck rises a hollow cylinder of glass, 

 supporting upon its summit a column of blue 

 enamel, through which pass the conducting 

 wires of platinum which carry the carbon. 

 The filament is made from card-board cut by a 

 punch into the form of an M. In section, there- 

 fore, it is rectangular, and several times as broad 

 as it is thick. It is carbonized in a mold through 

 which a current of coal-gas is passed. After 

 carbonization, the filament is placed in an at- 

 tenuated atmosphere of hydrocarbon-vapor and 

 heated by the current. The vapor is decom- 

 posed, and its carbon is precipitated upon the 

 filament. In this way not only are inequali- 

 ties obliterated, but the resistance of the fila- 

 ments may be equalized, and brought to any 

 standard required. 



D. The Lane - Fox Lamp. The Lane - Fox 

 lamp is ovoid in shape, the neck being in length 



intermediate between the two lamps last de- 

 scribed. The carbon is in the form of a horse- 

 shoe, and is circular in cross-section. It is 

 made from the root of an Italian grass, largely 

 used in France for making brooms. After 

 carbonization, the filaments are classified ac- 

 cording to their resistances. They are then 

 heated in an atmosphere of coal-gas, by which 

 carbon is deposited upon them, as in the fila- 

 ments of the lamps last described. The fila- 

 ment in the lamp is supported by platinum 

 wires, to which it is attached by sleeves of car- 

 bon encircling both. These wires pass through 

 tubes in the top of a hollow glass stem. Just 

 below the extremities of these tubes are two 

 small bulbs containing mercury, forming the 

 contact between the platinum wire sealed into 

 the glass above and the copper conductor which 

 enters from below. These conductors are held 

 in place by plaster which fills the base of the 

 lamp. 



II. METHODS OF MEASUREMENT. The ques- 

 tion to be determined was simply the efficiency 

 of these lamps. The efficiency of a lamp is the 

 ratio of energy produced to energy consumed, 

 i. e., the quantity of light given by the lamp 

 for each horse-power of current which it con- 

 sumes. The data required to calculate this 

 efficiency may be obtained when the electro- 

 motive force of the current, the resistance of 

 the lamp when giving its light, and its illu- 

 minating power have been determined. 



1. Electro-motive Force. The electro-mo- 

 tive force, or fall of potential through the lamp, 

 was measured by Laws's method. A suitable 

 condenser was charged by being put in com- 

 munication with a standard Daniell cell, and 

 then discharged through a high-resistance gal- 

 vanometer, the deflection of the needle being 

 noted. This condenser was then connected to 

 the two wires of the lamp, and again dis- 

 charged through the galvanometer, the deflec- 

 tion being made the same as before by means 

 of a variable shunt connected with the galva- 

 nometer. Since with a given condenser the 

 charges it receives are proportional to the po- 

 tentials of the charging currents, and since the 

 discharge deflections of a galvanometer repre- 

 sent the quantity of these charges, it follows 

 that the electro -motive forces are proportional 

 to these discharge deflections. If, however, 

 as in the present case, the discharge deflections 

 are made equal by means of shunts, then the 

 electro-motive forces are proportional to the 

 multiplying power of the shunts. 



2. Resistance. The resistance of the lamp, 

 when giving its light, was obtained by making 

 the lamp one side of a Wheatstone's bridge 

 through which the main current was flowing. 

 The second and fourth sides were formed of 

 fixed resistances of known value, and the third 

 side of an adjustable resistance. When the 

 bridge is balanced, the product of the two fixed 

 resistances, divided by the adjusted resistance, 

 gives the resistance of the lamp at the given 

 candle-power. 



