PHYSICS. 6 ( y 



ual lamps are iiidcpeudeut of each other, aud lamps of different systems 

 may be used simultaneously. {Nature, February, 1881, xxiii, 373.) 



Sir William Thomson communicated to the British Association at 

 York the results of measurements made by himself and by Bottomley 

 upon the illuminating power of incandescent vacuum lamps. The 

 lamps used were of the Swan pattern, and the current was furnished 

 by Faure secondary batteries. The electromotive force at the termi- 

 nals of the lamp was determined by a galvanometer of very high resist- 

 ance; the current strength by one of low resistance; and the candle- 

 power by comparing the shadows of a pencil cast by the lamp and by a 

 standard candle on a sheet of white paper. With 26 cells the electro- 

 motive force was 5G.9 volts, the current 1.21 webers, and the candles ll.G; 

 thus giving 6.SS kilogram-meters per second for the work done in the 

 lamp, or 0.093 horse-power. This would give 125 candles per horse- 

 power of current. At 25 candles the economy rose to 194 candles per 

 horse-power; at 38 to 22-4 candles per horse-power; at 55 to 294 can- 

 dles; at 82 to 349; at 102 to 382; at 117 (another lamp) to 316; at 189 

 to 440. Lamp No. 1 gave at GO candles an economy of 295 ; No. 2, at 68 

 caudles, one of 234; and No. 3, also at G8, one of 219 candles per horse- 

 l)ower. {Xature^ SeiJtember, 1881, xxiv, 490.) 



