838 Biclend and Barker 
Efficiency of Edison’s Electric Light. 
than in the plane of the edge. Two observations were taken 
of the photometric power, one in a direction perpendicular to 
the paper, and the other in the direction of the edge, and we 
are required to obtain the average light from these. If Lis the 
photometric power perpendicular to the paper, and / that of the 
edge, then the average A will evidently be very nearly 
A=Lf cos a sin a da +f sin’a da 
$7 47 
A=} L421 
In the paper lamps we found /=4L nearly ; hence A= nearly. 
he lamps used were as follows: 
Approximate 
No. Kind of carbon. Size of carbon. resistance when cold. 
580 paper large 147 ohms. 
901 “se 6é 14 6G 
850 ne small 170°... 7% 
809 ~< de 15s" 
817 fiber large 4 eee 
tometer; capacity of calorimeter = 1153+ -009+ 007=1'169 
kil. The temperature rose from 18°-28 C. to 23°11 C. in five 
pounds per minute. The photometric power of No. 580 was 
175 candles maximum, or 13°1 mean, / 
