APPENDIX. 
Arr. XLI. — On the Efficiency of Edison's Electric Light; by 
Professor H. A. RowLAND of the Johns Hopkins University, 
and Professor GkorGE F. Barker of the Univ. Pennsylvania. 
mic 
last, can undoubtedly be put into practical shape. 
Three methods of testing the efficiency presented themselves’ 
tous. The first was by means of measuring the horse power 
ber of 
ro 
and so this method was abandoned for the third one. This 
method consisted in putting the lamp under water and observ- 
ing the total amount of heat generated in the water per minute. 
For this purpose, a calorimeter, holding about 14 kil. of water, 
was made out of very thin copper: the lamp was held firmly 
Mm the center, so that a stirrer could work around it. e tem- 
col1c noted on a delicate Baudin thermometer graduated 
O . 
s the experiment was only meant to give a rough idea of 
the efficiency within two or three per cent, no correction was 
made for radiation, but the error was avoided as much as pos- 
sible by having the mean temperature of the calorimeter as 
hear that of the air as possible, and the rise of temperature 
small. The error would then be much less than one per cent. 
