202 



HENRY A. ROWLAND 



lamp and thermometer. The calorimeter and cover weighed 0-103 

 kil. and the lamps about 0-035 kil. 



First experiment, No. 201 in calorimeter and No. 580 in photometer; 

 capacity of calorimeter = 1-153 + -009 + -007 = 1-169 kil. The 

 temperature rose from 18 -28 C. to 23 -11 C. in five minutes, or l-75 

 F. in one minute. Taking the mechanical equivalent as 775-, which is 

 about right for the degrees of this thermometer, this corresponds to 

 an expenditure of 3486 foot pounds per minute. The photometric 

 power of No. 580 was 17-5 candles maximum, or 13-1 mean, /. 



When the lamps were reversed, the result was 3540 foot pounds for 

 No. 580, and a power of 13-5 or 10-1 candles mean. The mean of 

 these two gives, therefore, a power of 3513 foot pounds per minute for 

 11-6 candles, or 109-0 candles to the horse power. 



To test the change of efficiency when the temperature varied, we 

 tried another experiment with the same pair of lamps, and also used 

 some others where the radiating area was smaller, and, consequently, 

 the temperature had to be higher to give out an equal light. 



We combine the results in the following table, having calculated the 

 number of candles per indicated horse power by taking 70 per cent of 

 the calculated value, thus allowing about 30 per cent for the friction 

 of the engine, and the loss of energy in the magneto-electric machine, 

 heating of wires, etc. As Mr. Edison's machine is undoubtedly one of 

 the most efficient now made, it is believed that this estimate will be 

 found practically correct. The experiment on No. 817 was made by 

 observing the photometric power before and after the calorimeter 

 experiment, as two equal lamps could not be found. As the fibre was 

 round, it gave a nearly equal light in all directions as was found by 

 experiment. 



