22 

 ON THE EFFICIENCY OF EDISON'S ELECTRIC LIGHT 



BY H. A. ROWLAND AND GEORGE F. BARKER 

 \American Journal of Science, [31, XIX, 337-339, 1880] 



The great interest which is now being felt throughout the civilized 

 world in the success of the various attempts to light houses by elec- 

 tricity, together with the contradictory statements made with respect 

 to Mr. Edison's method, have induced us to attempt a brief examina- 

 tion of the efficiency of his light. We deemed this the more important 

 because most of the information on the subject has not been given to 

 the public in a trustworthy form. We have endeavored to make a 

 brief but conclusive test of the efficiency of the light, that is, the 

 amount of light which could be obtained from one horse power of work 

 given out by the steam engine. For if the light be economical, the 

 minor points, such as making the carbon strips last, can undoubtedly 

 be put into practical shape. 



Three methods of testing the efficiency presented themselves to us. 

 The first was by means of measuring the horse power required to drive 

 the machine, together with the number of lights which it would give. 

 But the dynamometer was not in very wood working order, and it was 

 difficult to determine the number of lights and their photometric 

 power, as they were scattered throughout a long distance, and so this 

 method was abandoned. Another method was by measuring the resist- 

 ance of, and amount of, current passing through a single lamp. But 

 the instruments available for this purpose were very rough, and so 

 this method was abandoned for the third one. This method consisted 

 in putting the lamp under water and observing the total amount of heat 

 generated in the water per minute. For this purpose, a calorimeter, 

 holding about 1^ kil. of water, was made out of very thin copper: the 

 lamp was held firmly in the centre, so that a stirrer could work around 

 it. The temperature was noted on a delicate Baudin thermometer 

 graduated to 0-1 C. 



As the experiment was only meant to give a rough idea of the 

 efficiency within two or three per cent, no correction was made for 



