496 



PROCEEDINGS OF THE AMERICAN ACADEMY 



This machine is built somewhat after the style of the old Edison Z 

 machine. It is series-wound and has about the resistance (hot) of an 

 Edison incandescent lamp, old style. The dynamo is an exceedingly 

 neat and smooth runniu2^ machine. The motor runs without vibration 

 and with no sparking, and heats up but very little even at the highest 

 speed. It has been run for two minutes at a speed of 10,000 revolu- 

 tions per minute. The great speed here obtained by such simple 

 means, together with the readiness with which it can be varied within 

 wide limits, indicates the availability of such a motor in any physical 

 experiments in which a great speed of revolution is needed, as in 

 studies of the velocity of light, the duration of the electric spark, etc. 



TABLE II. 



One of the chief advantages derived from the use of electro-motors 

 is the small weight per horse-power developed. The motors which 

 we have tested, with one exception, the Gramme " Machine a petite 

 lumiere," have been intended for doing very light work, and the 

 efficiency exhibited is not of course nearly as high as would be shown 



