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PROCEEDINGS OF THE AMERICAN ACADEMY 



Wilde Machine (large size). 



The measurements with the Wilde machine were made with an elec- 

 trodynamometer similar to that described in Maxwell's " Electricity and 

 Magnetism." It was constructed on the Helmholtz Gaugain principle, 

 and had a resistance of 58.9 ohms. A shunt of .1 ohm had to be 

 employed, and the instrument was also coupled in multiple arc to 

 avoid the lengthening of the bifilar suspension. 



Gramme Machine (large size). 



Siemens Machine (large size). 



I add a few data in regard to the dimensions of these machines, 

 which are partly taken from the reports of the Secretary of the Navy 

 for 1877, and partly from the Station records which were generously 

 placed at my disposal. 



