62 

 ELECTEICAL MEASUREMENTS 



BT HENRY A. ROWLAND AND THOMAS DOBBIN PENNIMAN 

 [American Journal of Science [4], VIII, 35-57, 1899] 



In a previous article * mention was made of some work then being 

 carried on at the Johns Hopkins University to test the methods for 

 the measurement and comparison of self -inductance, mutual inductance, 

 and capacity there described. 



In the present paper, there will be given an account of the experi- 

 ments performed with some of the methods described in the previous 

 article, together with a method for the direct measurement of the 

 effect of electric absorption in terms of resistance. 



The methods that were tried were 25, 26, 9, 3, 12 and 6. 



Description of the Electrodynamometer, Dynamos, Coils, Condensers, 

 Resistances and Connections used in the Experiments 



Electrodynamometer. The electrodynamometer was one constructed 

 at the University, having a sensitiveness, with the coils in series, of 1 

 scale division deflected for -0007 ampere. 



The hanging coil was made up of 240 turns of No. 34 copper wire B 

 and S gauge. The coil was suspended by a bronze wire connected with 

 one terminal of the coil. The other terminal of the coil was a loop of 

 wire hanging from the bottom of the coil and attached to the side of 

 the case; both the suspension and the loop were brought out to binding 

 posts. The resistance of the coil with suspension was 21-7 ohms. 



The fixed coils were made up of 300 turns each of No. 30 B and S 

 gauge copper wire. The coils were wound on cup-shaped metal forms 

 and soaked in a preparation of wax. The form was then removed and 

 the coils placed a radius apart as in the arrangement of Helmholtz. 



Dynamos. There were two dynamos used, a Westinghouse alter- 

 nator, and a small alternating dynamo constructed at the University. 



Journal, iv, p. 429, December, 1897; Philosophical Magazine, January, 1898. 



