OP ARTS AND SCIENCES. 



241 



Several series of measurements were made with currents of widely 

 different strengths, and with the thinnest and the thickest of the dia- 

 phragms used in these experiment.^, in order to ascertain whether the 

 induced current in the measuring coil was proportional to the inducing 

 line current, and since this was found to be sensibly the .case, the 

 strength of six milliamperes was adopted, as already stated. 



Considerable trouble was experienced in obtaining satisfactory con- 

 secutive readings of the deflections, on account of the close proximity 

 of the laboratory to the streets, rendered especially disturbing by the 

 presence of the electric railway. The difficulty was avoided as far as 

 VOL. XX v. (n. s. xvii.) 16 



