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PROCEEDINGS OF THE AMERICAN ACADEMY 



show this. The difference is in this case not so widely apparent, 

 owing to the extreme weakness of the current used ; it being at this 

 time, in order to get small deflections, the weakest used in the whole 

 of my work. 



These were taken in sets of ten, with wonderfully close means, not- 

 withstanding the apparently great probable error. 



Another series, with a stronger current, gave as the ratio of the 

 results 1.364. 



The results of the investigation are as follows : — 



1. By breaking the primary circuit of an induction coil in a magnetic 



field, the length of spark produced by the secondary coil is more 

 than doubled in length. An application of this fact to the induc- 

 tion coil is suggested. 



2. The results by the different methods used all show an increase of 



electro-motive force when the circuit is broken in a mairnetic 

 field ; and that the etfect cannot be purely a mechanical phenome- 

 non, as M. Becquerel affirms. 



