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PROCEEDINGS OF THE AMERICAN ACADEMY. 



comparatively easy, however, to give to the galvanometer coil, by aid of 

 a large induction apparatus with air core, such a series of given impulses 

 at given time intervals as shall give all necessary information. In fact 

 the simple device of determining the throw due to two equal impulses 

 separated by the interval r for a number of different values of r will 



Figure G. 



The curves Q, R, S represent for different relative values of the mutual in- 

 ductance the current induced in the secondary circuit of a certain induction coil 

 without iron, when the primary circuit is suddenly closed. 



usually serve to decide sharply whether or not the galvanometer coil 

 follows the Gaussian law closely enough to make it possible to predict 

 its behavior under ordinary circumstances from the equations proved 

 above. This kind of experiment was made with Galvanometer V : an 

 adjustable commutator, driven through a train of wheels by a motor 

 running very steadily at just under 30 revolutions per second, served 

 to give the impulses at the right time interval apart. A series of 



