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PROCEEDINGS OF THE AMERICAN ACADEMY. 



rent had been sent instantaneously through the coil at the time t = 0. 

 For a galvanometer of the same period with practically no damping the 

 value of A/A under the circumstance just mentioned would be about 

 0.9964. A current of the form 1= k (r — t) and lasting for 34 seconds 

 would, in the case of the galvanometer W, give a throw within about one 

 third of one per cent the same as an impulsive discharge of the same total 

 amount would cause if sent through the coil at the origin of the motion. 



Figure O. 



For a current of the general shape of S (Figure G) regarded as stop- 

 ping at the time t = t, the ratio of A/A would be much more nearly 

 unity than for a current of the form I = k (t — i). 



If as in the case of an induction coil without iron, when the primary 

 circuit is suddenly broken, / is of the form I ■ e~ kt , and if we write 

 g = a — k, 



JRQ = ° 2 [> T (p ■ sin P t + g- cos P r) - g], 



(52) 



