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PROCEEDINGS OF THE AMERICAN ACADEMY. 



coil of the large ballistic gahanometer, was usually considerable and 

 the strain upon the insulation of the wire was sometimes large when a 

 powerful current in the primary circuit was suddenly reversed. Occa- 

 sionally, there seemed to be some leakage in this circuit, so we intro- 

 duced a number of condensers into the circuit in the attempt to reduce 



Figure 7. This figure shows the forms of the curves obtained by plotting 

 the permeability and the susceptibility of a certain kind of soft iron against 

 the exciting field. These curves, OBZ, OAX, are drawTi to different scales. 



the stress. What the exact eflPect of such condensers in a complex 

 circuit will be when the breaking arc in the primary circuit is oscilla- 

 tory, it is usually impossible to predict, because some necessary data 

 are wanting or because the literal equations are of too high a degree 

 to be solved, but certain general facts are clear. The following analy- 

 sis treats some questions, as applied to a circuit taken for illustration, 

 which are really, perhaps, too elementary to need any discussion. 

 Figure 6 represents two neighboring circuits: — 



(a) A primary circuit of total resistance R, and total self inductance 

 L, which contains a constant battery of voltage, V, and carries a 

 current /. This circuit is furnished with a gap (0) which may be 

 closed or opened at pleasure. 



(b) A secondary circuit of several branches, which has no battery, 



