222 



VARIABLE STATE. 



We obtain in the same way the strengths corresponding to 

 momentary contacts; curves I, II, III (Fig. 57), represent the law 

 of the strengths at a point, when contacts are made for durations 

 respectively equal to a, 20, 30. 



0,1 



Fig. 58. 



231. The period T v at which the maximum potential of the 

 wave is obtained for an infinitely short contact, is determined by 

 the condition 



^ = Q, or = 0. 



Since we have 



lit 



the maximum takes place when 2z 2 = 3, or 



2d 



3 



HP 



- X 2 = . 



6 3 



