HERMANN VON HELMHOLTZ 



Thus the primary circuit is always closed ; but the 

 decrease of current at the instant of short-circuiting 

 has the same kind of effect in producing a secondary 

 current as when the primary circuit is completely 

 opened. But because the primary circuit remains a 

 closed circuit, the extra current of self-induction 

 retards the rate at which the current decreases, just as 

 the extra current retards the development of the 

 current at closing. Thus, the conditions under 

 which the secondary currents at closing and at 

 opening are produced are fairly similar ; the intervals 

 of time during which they last are approximately 

 equal ; and the maximum intensities reached by them 

 are almost exactly the same. In this way the opening 

 shock becomes nearly equal to the shock from the 

 secondary coil at the moment of closing. 1 This 

 clever device is a good illustration of the ingenuity 

 of Helmholtz and of his grasp of the technique of 

 electrical experimentation. 



1 For details, see M'Kendrick's Text-Book of Physiology, vol. i., p. 374. 

 Glasgow, 1888. 



