Experiments with Open Circuits. 55 



tion being of opposite sign to that produced when the secondary 

 circuit is closed. 



When, however, the coil is arranged according to the scheme 

 ABODE F, and the ends A and F are connected with the plates 

 of a condenser of large capacity, so that now the coil itself 

 possesses little or no electrostatic capacity, then the currents 

 will evidently be much less local than before, and will pro- 

 bably be pretty uniform throughout the coil. Thus L 2 , the 

 coefficient of self-induction of the secondary circuit, will be 

 greater than it was, and will probably not differ very much 

 from L x , the coefficient of self-induction of the primary cir- 

 cuit, as the coils are of approximately equal length ; and 

 since the capacity of the condenser in the secondary is 

 large, C 2 will be greater than it was in the former case, when 

 it was the electrostatic capacity of the coil itself. Thus both 

 L 2 and C 2 are larger than they were before, and consequently 

 the free period of electrical vibration in the secondary circuit 

 will be much nearer the period of the electromotive force ; 

 thus the denominator in the expression for the current x will 

 be much smaller than it was, or the current will be much 

 greater. This agrees with the experiment last described, which 

 showed that the diminution in the magnetization of the needle 

 due to the introduction of a condenser into the primary was 

 much less in this case than it was before. When there is no 

 condenser in the primary, the equations to determine the 

 initial currents are much the same, whether the secondary 

 circuit be open or closed, the only difference being that when 

 the secondary is open, as the currents are local and not the 

 same all along the coil, the coefficients of self-induction and 

 mutual induction will be less when the secondary is open 

 than when it is closed ; and as Lord Rayleigh has proved that 

 in a secondary with a few windings of wire, a needle is mag- 

 netized more strongly than in one of more windings, we should 

 expect, if there were only one of these local currents, that a 

 needle placed in it would be magnetized more strongly than 

 when the circuit was closed. The existence of several of these 

 local currents complicates the question, and reduces, of course, 

 the intensity of each of them. In some cases, however, the 

 reduction of the intensity from this cause is not sufficient to 

 counterbalance the increase due to the other cause, as in the 

 case last described, when the needle vibrated twice as quickly 

 after being placed in the open circuit as it did after being 

 placed in the closed. It must be remembered, too, that when 

 the secondary is open, the currents are oscillatory, and so arc 

 first in one direction and then in the opposite; this musi have 

 the effect of diminishing their magnetizing-power, though we 



