The Hon. J. W. Strutt on an Electromagnetic Experiment. 433 



This is its maximum value, and is double of that which would be 

 generated by a simple stoppage of the primary current, however 

 sudden. In this way I am inclined to explain the increase of 

 effect produced by the condenser. It is true that, having reached 

 its maximum value, the secondary current rapidly declines and 

 then changes sign ; but from what is known of the behaviour of 

 permanent magnets when submitted afresh to the action of mag- 

 netizing force, it does not seem likely that much disturbance 

 would arise from this cause. 



A more plausible objection may be founded on the exceeding- 

 rapidity of the oscillations, for some time must be necessary for 

 the magnetization of steel. Indeed in our case the period of 

 oscillation is unusually short, on account of the smallness of 



M 2 

 L— ^p When the two circuits are composed mainly of wires 



coiled side by side, L, M, N are approximately equal, and there- 



M 2 



fore L =^- very small compared with either of them. The cur- 

 rent is then transferred, with almost indefinite rapidity, from one 

 wire to the other and back again. 



I made some experiments to examine this point, which will 

 also serve as examples of the general increase of magnetic effect 

 produced by a condenser. The primary current from a Grove's 

 cell was passed through the two wires of coil A joined consecu- 

 tively, and then through one wire of a similar coil B. According 

 as the wires of A are joined, L = 5 or 1. The induced circuit 

 included the other wire of B and the magnetizing spiral, so that 

 N = l and M = l approximately. In the first case, therefore, 



while in the second it is very much smaller. The experiments, 

 conducted in other respects as before, gave the following re- 

 sults : — 



L=5, 



without condenser 



. 16, 



13, 



13, 



14; mean 14. 



L=5, 



with condenser . 



24i 



28, 



81, 



28 ; „ 28. 



L=l, 



without condenser 



• 14, 



15, 



18i, 



14; „ 14. 



L=l, 



with condenser . 



17, 



18, 



19, 



21; „ 19. 



It will be seen that, while without the condenser it made little 

 difference whether L=l or L = 5, the increase produced by the 

 condenser is much greater in the latter case. This is so far in 

 agreement with the explanation just given ; but I confess I should 

 have been better satisfied had the influence of the condenser been 

 less marked when L=l. In order that the reader may better 



Phil. Mag. S. 4. Vol. 39. No. 263. June 1870. 2 F 



