244 Lord Rayleigh on the Behaviour of Iron and Steel. 



The resistance of each wire is 3*2 ohms ; and thus when 

 two Grove cells are used in connection with one of the wires, 

 a current of about an ampere (•! C.G.S.) can be commanded. 

 Smaller currents were obtained by the insertion of resistances 

 from a box. 



Although the secondary coil, connected with a delicate 

 galvanometer, contained a large number of convolutions, the 

 sensitiveness was insufficient to allow of the small magnetizing 

 force being taken as low as would otherwise have been de- 

 sirable. It was obtained by means of the second wire of the 

 helix, which w r as included in the circuit of a Daniell cell and 

 200 ohms from a resistance-box. When the circuit was com- 

 pleted (or broken) at a key, the force brought into operation, 

 or removed, was 



ggJ--H0.O.S. 



In making a series of observations it was usual, after each 

 alteration of the strong magnetizing force, to apply and re- 

 move the small magnetizing force several times before 

 attempting to take readings. 



The results obtained by this method were of a pretty de- 

 finite character. The small force produced a constant effect 

 upon a wire of unannealed Swedish iron, 3*3 millim. in 

 diameter, until the large force was increased from to about 

 5 C.G.S. At about 10 C.G.S. the effect of the small force 

 fell off 5 per cent. The highest force used, about 29 C.G.S., 

 reduced the effect to about 60 per cent, of its original amount. 

 On complete removal of the force due to the Grove cells, there 

 was but a partial recovery of effect, doubtless in consequence 

 of residual magnetization. After the w r ire had been removed 

 from the helix and well shaken, the small force was found to 

 have recovered its full efficiency. 



The wire was then annealed and submitted anew to a similar 

 series of operations. The magnetization due to the alternate 

 application and removal of the small force was found to be at 

 first, i. e. in the absence of a constant force, twice as great as 

 before *. 



The increase, however, is not long maintained, a steady force 

 of 2 C.G.S. being already sufficient to cause a marked falling 

 off (of about 20 per cent.) , Under the operation of 29 C.G.S., 

 the effect of the small force fell to about \ of its original 



* It should here be remembered that any part of the change of mag- 

 netization which lags behind for more than a second or two, fails to 

 manifest itself fully in the indications of the galvanometer. 



