of Magnetism : mth Notes hy Mr. Faraday. 403 



mac^net, the needle of the instrument is in the first place seen to 

 deviate a certain number of degrees, which mdicates a current 

 excited by the magnetism, in the spirals previously made to 

 communicate with the galvanometer. This current lasts but for 

 a moment, and is then completely extinct, as is proved by the 

 needle returning to its first position : this is the second ob- 

 servation. The third (finally) occurs when the spiral is taken 

 from the magnet: the needle of the galvanometer then de- 

 viates on the other side, demonstrating the development ot a 

 current contrary to that excited in the first instance. 



On experimenting with an annular spiral between the poles 

 of a horse-shoe magnet, we observed that the action was much 

 less than that produced with the same spiral when the lifter 

 of the magnet was put to it or suddenly taken from it [^Exp. 

 Res. 34-.). This fact suggested the idea of rolling a copper wire 

 covered with silk round such a magnet, so as to have an ap- 

 paratus always mounted for the experiment in question. 1 he 

 spiral to be subjected to the magnetic influence is then always 

 upon the magnet, and the immediate cause of the phaenomena 

 resides in the lifter, because of the property which that little 

 piece of soft iron possesses of being magnetized and de-mag-- 

 netized rapidly. When the lifter is detached, the spiral which 

 before was in the presence of this piece of iron strongly mag- 

 netized, is suddenly removed from its action, and represents 

 the case of a spiral which having been first approximated 

 to a magnet is then removed. When the lifter is replaced, it 

 is as if a magnet were caused to approach the spiral, for the 

 lifter becomes magnetic on being attached to the poles of its 

 own magnet. 



This arrangement, besides being very active, has the advan- 

 tafre of supplying the philosopher with a constant source of 

 voltaic electricity {Exp.Bes. 46 note). The want of a constant 

 current is often felt in such researches ; and if thermo-magnet- 

 ism offers a plausible means of satisfying such necessities, as 

 I have indicated elsewhere* : yet the new method offered us by 

 a magnet covered with electro-dynamic spirals is not to be de- 

 spised. Here the currents are always ready to be manifested. 

 Suppose, as is usual, the lifter of the magnet is in its place, 

 nothing more is required to obtain a current in the spiral 

 than to detach the lifter, the current in the wire being, as it 

 were, at first in a latent state. 



There are two modes of using this arrangement : the one by 



attaching the lifter ; the other by detaching it. When the two 



• This means consists in having a thermo-electric elementary coinbina- 



lion composed of two metals only, and heated at one juncture to (P Fahr., 



at the other to 212° Faiir.— ylww. dc Chimk; Feb. 1«30, p. 130. 



3 IT 2 motions 



