of Magnetism : mth Notes by Mr. Faraday. 407 



it claimed an appropriate apparatus; and after various ar- 

 rangements more or less complicated, we stopped at the fol- 

 lowing, which has the advantage of being very successful and 

 very simple. 



The whole of the contrivance is attached to the lifter of the 

 magnet. This piece, which is aparallelopiped, is surrounded in 

 the middle by the electro-dynamic spiral, to which it is firmly 

 attached by two pieces of brass, so that the latter can enter 

 between the magnetic poles whilst the lifter comes in contact 

 with the poles in the ordinary way. The extremities of the 

 spiral come in contact one with each magnetic pole bj' means 

 of two little springs in the form of wings attached to the lifter, 

 and which press slightly against the poles when the lifter is 

 in its place. To leave room for these springs, the lifter is 

 narrower than usual, covering about half the poles; the re- 

 maining space serves for the contact of the springs, which are in 

 this way isolated as it were from the lifter; and yet by means 

 of the magnet itself serve to complete the electro-dynamic 

 circuit. Suppose that the lifter is in its place, the springs 

 touch the poles, and the circuit of tlie spirals is metallically 

 closed by the magnets : on detaching the lifter, the circuit 

 opens in two places ; and either at the one or the other inter- 

 ruption the spark almost constantly appears. When the 

 effect does not take place, it is because the separation has not 

 been well effected; but it is so easy to repeat the experiment, 

 that it is useless to think of a piece of mechanism to remedy 

 an inconvenience which is so easily remedied. 



In this apparatus the spiral on the lifter was of copper. On 

 substituting an iron wire the spark also occurred. This ex- 

 periment was interesting in illustration of any influence which 

 the ordinary power of the magnet over iron might exert upon 

 the electro-dynamic influence. It did not appear that the one 

 action disturbed the other; but before positively affirming the 

 independence, it will be necessary to obtain other proof, which 

 we shall endeavour to do at a more favoui"able opportunity 

 {Exp.Ees.9. 254..). 



3. Terrestrial Magnetism {Exjy. Bes. 137. 140. &c.). 



We took a paper tube two inches in diameter and four inches 

 long, a C()p))er wire forty metres long was coiled round it, the 

 two ends being left at liberty to connect with the galvanometer ; 

 the tube was trimmed at the ends, so that it could be placed 

 upright upon the table either in one direction or the other at 

 pleasure {Exp. Res. 142.). A cylinder of s(ift iron, as is well 

 known, placed parallel to the dip is subject to the terrestrial 

 ntagnctic influence; the lower part becomes a north pole, the 



upper 



