TO TIIK MOVEMENT OF MACIIINI'.S. 17 



a kind of anti-magnetism ! I have not succeeded in confirming 

 this discovery by the following experiment. In the first place I 

 considered it necessary to exclude the weakening effects, which 

 constantly take place when a second uniting wire is introduced 

 into a closed circuit ; and it is easy to attain this by employing 

 also another battery, which is placed in contact with the extremities 

 of the interior helix. Now the hollow tube having been rendered 

 magnetic by a surrounding helix, a considerable quantity of iron 

 filings adhered to the poles. The contact of the interior helix, 

 with its own battery, was then established. Not a single grain of 

 the filings fell off, whatever was the direction of the current ; — a 

 proof that more experiments are requisite on the part of M. 

 Parrot to confirm this discoveiy. This is also another experi- 

 ment, which proves incontestably that the inner surface of a hol- 

 low cyUnder is entirely deprived of magnetism (29). The two 

 extremities of an inner helix were placed in contact with a very 

 delicate galvanometer ; the cylinder was then attached as arma- 

 ture to a horse-shoe sti'ongly magnetized. The adherence was 

 veiy powerful, and yet the needle was not in the least affected. 

 But when one of the ends of a small bar of soft iron was intro- 

 duced into the inner helix, the needle was greatly agitated as 

 soon as the other extremity was placed in contact mth one of the 

 poles. The hollow cylinder had been rendered magnetic by a 

 surrounding coil ; there was in this case also no deviation of the 

 galvanometer placed in contact with the interior coil, 



37. 

 To these observations relating to soft iron magnetized by in- 

 fluence, it is necessarj' to add a few words mth respect to steel, 

 this being endowed with a coercitive force, supposed to be n\ill 

 in soft iron. Subjected to inductive currents, sufficiently enei'- 

 getic to ovei'power this resistance, steel retains the magnetic con- 

 dition which the currents have caused it to adopt, even when 

 these latter have disappeared. In fact, cui'rents of short dura- 

 tion, which have no influence on soft iron, magnetize consider- 

 ably tempered steel. If we refer to the soft iron wire subjected 

 to the experiment, described in Art. 34, the wire does, it is true, 

 become magnetic, but the magnetism cannot be developed in pre- 

 sence of the helix, which is endowed with a contrary magnetism. 

 If these two portions could be separated, there would be an 

 evident magnetization ; but tliis cannot be effected, as the mag- 



VOI . II. PART v. B 



