1821.1 Prof . Oersted on Electro-magnetism. 327 



the experiment as before. 1 had the same result, with this differ- 

 ence only, that the effect was rather weaker. 



When a light magnetic needle is placed upon a large conduc- 

 tor throuo-hwhich a strong discharge is passed, its direction is 

 almost entirely determined by the electro-magnetic effect, and 

 the magnetism of the earth causes but a very slight direction. 

 Let A B C D, fig. 4 b, represent the large conductor, and suppose 



— e to enter at A C, and + e at B D ; the direction of the elec- 

 tro-magnetism may then be marked by the signs + £ — e. 

 Place a magnetic needle S N properly mounted above the 

 conductor, and let us call the end of it which turns towards the 

 south pole s, and that which turns towards the north n ; this 

 beino- done, it will be found that the direction s n will coincide 

 with°the direction + e — s. If the needle held always in the 

 same horizontal plane be put towards one of the sides of the 

 conductor, the north pole will be repelled from the side A B, 

 but attracted by the side C D, only much more feebly than before. 

 The cause of this phenomenon is undoubtedly that every point in 

 that half of the needle which turns to the north is repelled by 



— b coming from the south, and attracted by + s coming from 

 the north. In every point of the conductor, there is, therefore, 

 an effort to act magnetically in two different directions. 



M.Prechtel, of Vienna, a distinguished chemist, has succeeded 

 in representing the phenomena of the galvanic conductor by 

 means of iron wire turned into a spiral form, which he touches 

 with the magnet in the same manner as if he were magnetising 

 a cylinder. This spiral thus gains transverse poles, but no sen- 

 sible polarity from one end to the other. By employing the 

 requisite means, each coil of the spiral has more than two poles 

 given to it, and it will then produce the same effects as the con- 

 necting wire upon the magnetic needle. This experiment has 

 led him to consider the connecting wire as a transverse magnet, 

 having a great number of successive poles, which are alternately 

 north and south. It will be observed that we have arrived by 

 different routes at opinions which are almost entirely similar. 

 I prefer, however, to keep the name of electro-magnetism for 

 the state of the connecting wire ; for in the first place, there is 

 no distinct pole in such a conductor ; and besides this, the con- 

 tinual production of fresh electricity in the galvanic apparatus 

 requires that we should suppose the electro-magnetism to be con- 

 tinually renewed, and an uninterrupted circulation of electrical 

 forces in the conductor. In order that magnetism, properly so- 

 called, may be exhibited, it is requisite that the circulation 

 should be interrupted, without the contrary effects of the activity 

 which existed in the conductor, being suspended. 



