on the Magnetic Needle. 387 



pole of the needle which is near it, M. Arago conceives that 

 it is impossible to attribute it to any magnetism of the disc, 

 since it is known that, in whatever way a needle acts upon ano- 

 ther body, in order to communicate to it its magnetic proper- 

 ties, it can only give it a magnetism from which there will 

 arise an attractive force. * 



At a meeting of the Academy of Sciences, held on the 10th 

 July, M. Arago continued the account of his magnetic expe- 

 riments. He announced that he had made experiments from 

 which it resulted that, for certain positions of a vertical needle, 

 and for velocities of rotation sufficiently rapid, the repulsive 

 force which is exerted in the direction of the radius is as great 

 as the force perpendicular to the radius, the effects of which 

 are observed upon a horizontal needle. 



M. Poisson having stated, in his memoir on the theory of 

 magnetism in motion, (of which we shall give some account in 

 the next article,) that Coulomb had recognised the magnetic vir- 

 tue in all bodies, independently of the iron which they contain, 

 M. Arago remarked that the idea of Coulomb was quite differ- 

 ent from his, Coulomb having been of opinion that a quantity 

 of iron too small for chemical analysis even to appreciate, was 

 yet sufficient to produce in bodies which contained it appre- 

 ciable magnetic effects. MM. Thenard and Laplace confirm- 

 ed this remark, and M. Poisson said that he would suppress the 

 assertion, which he had made without attaching to it any im- 

 portance. 



In justice to M. Arago, we have given the above statement 

 as we find it : but injustice to M. Coulomb, it is necessary 

 to remark, that he is the undoubted author of the discovery 

 that all bodies, whether organic or inorganic, are sensible to 

 the influence of magnetism. M. Biot f has remarked, that there 

 are two ways of explaining this, either all substances in nature 

 are susceptible of magnetism, or they all contain portions of 

 iron, or other magnetic metals, which communicate to them this 

 property. This last explanation, though adopted by Cou- 



• M. Ampere stated to the Academy his opinion that the action of the 

 disc on the needle is always repulsive, and he ascribes the apparent attrac- 

 tion which is manifested, when the needle is placed at two-th.rds ot 

 the radius, to the action of the cxccntric part of the disc. 



t Traiti- tie Physique, Tom. iii. p. 117. 



