82 Prof. CErsted's Experiments on Diamagnetism, 



height, applied to the discovery of diama^netism the observa- 

 tion, overlooked by other philosophers, that the two poles of 

 the magnet employed together do not produce on these bodies 

 a repulsion equal to the sum of the repulsions produced by 

 each of them, but equal to their difference; so that their joint 

 effect is null when their forces are equal. At the same time 

 he made some experiments which seemed to indicate that the 

 pole which repulsed the diamagnetic body produced in the 

 parts adjacent to it a magnetic force similar to its own, but 

 not an opposite force, as occurs in attracted bodies. Prof. 

 Weber* confirmed the opinion of M. Reich by some very 

 elaborate researches, and showed that diamagnetic bodies ac- 

 quire, under the influence of the electro-magnet, a transversal 

 magnetism having two poles, but so placed that each of them 

 has the same kind of magnetism as the pole nearest to the 

 electro-magnet. 



M. Poggendorff conceived some very decisive experiments, 

 which have the advantage of proving the new view in an easy 

 manner; and M. Pliicker contributed a further experiment, 

 which, if it did not tend to establish the view, rendered the 

 possibility of proving it more easy. 



In my experiments I made use of the large U-shaped elec- 

 tro-magnet of the Polytechnic School of Copenhagen, which 

 is capable of carrying 1400 kilogrammes f. It must, how- 

 ever, be remarked, that it was not necessary to put all its force 

 in activity for these experiments; but there was rarely less 



* See Taylor's Scientific Memoirs, vol. v. Part 19, p. 477- 

 f I have here conformed to the usual way of indicating the power of the 

 magnet, although there is much uncertainty, as is proved by my experi- 

 ments on this electro-magnet, conmiunicated to the Society in December 

 1847. The object of these experiments was to ascertain the weight the 

 electro-magnet was capable of carrying when its poles were furnished with 

 different pieces of iron. Within certain limits the carrying force increased 

 nearly in proportion to the mass of the keeper ; but what merits most 

 attention is, that the force of the electro-magnet expressed in weight does 

 not follow the same relation to the electro-motive power of the galvanic 

 apparatus, when the keeper is in contact with the electro-magnet, and when 

 it is at a certain distance. In contact, the mean effect of each galvanic 

 element was 712'5 kilogrammes. But two elements combined gave but 

 0'72 of the sum of the individual effects of the elements ; three elements 

 combined gave but 0-48; eight, 0-26 ; sixteen, 0-125; so that the effect of 

 sixteen elements was only twice that of one. At the distance TSS millim. 

 the effect of one element was only 0-1 78 of that of the same element in the 

 case of contact, but the effect increased in a very different ratio with the 

 number of the elements; in this case sixteen elements gave four times the 

 effect of a single one. At 2-225 millims. distance the effect of one element 

 was only 0-051 of that produced in case of contact; but sixteen elements 

 gave 9-4 times the effect which a single one gave. These experiments, 

 which require much time, I intend to continue as soon as my other engage- 

 ments will allow. 



