208 On the Existence of a Magnetic Medium in Space. 



netic weight of the cube would be less than that of the medium. 

 Acted upon in the former direction, the cube would be a neutral 

 body ; acted upon in the latter direction, it would be a diamag- 

 netic body. If the magnetic capacity of the cube diminish still 

 further, it will, according to your hypothesis, become wholly 

 diamagnetic. Now it is evident, supposing the true magnetic 

 excitement to continue, that the cube, when acted on by the 

 magnet in the direction of compression, will approach nearer to 

 the magnetic weight of the medium in which wc suppose it im- 

 mersed, than when the action is across the said line ; and, 

 hence, the repulsion of the cube, when the force acts along the 

 line of compression, must be less than when the force acts 

 across it. 



Reasoning thus from the assumption of a magnetic medium 

 in space, we arrive at a conclusion which can be brought to the 

 test of experiment. So far as I can sec at present, the assump- 

 tion is negatived by this test ; for in diamagnetic bodies the 

 repulsion along the line in which the pressure is exerted i3 

 proved by experiment to be a maximum *. An ordinary mag- 

 netic excitement could not, it appears to me, be accompanied 

 by this effect. 



The subject finds further, and perhaps clearer, elucidation in 

 the case of isomorphous crystals. It is not, I think, questioned 

 at present, that the deportment of crystals in the magnetic field 

 depends upon their molecular structure; nor will it, I imagine, 

 be doubted, that the molecular structure of a complete crystal of 

 carbonate of iron is the same as that of an isomorphous crystal 

 of carbonate of lime. In the architecture of the latter crystal, 

 calcium simply takes the place which iron occupies in the former. 

 Now a crystal of carbonate of iron is attracted most forcibly 

 when the attracting force acts parallel to the crystallographic 

 axisf. Let such a crystal be supposed to diminish gradually 

 in magnetic capacity, until finally it attains a magnetic weight, 

 in a direction parallel to its axis, equal to that of the medium 

 in which we assume it to be immersed. Such a crystal 

 would be indifferent, if the force acted parallel to its axis, but 

 would be repelled, if the force acted in any other direction. If 

 the magnetic weight of the crystal diminish a little further, it 

 will be repelled in all directions, or, in other words, will become 

 diamagnetic ; but it will then follow, that the repulsion in the 

 direction of the axis, if the nature of the excitement remain 

 unchanged, will be less than in any other direction. In other 

 words, a diamagnetic crystal of the form of carbonate of iron 

 will, supposing magnetism and diamagnctism to be the same, 



* Phil. Mag. Sept. 1851. Pogg. Ann. 1851. 

 t Phil. Mag. Sept. 1851. Pogg. Ann. 1851. 



