453 



means admit that, because " it becomes more magnetic by compres- 

 sion, we must conclude that the loss of magnetic medium from its 

 interstices is more than supplied by the magnetic matter which takes < 

 its place ;" for, according to what has already been advanced, the 

 excess of the attraction of the material particles above that of the 

 medium they displace is the same after, as it was before compression ; 

 inasmuch as compression merely changes the relative situations of 

 the particles, by bringing them closer together, but does not in the 

 least alter their volume, and consequently does not in the least alter 

 the quantity of medium they displace. 



With respect to carbonate of lime, Professor Williamson's con- 

 clusion is, of course, untenable, because it is based upon the fore- 

 going one. He says, " when these" particles are brought closer 

 together by pressure, with diminution of the intervening spaces oc- 

 cupied by the medium, the mass becomes more diamagnetic, because 

 a certain quantity of the magnetic medium is thus replaced by the 

 less magnetic matter." It is, however, manifest that exactly the 

 same quantity of magnetic medium is displaced by the less magnetic 

 matter after, as there was before compression. Why, then, should 

 diamagnetic action be increased by compression ? 



Lastly, with respect to the crystals of carbonate of iron and car- 

 bonate of lime, Professor Williamson's explanation, although inge- 

 nious, is liable to the same objections as those already mentioned. 

 It cannot, in fact, be said that the functions of matter predomi- 

 nate most strongly over those of the medium they displace in any 

 one direction, merely because the particles may be closer together in 

 that direction ; for, as long as each particle is surrounded by the 

 medium, the predominance of that function of the particles with 

 which we are concerned, i. e, their attraction, over that of the me- 

 dium they displace will be the same, whatever may be the distances 

 of the particles asunder. 



From the foregoing remarks, therefore, it is manifest that, if Pro- 

 fessor Tyndall has not yet succeeded in demonstrating that the 

 hypothesis of the existence of a magnetic medium and of the iden- 

 tity of magnetism and diamagnetism is necessarily at variance with 

 experimental facts, neither has Professor Williamson succeeded in 

 proving that this hypothesis is in accordance with those facts. The 

 question of the existence of a magnetic medium is still an open one. 



