4*4 Royal Society : — 



This is sufficient to show that, admitting the presence of the me- 

 dium Avithin the cube, the method of argument adopted by Professor 

 Tyndall would not be strictly applicable, unless the density of the 

 internal medium were subjected to limits which the advocates of its 

 existence might possibly be unwilling to grant. 



But it may be asked, if, whilst admitting that the medium may 

 exist in the interstices of the body, it be granted that a diamagnetic 

 may be produced from a magnetic cube in the manner assumed by 

 Professor Tyndall, does it still follow, necessarily, that attraction is 

 always greatest — repulsion least — when the force acts in the line of 

 compression ? In other words, can a conclusion contradictory to 

 experimental facts be then legitimately deduced ? 



In attempting a reply to this question, it will, perhaps, be best to 

 employ the following symbols. Let W represent the attracting 

 force of the magnet upon the medium displaced by the cube and its 

 contents. The value of W will, of course, be unaltered, no matter 

 whether the force acts in, or at right angles to the line of compres- 

 sion. When the force acts in the line of compression, let Pj repre- 

 sent the attracting force upon the particles, Wj the attracting force 

 upon the internal medium, and let Fj be proportional to the resultant 

 attraction of the cubical mass towards the magnet. Let Pj, W., 

 and Fj have similar significations when the force acts at right angles 

 to the line of compression. Then we may put 



Fi=Pi-}-Mi-W, 



F2=P2 + M2-W. 

 Now, in a compressed magnetic cube, experiment proves that 



Fi^F,,, 



or Pi + Mi>Pe+M2, 



i.e. P1-P2 >-(Mi-M„). 



As long as we are ignorant of the properties of the medium within 

 the body, we will, for the sake of completeness, consider the follow- 

 ing three distinct cases. 



I. The attracting force upon the medium within the cube is the 

 same when the force acts in either the one or the other of the two 

 directions, with respect to the line of compression. Here 



M,=M2, 

 hence Pj ^-Pj. 



II. In whichever of the two directions of the force the attraction 

 of the particles may be greatest, the attraction of the internal me- 

 dium is also greatest in the same direction. Here, according as Pj 

 is greater or less than P^, Mj is greater or less than Mj ; hence, 

 inasmuch as 



Pi + M,>P„-fM^, 

 Pi>P2 and Mi>M2. 



III. In whichever of the two directions of the force the attraction 

 of the particles may be greatest, the attraction of the internal me- 

 dium is greatest in the direction perpendicular to the same. Here, 



