the Absurdity of Diamagnetic Polarity. 271 



to the left; and let us imagine, for the sake of simplicity, 

 that the magnetic force within the body B is everywhere 

 parallel to the axis of x, so that as we travel parallel to Ox in 

 the positive direction, the force diminishes numerically, whether 

 it be the positive or the negative pole of the permanent 

 magnet which acts on B. Then if we consider a parallelopiped 

 on the base dy dz, the force acting on it parallel to Ox will 



be 



or 



1 -j — ax, 

 dx 



or 



dy dz | ; 



k b dy dz I F -j- dx, 

 CdF 2 



dydz\—dx, 



which is always negative, since F 2 diminishes as 

 and k b is positive. Hence the soft body B is always attracted 

 by the permanent magnet. The same result would have been 

 obtained if B had been air or a gas contained in a bag. 



If the body B be immersed in air or in a gas, or in a soft 

 liquid, the pressures on the two ends of the small parallelo- 

 piped will, by equations (7) and (7'), give a force in the 

 opposite direction to Ox of 



r 



\k a dydz \ 



d¥\ 



dx~ d *> 



where F has the same meaning as before. 



Hence if k b be greater than k a , or the body B more mag- 

 netic than the gaseous or liquid . medium by which it is 

 surrounded, the attraction of the permanent magnet will over- 

 power the pressure on the surface and the body B will be 

 drawn towards the pole of the magnet ; but if k b be less than 

 k a , or B less magnetic than the surrounding medium, the 

 attraction of the permanent magnet will be overpowered by 

 the pressure on the surface, and the body B will appear to be 

 repelled by the permanent magnet. 



We may now sum up the analogies we have found be- 

 tween magnetism and gravitation in the case of homogeneous 

 bodies. First of all, every soft substance is attracted when 

 placed near one pole of a magnet ; and every body is 

 attracted to the earth. Secondly, if a number of soft 

 bodies be magnetized by a steel magnet, we may neglect 



