Bodies are 7-epelled from the Poles of a Magnet. 157 



molecular arrangement of a body be changed, such a change 

 will manifest itself by an alteration of deportment towards any 

 force operating upon the body : the action of compressed glass 

 upon light, which Wertheim in his recent researches* has so 

 beautifully turned to account in the estimation of pressures, is 

 an illustration in point; and the inference also receives the 

 fullest cqfroboration from experiments, some of which are re- 

 corded in the papers alluded to, and which show that all the 

 phsenomena of magnecrystallic action may be produced by simple 

 mechanical agency. What the crystalline forces do in one case, 

 mechanical force, under the control of the human will, accom- 

 plishes in the other. A crystal of carbonate of iron, for example, 

 suspended in the magnetic field, exhibits a certain deportment : 

 the crystal may be removed, pounded into the finest dust, and 

 the particles so put together that the mass shall exhibit the 

 same deportment as before. A bismuth crystal suspended in 

 the magnetic field, with its planes of principal cleavage vertical, 

 will set those planes equatorial ; but if the crystalline planes 

 be squeezed sufficiently together by a suitable mechanical force, 

 this deportment is quite changed, and the line which formerly 

 set equatorial now sets axialt- 



Thus we find that the influence of crystallization may be 

 perfectly imitated, and even overcome, by simple mechanical 

 agencies. It would of course be perfectly unintelligible were 

 we to speak of any direct action of the magnetic force upon the 

 force by which the powdered carbonate of iron, or the solid cube 

 of bismuth, is compressed ; such an idea, however, appears 

 scarcely less tenable than another which seems to be entertained 

 by some who feel an interest in this subject ; namely, that there 

 is a direct action of the magnet upon the molecular forces which 

 built the crystal. The function of such forces, as regards the 

 production of the effects, is, I believe, mediate; the molecular 

 forces are exerted in placing the particles in position, and the 

 subsequent phfenomena, whether exhibited in magnecrystallic 

 action, in the bifurcation and polarization of a luminous ray, 

 or in the modification of any other force transmitted through 

 the crystal, are not due to the action of force upon force, except 

 through the intermediation of the particles referred to J. 



* Phil. Mag. October and November 1854. 



t Phil. Mag. vol. ii. Ser. 4. p. IH.'J. 



X The iuilueucc of molecular aggregation probably manifests itself on a 

 grand scale ia nature. The Snowdou range of mountains, for examjile, 

 IS principally composed of slate rock, whose line of strike is nearly north 

 and south. The magnetic jjroperties of this rock I find, by some prelimi- 

 nary experiments, to be very diflerent along the cleavage from what they 

 are across it. I cannot help thinking that these vast masses, in their 

 present j)Osition, must exert a dilferent action on the magnetic needle 

 from that which would be exerted if the line of strike \vere east and west. 



