PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
5 
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 com- 
pressed ; such an idea, however, appears scarcely less tenable than another whicii 
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 
mediate-, the molecular forces are exerted in placing the particles in position, 
and the subsequent phenomena, 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*. 
The foregoing introductory statement will, perhaps, sufficiently indicate the pre- 
sent aspect of this question. The object I proposed to myself in commencing the 
inquiry now laid before the Royal Society, is to obtain, if possible, clearer notions of 
the nature of the diamagnetic force than those now prevalent ; for though, in the pre- 
ceding paragraphs, we have touched upon some of the most complex phenomena of 
magnetism and diamagnetism, and are able to produce these phenomena at will, the 
greatest diversity of opinion still prevails as to the real relationship of the two forces. 
The magnetic force, we know, embraces both attraction and repulsion, thus exhibit- 
ing that wonderful dual action which we are accustomed to denote by the term pola- 
rity. Mr. Faraday was the first who proposed the hypothesis that diamagnetic bodies, 
operated on by magnetic forces, possess a polarity “ the same in kind as, but the re- 
verse in direction, of that acquired by iron, nickel, and ordinary magnetic bodies 
under the same circumstances -f'.” M. W. Weber sought to confirm this hypothesis 
by a series of experiments, wherein the excitement of the supposed diamagnetic pola- 
rity was applied to the generation of induced currents — apparently with perfect suc- 
cess. Mr. Faraday afterwards showed, and his results were confirmed by M. Verdet, 
that effects similar to those described by the distinguished German, were to be attri- 
buted, not to the excitement of diamagnetic polarity, but to the generation of ordinary 
induced currents in the metallic mass. On the question of polarity Mr. Faraday’s re- 
sults were negative, and he therefore, with philosophic caution, holds himself unpledged 
to his early opinion. M. Weber, however, still retains his belief in the reverse polarity 
of diamagnetic bodies, whereas Weber’s countryman M. von Feilitsch, in a series of 
memoirs recently published in Poggendorff’s Annalen, contends that the polarity of 
* The influence of molecular aggregation probably manifests itself on a grand scale in nature. The Snow- 
don range of mountains, for example, is principally composed of slate rock, whose line of strike is nearly north 
and south. The magnetic properties of this rock I And, by some preliminary experiments, to be very different 
along the cleavage from what they are across it. I cannot help thinking that these vast masses, in their pre- 
sent position, must exert a different action on the magnetic needle from that which would be exerted if the 
line of strike were east and west. 
f Experimental Researches, 2429, 2430. 
