156 Prof. Tyildall on the Nature of the Force by which 



morphous magnetic constituent^ which neither altered the struc- 

 ture nor affected the perfect transparency of the crystal, the 

 optic axis set itself from pole to pole. The various complex 

 phsenomena exhibited by crystals in the magnetic field were 

 finally referred to the modification of the magnetic and diamag- 

 netic forces by the peculiarities of molecular arrangement. 



This result is in perfect conformity with all that we know 

 experimentally regarding the connexion of matter and force. 

 Indeed it may be safely asserted that every force which makes 

 matter its vehicle of transmission must be influenced by the 

 manner in which the material particles are grouped together. 

 The phfeuomena of double refraction and polarization illustrate 

 the influence of molecular aggregation upon light. Wertheim 

 has shown that the velocity of sound through wood, along the 

 fibre, is about five times its velocity across the fibre : De la Rive, 

 DeCandolle and myself have shown the influence of the same 

 molecular grouping upon the propagation of heat. In the first 

 section of the present paper, the influence of the molecular 

 structure of wood upon its magnetic deportment is described : 

 De Senarmont has shown that the structure of crystals endows 

 them with difl^erent powers of calorific conduction in difi"erent 

 directions : Knoblauch has proved the same to be true, with 

 regard to the transmission of radiant heat : Wiedemann finds the 

 passage of frictional electricity along crystals to be aff'ected by 

 structure ; and some experiments, which I have not yet had 

 time to follow out, seem to prove, that bismuth may, by the 

 approximation of its particles, be caused to exhibit, in a greatly 

 increased degree, those singular effects of induction which are 

 so strikingly exhibited by copper, and other metals of high 

 conducting power. 



Indeed the mere (i j)rio7-i consideration of the subject must 

 render all the effects here referred to extremely probable. Sup- 

 posing the propagation of the forces to depend upon a subtle 

 agent, distinct from matter, it is evident that the progress of 

 such an agent from particle to particle must be influenced by 

 the manner in which these particles are arranged. If the par- 

 ticles be twice as near each other in one direction as in another, 

 it is certain that the agent of which we speak will not pass with 

 the same facility in both directions. Or supposing the effects 

 to which we have alluded to be produced by motion of some 

 kind, it is just as certain that the propagation of this motion 

 must be affected by the manner in which the particles which 

 transmit it are grouped together. Whether, therefore, we take 

 the old hypothesis of imponderables, or the new, and more 

 philosophic one, of modes of motion, the result is still the same. 



If this reasoning be correct, it would follow, that, if the 



