Prof. Challis on a Theory of the Force of Electricity, 281 



depend only on the magnitudes of their atoms, the proportions in 

 which they are composed of atoms of different magnitudes, and 

 on the arrangements of the atoms. But the explanation of the 

 sensible properties of matter must be preceded by a mathematical 

 investigation of the laws of the dynamic action of the assumed 

 setherial medium. Already I have entered to some extent on 

 such investigations relatively to light, heat, the force of gravity, 

 and the forces of molecular aggregation. I proceed now to treat 

 of the force of electricity on the same principles. First, how- 

 ever, it should be stated, with respect as well to this investiga- 

 tion as to those which preceded it, that I do not profess to give 

 complete and final explanations of the laws of the forces under 

 consideration. As the proposed general theory either embraces 

 all the physical forces, or fails altogether, my object at present 

 is to adduce prima facie evidence that it is as comprehensive as 

 it is required to be. 



1. According to the "Theory of Molecular Forces" contained in 

 the Number of the Philosophical Magazine for last February, 

 the atoms of any substance are kept in positions of equilibrium 

 by attractions and repulsions resulting from the dynamical action 

 of vibrations of the sether, which have their origin at the atoms. 

 Each atom is the centre of vibrations propagated from it equally 

 in all directions, and that part of the velocity of the vibrations 

 which, as shown by the mathematical formula?, is unaccompanied by 

 change of density, gives rise to a repulsive action on the surround- 

 ing atoms, varying inversely as the fourth power of the distance. 

 This action is the calorific repulsion which keeps the individual 

 atoms asunder. The remaining part of the velocity, which is 

 accompanied by a proportional condensation, acts repulsively also, 

 according to the law of the inverse square, but with a force which 

 at the surface of the atom is incomparably less than the other 

 repulsion. When, however, the effect of all the repulsions of 

 the second kind from an aggregation of atoms, constituting a 

 spherical molecule, is considered, the resultant may be of sensible 

 magnitude at sensible distances from the centre of the molecule. 

 To this molecular action the repulsion of aeriform bodies is attri- 

 buted in the theory referred to. It appeared also from the the- 

 oretical investigation, that the separate waves from the atoms of 

 a spherical molecule of a higher order of magnitude, consisting 

 of a number of atoms very much larger than those constituting 

 the molecule of the first order, might merge at a certain distance 

 from its centre into continuous waves of another order of breadth 

 and condensation, the dynamic action of which might be such 

 as to account for the molecular attraction of aggregation in fluids 

 and solids. 



For the sake of distinction, the first of the above-mentioned 

 Phil Mag, S. 4. Vol. 20. No. 133. Oct. 1860. U 



