On the Radiometer, the Otheoscope, and the Telephone. 453 

 for a factor the square of the harmonic function m sin (a£ + c), 



771 w Yll 



or -5 ^ cos 2(a£ + c). The pressure on the atom is conse- 



quently partly such as a current corresponding to the indica- 

 tion of the first term would produce, and partly such vibratory 

 motion as would be due to the pressure indicated by the second 

 term. The former gives rise to motion of translation of the 

 atom, and to acceleration of such motion. The acceleration 

 may either be from or towards the source of the vibrations, 

 according to the relation between the magnitude of the atom, 

 and the breadth and intensity of the waves. The waves which 

 emanate from individual atoms by reason of reaction from their 

 surfaces, are all of such small magnitude that they act in the di- 

 rections from the centres of the atoms on all surrounding atoms. 

 This force is atomic repulsion. The composite waves resulting 

 from the coexistence of those emanating from a vast number 

 of atoms constituting a molecule may be supposed of such mag- 

 nitude and breadth as to be capable of producing acceleration 

 of exterior atoms in the direction toivards the centre of the 

 molecule. This is molecular attraction. The equilibration of 

 the two kinds of forces maintains the aggregation of atoms 

 which constitutes visible and tangible bodies. The arguments 

 on which these statements are based are given in the article in 

 the Philosophical Magazine for September 1872, already cited, 

 and in a " Supplementary Discussion of the Hydrodynamical 

 Theory of Attractive and Repulsive Forces," contained in the 

 Number for September 1876. The statements are introduced 

 here for the purpose of making intelligible the following 

 General Theorems, to which the investigations referred to 

 conduct : — 



I. Assuming that the repulsive and attractive forces of nature 

 are all resultants of modes of pressure of the aether, the actions 

 of such forces on atoms are in every instance attributable to 

 cethereal currents, whether the atoms be immediately acted upon 

 by steady motions of the aether or by aethereal vibrations. 



II. In any instance in which a gradation of atomic density 

 exists in the interior of any body, in so far as this condition is 

 persistent, molecular attraction in the direction from rarer to 

 denser parts must be counteracted by atomic repulsion in the 

 contrary direction ; and according to theorem I. these actions 

 are accompanied by aethereal currents. 



In the case in which an atom in the interior of a homoge- 

 neous body is kept at rest by atomic repulsion and molecular 

 attraction, the resultant of each kind of force is zero, and there 

 is consequently no direct evidence of the action or existence 

 of aethereal currents. But if the atom be near the superficies 



