Attractive and Repulsive Forces. 209 



bable that beyond these limits others exist not recognizable by 

 the power of vision. According to the hydrodynamical views I 

 maintain, the special form of the simple vibration and the values 

 of X result spontaneously from a disturbance without being de- 

 termined by the particular character of the disturbance (see 

 arts. 13-15 in the Theory of Magnetism, June Number). Of 

 all orders of vibrations those may be presumed to have the 

 least values of \ which emanate from individual atoms, and are 

 due to the aggregate of reactions at their surfaces consequent 

 upon the incidence of vibrations from aJl surrounding quarters. 

 According to a foregoing argument (art. 32), it may be assumed 

 that, for undulations of this order incident on an atom, H will be 

 a negative quantity, and consequently that any given atom is 

 always repulsive towards surrounding atoms. This is the theory 

 of the force I call atomic repulsion, which 1 consider to be the 

 same as the repulsion of heat. 



41. The vibrations emanating from a vast number of atoms 

 constituting a molecule may be conceived to produce by their com- 

 position vibrations of another order, in which the characters of 

 the component vibrations are obliterated and the values of \ are 

 much larger. If we may suppose that for vibrations of this 

 order H has a positive value, we shall be able to account for a 

 molecular attraction acting so as to control at the boundaries of 

 substances the atomic repulsion, and thus have the effect of 

 maintaining the atoms, both superficial and interior, in positions 

 of equilibrium. Assuming that H may have both a negative 

 and a positive value, we might infer that for certain values of \ 

 that quantity either vanishes or is very small. Possibly these 

 may be the values for light-undulations, which seem to possess 

 vibratory rather than translatory power. The whole theory, 

 however, of attractive and repulsive forces, regarded as due to 

 vibrations of the osther, is incomplete for want of an a priori de- 

 termination of the composition and value of the quantity H. 



42. The composite class of vibrations to which the theory 

 ascribes molecular attraction must, by the mere effect of separa- 

 tion caused by propagation to a great distance, be resolved into 

 the component primitive vibrations, which will again act repul- 

 sively, and require to be controlled by another order of attrac- 

 tion-vibrations, and so on till we come to the attraction-vibra 

 tioDs of gravity. Moreover, as it is impossible to account for the 

 stability of the general system of stars, or of systems of stars 

 which constitute resolved nebulps, if the individuals simply 

 attract each other by the force of gravity, it seems reasonable 

 to suppose that the gravity-vibrations may in like manner be re- 

 solved by propagation to vast distances into repulsive- compo- 

 nents. In this manner neighbouring stars would be mutually 

 Phil. Mag. S. 4. Vol. 44. No. 292. Sept. 1872. P 



