254 KINETIC THEORIES OF GRAVITATION. 



there is one resultant alone v.liicli never by any accident incurs a com- 

 position or experiences a commutation, the constant and unchangeable 

 undulation of gravitation. 



Glennie. 18G1. 



Mr. J. S. Stuart Glennie, in 1861, published in the Philosophical Mag- 

 azine several papers on the subject of gravitation, in which he proposed 

 to show that universal repulsion m the true explanation of this force ; 

 thus referring it rather to a static than a kinetic condition of pressure. 

 In an essay " On the Principles of the Science of Motion," he sets out 

 with the design *' in this attempt to found a general theory, cleared of 

 ceihers and fluids, of properties and virtues." Commencing with the 

 generalization that " a mechanical force, or the cause of a mechanical 

 motion, we know to be in general the condition of a difference of press- 

 ure," he infers, "hence it appears that if a general mechanical theory is 

 possible, the ultimate property of matter must be conceived to be a 

 mutual repulsion of its parts, and the indubitable Newtonian law of 

 universal attraction be deduced herefrom, under the actual conditions 

 of the world. The general experimental condition of the fitness of the 

 mechanical conception of pressure as the basis of a general physical 



and chemical theory evidently is that there be a plenum 



To give distinctness to this idea of the parts of jnatter as mutually re- 

 pulsive, a molecule, or a body (an aggregate of molecules), is conceived 

 as a center of lines of pressure; the lengths and curves of these lines 

 are determined by the relative pressure of the lines they meet; and 

 lines from greater are made up of lesser molecules and their lines, and 

 so on ad infinitum. In speaking of a molecule or body as such a center 

 of pressure, it will be convenient to have a technical name, llather 



than coin a new term, it is proposed to use 'atom' in this sense 



Atoms, or mutually determining centers of lines of pressure, may also 

 be defined and their relations analytically investigated, as mutually de- 

 termining elastic systems with centers of resistance. This is the fun- 

 damental conception (not hypothesis) of the theory Now 



in a system of atoms as above defined, let the centers be of equal mass 

 and at equal distances; there will be no difference of pressure on any 

 one center, no moving force will be developed, and the conditions of 

 equilibrium will be satisfied. But it is clear that forces will be devel- 

 oped, or the general conditions of motion be fulfilled, cither (1) by a 

 difference in the masses of the centers, or (2) by a difference in the dis- 

 tances of the centers, in consequence of a displacement of any one of 

 them, or (3) supposing a state of dynamic equilibrium established in 

 ihe system by its being brought in contact with another system in a 



different state of such equilibrium "' 



'-'■ If all the masses of the system were equal, and all at the same dis- 

 tance from each other, their mutual repulsions would be equal in 'all 

 directions, and they would remain at rest. But if, though two masses 



