Mr. S. T. Preston on the Kinetic Theory of Gravitation. 305 



10. Just as increase of vibrating energy (temperature) 

 tends, by the increase of pressure thus produced in the inter- 

 vening film of the medium, to dissociate molecules, so reduc- 

 tion of vibrating energy (attendant on reduction of tempera- 

 ture) tends to facilitate the approach of molecules, on account 

 of the reduction of the pressure or repulsive action of the 

 intervening film. Thus the molecules of a vapour when their 

 vibrating energy is reduced (by a fall of temperature) may by 

 the simple momentum of their own encounters, carry them- 

 selves over the neutral point, and thus effect the condensation 

 of the vapour. Numerous other cases might be cited illustra- 

 tive of the application of the above principles, as, indeed, the 

 molecular effects are very similar in their fundamental aspects. 

 The molecular phenomena, however diverse, may be all corre- 

 lated in one fundamental respect, viz. as consisting in phe- 

 nomena of approach and recession. The fundamental condi- 

 tions to be explained, therefore, are the conditions capable of 

 producing the approach and recession of molecules. Whatever 

 may be said of the above deductions, it is at least so far certain 

 that the conditions investigated, and based upon experimental 

 facts, are competent to produce these fundamental movements 

 of approach and recession in the case of molecules, and to do 

 so in the simplest manner, the constitution of media according 

 to the kinetic theory being admittedly the simplest conceivable. 

 To look therefore to other conditions than the simplest would 

 be to imply that the same results are brought about by a 

 superfluity of mechanism. This superfluity is known not to 

 be the characteristic of nature ; and all the teaching of 

 mechanism points to the fact that superfluity or unnecessary 

 complication entirely prevents the attainment of precision and 

 certainty in the mechanical effects. The great precision and 

 unfailing certainty of the molecular effects would therefore 

 render it necessary to infer that the regulating mechanism was 

 simple, or that there was no unnecessary superfluity. 



11. The fundamental conclusion above drawn regarding 

 the mechanism concerned in the approach of molecules is 

 grounded upon the only explanation of the mechanism of 

 gravity that has withstood criticism and received support by 

 competent judges, viz. the kinetic theory of gravity, of which 

 Le Sage's ingenious idea forms the fundamental basis, and is 

 at once the simplest explanation of gravity conceivable. The 



of molecules, was there wrongly stated, the error haying arisen from a 

 seeming analogy between the approach of bodies to masses (tuning-forks 

 &c.) vibrating in air — in the absence of the knowledge recently acquired 

 of the repulsion of gaseous layers. Much of the main principles of the 

 book, however, remain as they were — to be supplemented by the investi- 

 gations contained in the present papers. 



~ Phil. Mag. S. 5. Vol. 5. No. 31. April 1878. X 



