370 Mr. S. T. Preston on some Dynamical Conditions 



many mechanical beauties and extreme simplicity as a means 

 to an end, satisfactory, not only in the absence of any other 

 conceivable cause, but as affording a perfectly rational con- 

 ception to the mind of the processes by which the effects are 

 brought about. 



12. The most difficult thing perhaps at first sight is to con- 

 ceive the great ^permeability or porosity of matter necessary 

 to this theory. It may be perhaps just noted in passing, that 

 most truths are strange at first sight, or else it v/ould be com- 

 petent for any one to arrive at them. I think it may be shown 

 that this open structure of matter is a thing in itself probable, 

 and also distinctly warranted on independent grounds. In 

 architectural and engineering structure generally we do not ob- 

 serve a solid block formation, if I may so express it, but that 

 oj^en structure which is essential to elasticity and strength. 

 So in molecular architecture, we may not expect to find a 

 mass a solid block, but of open structure, though we naturally 

 cannot see the interstices. Again, the perfectly free passage 

 of light or the waves of aether through a piece of glass, or a 

 wave of obscure heat through a block of rock-salt, also of the 

 magnetic disturbance through all matter, would by itself prove 

 the extremely open structure of matter. There is therefore 

 no difficulty in admitting the openness of structure of matter 

 essential to the dynamical theory of gravitation, as this is in 

 itself a natural thing, pointed to by other facts*. 



13. The next difficulty is one pointed out by Professor 

 Maxwell in a notice of Le Sage's theory {Encycl. Brit. 1875, 

 page 46, under the word ''Atom "). The argument there is 

 that, in view of the demonstrated fact that particles of matter 

 in collision with each other tend to acquire the same kinetic 

 energy, therefore the kinetic energy of a molecule of ordi- 

 nary matter would ultimately tend to become equal to that 

 of a gravific particle, and that therefore it would appear that 

 the continual impacts of the particles of the gravific medium 

 would necessarily raise matter to an enormous temperature, 

 as the velocity of the gravific particles must of necessity be 

 assumed extremely high. This objection would seem to have 

 considerable weight : but I think it admits of being sur- 

 mounted on taking certain facts into consideration. It will 

 be admitted that, in order to produce gravity, it is only neces- 



* It may be observed that since, by the rejection of the theory of 

 "action at a distance," «/^ motions developed in matter must inevitably 

 he referred to external media, so therefore, in order that matter may be 

 worked (so to express it) by external media, it must have an open struc- 

 ture — as, in analogy, a steam-engine must have an internal open structuie 

 in order that the steam may get at the worliing parts. 



