454 THE WORLD MACHINE 



with an average equal motion, and so small that they would 

 penetrate and flow through all forms of matter whatsoever. 

 Because this rain must be incessant and to all intents infinite, 

 Lesage conceived it to come from beyond the confines of the 

 known universe ; hence he called these flying bodies ultra- 

 mundane particles. 



It will be perceived that Lesage's idea of an eternal downpour 

 of minute particles of matter does not differ very greatly from 

 the ideas of Democritus and Epicurus. It is evident from his 

 memoir that it was a reading of these which probably suggested 

 the hypothesis he framed. It was, to be sure, a purely specu- 

 lative conception. It was a kind of an explanation ad hoc. 

 Before us is a fact how might it be explained ? We have of 

 course not the ' slightest evidence that any such corpuscular 

 downpour takes place. 



Still, it is noteworthy that Lesage's hypothesis has been 

 favourably entertained by more than one acute and penetrating 

 mind, in especial, that of S. Tolver Preston, an English physical 

 philosopher who gave high promise ere he died. It was Tolver 

 Preston who pointed out that the scheme imagined by Lesage 

 differed but little from our present-day theory of gases, of the 

 cause of the pressure of air, &c. His postulates were much the 

 same. 1 We should merely have to imagine an order of cor- 

 puscles as much smaller let us say, than the molecules or 

 particles of air as the latter are smaller than small shot or sand. 



Very recently in the emanations of radium we have learned 

 to know of a corpuscular order perhaps a thousand times smaller 

 than the smallest of the atoms, possibly hundreds of thousands 

 of times smaller than the molecular aggregations of air or vapour. 

 There is nothing a priori to forbid our imagining that a' yet more 

 minute order exists, and sufficient in numbers to satisfy the 

 assumptions of Lesage as they were modified in the mind of 

 Preston. Probably we are as yet merely upon the rim of physical 

 knowledge. Of what another two or three centuries like the 

 last may bring forth we have of course not the remotest sus- 

 picion. But so far as our present-day knowledge extends, the 

 theory is little more than a brilliant fancy. 



Endeavours at an explanation of a hydro-dynamical sort have 

 not been few. It has been known for a very long time that 

 pulsating spheres, immersed in an incompressible medium like 

 1 Philosophical Magazine, 1878-79. 



