THE ETHER OF SPACE 301 



however, was not my intention. The view I advocate is 

 that the ether is a perfect continuum, an absolute plenum, 

 and that, therefore, no local rarefaction is possible. The 

 ether inside matter is just as dense as the ether outside, 

 and no denser. A material unit say an electron is only 

 a peculiarity or singularity of some kind in the ether itself, 

 which is of perfectly uniform density everywhere. What 

 we sense as matter is an aggregate or grouping of an 

 enormous number of such units. 



How, then, can we say that matter is millions of times 

 rarer or less substantial than the ether of which it is essen- 

 tially composed ? Those who feel any difficulty here should 

 bethink themselves of what they mean by the average or 

 aggregate density of any discontinuous system, such as a 

 powder, or a gas, or a precipitate, or a snowstorm, or a 

 cloud, or a Milky Way. 



Lord Kelvin has estimated and, indeed, proved that the 

 aggregate density of the whole material cosmos within 

 recognizable gravitational reach of us must be infinitesimal ; 

 in other words, that the amount of matter In space, how- 

 ever prodigious it may be, must be infinitely less than the 

 volume of space it occupies. And even of the visible cos- 

 mosthat is to say, of the material clustering within reach 

 of our aided organs of vision the density, though cer- 

 tainly not infinitesimal, is exceedingly small. 



It may be clearer if I give some actual numbers. Lord 

 Kelvin estimates the amount of matter within reach of the 

 largest telescopes say within a parallax of -nnnr second of 

 arc, corresponding to a radius of 3 x 10 16 kilometers as 

 equivalent to a thousand million of our suns ; that is, to a 

 total mass of 1.5 x 10 36 tons distributed through a volume 

 of 1.12 x 10 59 cubic meters. So the density of the visible 

 cosmos comes out of the order of 10 ~ 23 of that of water. 



The masses themselves seem likely to be in the main dis- 

 tinctly of greater density than water; but grouped, or in 

 the aggregate, they are excessively " rare "far rarer than 

 the residual gas in the highest-known vacuum. The whole 



