32 Proceedings of Royal Society of Edinburgh. [sess. 
what we will — adopt what hypothesis we please — there is no 
escape, in dealing with the phenomena of light, from these gigantic 
numbers, or from the conception of enormous physical force in per- 
petual exertion at every point , through all the immensity of space 
.... Every phenomenon of light points strongly to the con- 
ception of a solid rather than a fluid constitution of the luminif- 
erous ether, in this sense— that none of its elementary molecules 
are to be supposed capable of interchanging places , or bodily trans- 
fer to any measurable distance from their own special and assigned 
localities in the universe.” This is the famous ‘jelly’ constitu- 
tion of the ether, which has been much ridiculed, but never yet 
confuted. The only argument of any weight against it is the 
difficulty of conceiving how solid, massive bodies like the planets 
can trace out their orbits, time after time, with unvarying regular- 
ity through it, without showing the slightest sign of retardation. 
Well, now, I think if I can rid the theory of this particular 
stumbling-block — and I think I may promise my readers that I 
can — it ought to be considered once more as within the bounds of 
the possible. Futhermore, I may help to greatly strengthen it by 
pointing out the possible — nay, probable — source of the intense 
pressure which Herschel found must exist in the medium. 
When we look abroad on a clear, dark night, we find the sky 
-studded with sparkling points of light in every direction ; and if 
we use a telescope, it is found that the higher its powers the more 
-closely set do these points of light become, until it is difficult to 
resist the conclusion that the bodies which emit the light are 
existing in every direction in space, and that the reason the sky 
does not show up as one square sun, as it were, is that a great deal 
of the light may be absorbed, or change its character on its 
practically infinite journey towards us; in short, that the uni- 
verse of stars is practically infinite. Now, it is practically 
certain that all those stars are suns ; suns, some of them far 
larger, and some no doubt smaller, than our own sun, each 
emitting light and heat, generally, comparable with the sun. Now, 
what becomes of this light and heat? Is it wasted? No; the 
principle of the conservation of energy forbids that it should be 
wasted. What, then, becomes of it? Let us consider. If the 
ether is formed of discrete particles — and I think it is impossible 
