162. Now, without speculating about the nature or extent of the ethereal medium, we may be sure of two things. In the first place, all but an exceedingly small fraction of the light and heat of the sun and stars goes out into space and does not return to them again, or in other words, the sun and stars are slowly cooling. To restore to the sun every instant its losses by radiation, the whole celestial vault would have to radiate as powerfully as the sun does—in which case the earth and planets would very soon acquire (at their surfaces) the sun’s temperature. In the next place, the visible motion of the large bodies of the universe is gradually being stopped by something which may be denominated ethereal friction. It follows from this that our own sun will gradually lose his brilliancy, and that our earth will gradually lose its orbital energy and approach the sun in a path of slowly contracting spiral convolutions. At last it will become entangled with the sun, and the result will be the conversion of the remaining orbital energy into heat, after which the two bodies will remain one. Thus the tendency is that the sun shall ultimately absorb the various planets of the system, his heat and energy being recruited by the process. Now, let us imagine that the same processes are simultaneously going on in one of the nearer fixed stars, say for instance in Sirius. After unimaginable ages these two stars, the Sun and Sirius, having each long since swallowed up his attendants, but being nevertheless exhausted in heat-energy on account of radiation into space, may be imagined to be travelling towards one another, slowly at first, but afterwards with an accelerated motion. They will at last approach each other with a great velocity, and finally form one system. Ultimately the two will rush together and form one mass, the orbital energy of each (or rather that portion of this energy which remains after ethereal friction) being converted into heat, and the matter being, in consequence, probably partly smashed into mere dust, and partly evaporated and transformed into a gaseous, nebulous condition. Ages pass away, and the large double mass ultimately shares the same fate that long since overtook the single masses which composed it; that is to say, it shrinks and throws off planets, but gives out the greater part of its light and heat into space and gradually becomes cold and dark, until at length it comes to form one of the constituents of a still more stupendous collision, and has its temperature raised once again by the conversion of visible energy into heat.