22 J. MORiSON : ADDRESS 



miles in diameter, and enormous accumulations of nebulous 



material, so vast that it would take light, travelling as it does at 



the rate of 185,000 miles a second, many days, months, or even 



years to traverse them. Let us begin with the Solar System. 



Our Eartli is a globe about 8,000 miles in diameter, for the most 



part solid or practically so from centre to circumference. This 



solid mass is partially surrounded by an envelope of liquid, or 



water, and outside this again we have an envelope of gaseous 



matter forming the atmosphere. We know that the interior of 



the solid globe is in an intensely heated condition, and there is 



eveiy reason to believe that in ages long past the heat of the 



Earth was very much greater than it is now. The planet Venus 



is probably in about the same physical condition as the earth. 



Mars is considerably smaller and contains less water and air in 



proportion to its size, and has probably lost more of its internal 



heat. In the Moon we have a body much smaller still, and 



apparently composed altogether of solid material, there being 



no appreciable watery or gaseous envelope ; and probably it has 



almost entirely parted with its primaeval heat. Most of the other 



satelhtes and the asteroids, bodies still smaller, may be in the 



same physical condition as the Moon. Then we have meteors, 



small pieces of dead cold matter which travel round the Sun in 



very eccentric orbits, and probably enter to some extent into the 



composition of comets. The rings of Saturn are supposed to be 



composed of bodies of this kind. Then we come to the larger 



planets, Jupiter, Saturn, etc., which are very much larger than 



the earth and of much smaller density, and are therefore believed 



to be extremely hot. They are considered to be composed of 



matter in a liqiud state, at any rate for the most part, and they 



are surrounded by very deep and dense gaseous envelopes. Then 



we have the Sun, the centre of our system, 860,000 miles in 



diameter, of enormous size compared to his dependants, and 



believed to be an immense mass of dense and intensely-heated 



matter in a gaseous condition. Thus we have in our system, one 



very large central body which is very highly heated and gaseous 



in constitution ; several smaller bodies which are less heated and 



composed of liquid and gaseous matter ; then still smaller bodies 



wliich are mostly solid with lic^uid and gaseous envelopes 



surrounding them, and which are only heated in their interiors ; 



and finally smaller bodies still, which are entirely solid and qmte 



cold. It is difficult to resist the conclusion that these masses of 



matter were once all in the same condition, all intensely heated 



and gaseous, and that their present differences of constitution and 



