64 JOURNAL OF SCIENCE. 
sal proportions, give it an elevation and sublimity all its own. Its 
time-periods seem, rather, like hours on the dial-plate of eternity. 
The spaces of its immensity are confounded, practically, with 
infinity itself. 
In view of all this it is remarkable how few people take more 
than a superficial interest in the subject. Even the circles and 
apparent motions of the celestial sphere, simple as they are, and 
ever open to observation, are to most people unknown and unin- 
telligible, The planets are unrecognised. Beyond a knowledge 
of one or two conspicuous constellations—not always certainly or 
steadily known—these “flowers of the sky” have to most no 
more meaning or interest than the “ yellow primrose ” to the soul 
of Peter Bell. It is astonishing how few people accurately know 
even the Southern Cross. Its appearance in any new position 
seems always an occasion of bewilderment. One of the best 
educated men I know was recently trying to point it out to me 
in the constellation of Canzs Majyor—a mistake something like 
looking for illustrations of the anatomy of Invertebrates in the 
body of a barrel-organ ! 
I have spoken of the prevalence of biological study. I have 
ventured to suggest that some of the enthusiasm with which it 
is pursued might be advantageously diverted—raised, in fact, from 
earth to heaven. Yet I am conscious that to put biology in 
antithesis to astronomy, is to do an injustice to, both. The two 
sciences have so close a connection, that the intermediate subject 
of Geology may be said to be common property. The cosmical 
aspects of geology belong to the science of astronomy. Nay 
more. It is remarkable that one of thegreat puzzles of geology— 
the problem of glacial periods—finds its solution in some of the 
great rhythmical movements of the solar system. The point is 
one of so much interest, and is so well fitted to conciliate the 
rival claims of the two lines of study, that Iam tempted to tell 
the whole story. 
The Earth’s orbit, its revolution round the sun, is at present 
nearly circular. Not quite, however, for its ellipticity is such 
that, during our (southern) winter, we are about three million miles 
farther from the sun than during our summer. This slight dif- 
ference of distance does not itself make any sensible difference 
in the temperature between north and south ; but it has an effect 
on the length of the seasons, through one of the great laws of 
orbital motion, and in that way has a quite appreciable effect on 
the temperature. It makes the cold period of the year in the 
southern hemisphere nearly eight days longer than the warm 
period ; and correspondingly, of course, it makes the warm 
period in the northern hemispherenearly eight days longer thanthe 
cold period. And such a difference has a sensible effect on tem- 
perature. It probably accounts for the greater collection of ice 
around the South Pole. In consequence of the precession of 
the equinoxes, this condition is subject to a gradual change, 
which, in the course of about 10,500 years reverses the inequa- 
lities of temperature above described. Ten thousand yearshence , 
