Page:Popular Astronomy - Airy - 1881.djvu/85

Rh rapidly, and whirl it round; then as soon as the motion of rotation takes place, the hoop becomes flattened.

From all these considerations then, put together in proper order, we infer, as a matter of positive certainty (however hard it may be at first for our minds to receive it), we infer as a matter of certainty that it is the earth which revolves.

I shall now proceed with the next subject—the apparent motion of the sun amongst the stars. I make a point of entering upon this subject at the present time, that I may address to you some rough observations for your guidance in the enquiries which this subject involves. I shall explain to you the evidence which is within your own reach, and which proves that the sun apparently moves through the stars. I have not yet specially alluded to the sun in speaking of revolution; my remarks on that point referred only to the stars. I am now, however, going to speak of the sun a little, though it is necessary to have the stars to begin with, as fixed points in the heavens.

Everybody knows the leading difference between summer and winter; we know that the days are longer in the summer than in the winter. If you consider for a moment something else which you know and have remarked, you will see this, that the position of the sun is different in summer from what it is in winter. In summer, the sun at noon-day is high in the heavens; in the winter at noon-day he is