Page:Popular Astronomy - Airy - 1881.djvu/93

Rh written a whole "book on the motion of a top, and his Latin Treatise "De motu Turbinis" is one of the most remarkable books on mechanics, I ever read in my life. The motion of a top, I repeat, is a matter of the greatest importance; it is applicable to the elucidation of some of the greatest phenomena of nature. In all these instances there is this wonderful tendency in rotation to preserve the axis of rotation unaltered.

Now, from all these circumstances, we see sufficient reason to explain how, whilst the earth is going round the sun, its axis of rotation should remain parallel to itself without being disturbed, that is to say, that the position of the axis has no respect whatever to the sun. Whatever the position of the axis of rotation be, the earth will travel through space keeping that axis of rotation in the same position with regard to the distant stars. Having reached this very important point in the science, I will stop for the present.