Page:Popular Astronomy - Airy - 1881.djvu/109

Rh the country of Greece," and that he was persecuted for saying so. Having these things before us, I am not much surprised that the Greek astronomers considered the sun as completely subordinate to the earth, and therefore supposed it to revolve round the earth; and when they had once adopted this idea, they were compelled to take the complicated and unnatural explanation which I have given of the motion of the planets.

The motions of the planet Mars, however, still presented some discordance, and there were some smaller discordances with regard to all the other planets. Then were invented those things known by the name of epicycles, deferents, &c. of which the nature may be thus explained. By the contrivance of which I have previously spoken, (and which is represented in figure 26), they found that the movement of the point Ma at the end of the rod n Ma would nearly, but not exactly, represent the motion of Mars. To make it represent the motion more exactly, they supposed that another small rod MN was carried by the longer rod, jointed at M, and turning round in a different time. To make it still more exact, they supposed another shorter rod carried at N, and that its extremity carried the planet Mars; and so for the other planets. Of all the complications of systems that ever man devised, there never was one like this Ptolemaic system. The celebrated King of Castile, Alphonse, the greatest patron of Astronomy in his age, alluding to this theory of epicycles, said "If he had been consulted at the Creation, he could have done the thing better." It was merely expressing his absolute inability to receive, as a possible explanation of nature, such a complexity of things.

But there was one consideration so simple, that it