In the next century the fact, that the diameter of the earth's orbit round the sum is 220 diameters of the sun, is, so far as we know, mentioned for the first time—a statement which implies a true knowledge of the earth's magnitude. This statement is to be found in Galileo's "System of the World," the work which was condemned by the Inquisitors, and for the publication of which he was arraigned, and prohibited from continuing his astronomical researches, or at least from publishing them. The passage in which the measurement of the sun's distance is given, is such as to make it doubtful if the calculation were made at that time. The context is as follows :—"I suppose with the said Copernicus, and also with his opposers, that the semi-diameter of the grand orb, which is the distance of the earth from the sun, containeth 1,208 semi-diameters of the said earth. Secondly, I premise with the allowance aforesaid, and of truth, that the apparent diameter of the sun, in its mean distance, to be about half a degree, that is 30 min. prim., which are 1,800 seconds, that is, 108,000 thirds. And because the apparent diameter of a fixed star of the first magnitude is no more than 5 seconds, that is, 300 thirds, and the diameter of a fixed star of the sixth magnitude, 50 thirds (and herein is the greatest error of the anti-Copernicans), therefore the diameter of the sun containeth the diameter of a fixed star of the sixth magnitude 2,160 times.…
"The diameter of the sun is 11 semidiameters of the earth, and the diameter of the grand orb contains 2,146 of these same semi-diameters, by the assent of both parties; so that, the diameter of the said orb contains the sun's diameter 220 times very near. And because the spheres are to one another as the cubes of their diameters, let us make the cube of 220, which
