Page:1888 Cicero's Tusculan Disputations.djvu/279

 which measure their journey from east to west by immutable stages, never in the least varying from their usual course, while the other completes a double revolution with an equally constant regularity; from each of these facts we demonstrate the volubility of the world (which could not possibly take place in any but a globular form) and the circular orbits of the stars. And first of all the sun, which has the chief rank among all the stars, is moved in such a manner that it fills the whole earth with its light, and illuminates alternately one part of the earth, while it leaves the other in darkness. The shadow of the earth interposing causes night; and the intervals of night are equal to those of day. And it is the regular approaches and retreats of the sun from which arise the regulated degrees of cold and heat. His annual circuit is in three hundred and sixty-five days, and nearly six hours more. At one time he bends his course to the north, at another to the south, and thus produces summer and winter, with the other two seasons, one of which succeeds the decline of winter, and the other that of summer. And so to these four changes of the seasons we attribute the origin and cause of all the productions both of sea and land. The moon completes the same course every month which the sun does in a year. The nearer she approaches to the sun, the dimmer light does she yield, and when most remote from it she shines with the fullest brilliancy; nor are her figure and form only changed in her wane, but her situation likewise, which is sometimes in the north and sometimes in the south. By this course she has a sort of summer and winter solstices; and by her influence she contributes to the nourishment and increase of