I looked at these, lost in wonder. As soon as I had recovered myself I said, "What is this sound, so great and so sweet, which fills my ears?"--"This," he replied, "is that music which, composed of intervals unequal, but divided proportionately by rule, is caused by the swing and movement of the spheres themselves, and by the proper combination of acute tones with grave, creates with uniformity manifold and diverse harmonies. For movements so mighty cannot be accomplished in silence; and it is a law of nature that the farthest sphere on the one side gives forth a base tone, the farthest on the other a treble; for which reason the revolution of that uppermost arch of the heaven, the starry firmament, whose motion is more rapid, is attended with an acute and high sound; while that of the lowest, or lunar arch, is attended with a very deep and grave sound. For the ninth sphere, the earth, embracing the middle region of the universe, stays immovably in one fixed place. But those eight globes between, two[A] of which have the same essential action, produce tones, distinguished by intervals, to the number of seven; which number indeed is the knot of almost all things. Men of skill, by imitating the result on the strings of the lyre, or by means of the human voice, have laid open for themselves a way of return to this place, just as other men of lofty souls have done the same by devoting themselves during their earthly life to the study of what is divine. But the ears of men, surfeited by this harmony have become deaf to it; nor is there in you any duller sense: just as, at that cataract which is called Catadupa,--where the Nile rushes down headlong from the lofty mountain-tops,--the people who dwell in that neighborhood have lost the sense of hearing in consequence of the magnitude of the sound. So likewise this harmony, produced by the excessively rapid revolution of the whole universe, is so great that the ears of men are not able to take it in, in the same manner as you are not able to look the sun in the eye, and your sight is overcome by the power of its rays." Though I was filled with wonder, nevertheless I kept turning my eyes from time to time to the earth. [A] Mercury and Venus.