the earth, then at a greater distance from it; the ancients figured to themselves an endless number of circles intersecting each other, by which they endeavoured to understand the great variety of movements. The confusion, however, caused by such an infinity of circles was so perplexing that, at the time no better system was known, one of the kings of Castile,[8] a profound mathematician, was daring enough to say, that if the supreme Being had consulted him when he created the world, he would have given him some good advice. We are filled with horror at the impiety of this expression, but it serves to shew us how absurd must have been the hypothesis which could prompt it. The advice this man wished to have given, undoubtedly regarded the suppression of so many circles, which did but prevent the planetary motions from being understood. Probably he would likewise have expunged from the system two or three superfluous firmaments, supposed to be above the fixed stars. The philosophers, to explain some particular motion of the heavenly bodies, placed, beyond the heaven that bounds our view, a sky of crystal, which communicated this motion to the lower sky. Was a new movement discovered? they had nothing to do but to form a second crystal firmament. In short skies of crystal were made without any trouble. Why did they always chuse crystal? enquired the Marchioness; would nothing else have answered the purpose as well? No, answered I, it was necessary to have a substance, at once transparent and solid, for it was Aristotle's opinion that solidity was essential to the dignity of their nature, and as this was believed by a great man, nobody thought of doubting it. But since that time comets have been seen which, being higher than was formerly imagined, must have broken all the crystal of these skies, in passing through them, and by that mean, thrown the universe into confusion; it was therefore found necessary to change the matter of which these firmaments were composed, into a fluid, such as air. [Footnote 8: Alphonsus, king of Castile died in 1284.]