The different periods in which these mutations happen are called by Plato, with great propriety, periods of _fertility_ and _sterility_; for in these periods a fertility or sterility of men, irrational animals, and plants takes place; so that in fertile periods mankind will be both more numerous, and upon the whole superior in mental and bodily endowments, to the men of a barren period. And a similar reasoning must be extended to animals and plants. The so much celebrated heroic age was the result of one of these fertile periods, in which men transcending the herd of mankind both in practical and intellectual virtue abounded on the earth. And a barren period may be considered as having commenced somewhat prior to the Augustan age, the destruction of all the great ancient cities, with all their rites, philosophy, &c. being the natural consequence of such a period. It appears to me that this period commenced in the time of Sylla, and I found this opinion on the following passage in Plutarch’s Life of that great commander:—Το δε παντων μεγιστον, εξ ανεφελου και διαιθρου του περιεχοντος ηχησε φωνη σαλπιγγος, οξυν αποτεινουσα και θρηνωδη φθογγον, ὡστε παντας εκφρονας γενεσθαι, και καταπτηξαι το μεγεθος. Τυρῥηνων δε οἱ λογιοι μεταβολην ἑτερου γενους απεφαινοντο, και μετακοσμησιν αποσημαινειν το τερας. ειναι μεν γαρ αυτῳ οκτω τα συμπαντα γενη διαφεροντα τοις βιοις και τοις ηθεσι δ’ αλληλων, ἑκαστῳ δε αφωρισθαι χρονων αριθμον, ὑπο του θεου συμπεραινομενον ενιαυτου μεγαλου περιοδῳ· και ὁταν αυτη σχη τελος, ἑτερας ενισταμενης κινεισθαι τι σημειον εκ γης ἢ ουρανου θαυμασιον. i. e. “But the greatest of all [the signs prior to the civil wars] was the following: On a cloudless and clear day, the sound of a trumpet was heard, so acute and _mournful_ as to astonish and terrify by its loudness all that heard it. The Tuscan wise men and soothsayers, therefore, declared that this prodigy signified the mutation into and commencement of another age. For according to them there are eight ages, differing from each other in lives and manners, each of which is limited by divinity to a certain time of duration, and the number of years of which this time consists is bounded by the period of the great year. Hence, when one age is finished, and another is about to commence, a certain wonderful sign will present itself, either from the earth or the heavens.” The _mournfulness_ of this sound of the trumpet was evidently an indication that a barren period was about to commence.—For an account of the _great year_, see the note to page 478 of the treatise on Meteors. The following extracts from a work entitled “Sketches chiefly relating to the History, Religion, &c. of the Hindoos, concerning the Mundane Periods,” appear to me to be highly interesting, and to form a most important addition to what has been before said about the revolutions which take place in the universe.