HAVING finished the questions concerning the system, we must proceed to those concerning the substance of the heavenly bodies. For the inquiry concerning the substance of the heavenly bodies, and the causes of their motion, belongs principally to philosophy; the inquiry concerning the motion itself and the accidents thereof, to astronomy; the inquiry concerning their influence and power, to both. Now it ought to have been so arranged between astronomy and philosophy, that astronomy should prefer those hypotheses which are most convenient for compendious calculations'; philosophy those which come nearest to the truth of nature. And further, that while the hypotheses adopted by astronomy for convenience should by no means prejudice the truth of the thing, the judgments of philosophy in 'their turn should be such as are perfectly reconcileable with the phenomena of astronomy. But now it comes to pass, contrariwise, that the ,fictions of astronomy have been introduced into philosophy and corrupted it ; while the speculations of philosophers about the celestial bodies please none but themselves, and almost forsake astronomy, looking at the celestial regions in general, but not at all addressing themselves to particular phenomena and their causes. Therefore since both sciences (as now practised) are slight and superficial, we must plant our footing deeper; and treat these two, which by reason of the narrowness of men's views and the practice of professors have been for so many ages separated, as one and the same thing, and making up together one body of science. The first question proposed therefore is, whether the substance of the heavenly bodies is different in kind from the substance of those below? For Aristotle's temerity and cavilling has begotten for us a fantastic heaven, composed of a fifth essence, free from change, and free likewise from heat 1. Now to say nothing at present about the four elements, which this fifth essence sup-

12 Patricius, from whom much of the latter part of the present tract is taken. was born at Cherso in I529. and died in I597. He wrote a treatise on philosophy-Nova de Universis PhilosoPhia-[whic.h was published in I59I]. It is an attempt, of no great value, to conciliate Plato and Aristotle. In the last book, entitled Pancosmia. there is some interesting information touching theories of the tides.