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the Observations of Mr. Hook made in February and March last, and by him communicated to the Royal Society, and since Printed in the Transactions, published Apr. 2. 1666. consonant to the like observations of Jupiter, made by him in May. 1664, and since communicated to the same Society; and then published in the Transactions, of March. 6. then next following. Now that the Earth hath such a motion about its own Axis (whereby it might be fitted to carry about the Moon) is evident by its Diurnal motion. And it seems as evident that the Moon hath not; because of the same side of the Moon alwaies turned towards us; which could not be, if the Moon carried the Earth about: Unlesse we should say, that it carries about the Earth in just the same Period, in which it turnes upon its own Axis: Which is contrary to that of the Sun carrying about the Planets; the shortest of whose Periods, is yet longer than that of the Suns moving about its own Axis. And the like of Jupiter, shorter than the Period of any of his Satellites; if at least the Period of his conversion about his Axis, lately said to be observed, prove trae. (Of Saturn we have not yet any Period assigned; but it's likely to be shorter, than that of his Satelles.) And therefore we have reason to believe, not that by the Moons motion about its Axis the Earth should be carried by a contemporary Period (whereby the same face of the Moon should be ever towards us;) but that by the Earths revolution abouts its Axis in 14. hours, the Moon should be carried about it in about 29. dayes, without any motion on its own Axis: And accordingly, that the Secondary Planets about Jupiter and Saturn, are not (like their Principals) turned about their own Axis. And therefore I am not at all inclined to believe, that the Menstrual Period of the Tides with us, is to be salved by such an Hypothesis.
Instead of this, that Surmise of mine, for I dare not yet, with confidence give it any better name,) of what I have spoken to you heretofore, (and which hath occasioned this present account which I am now giving you,) is to this purpose.
The Earth and Moon being known to be Bodies of so great connexion (whether by any Magnetick, or what other Tye, I will not determine; nor need I, as to this purpose;) as that
