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curious and nice distinguishing of which small changes, Mr. Hook in the Preface to his Micrography, has described such an Instrument with a Wheel, contrived by himself, and, by these two last years trials of it, constantly found most exact for that purpose: which being so accurate, and not difficult to be made, it were desirable, that those who have a Genius and opportunities of making Observations of this kind, would furnish themselves with such of these Instruments, as were exactly made and adjusted according to the Method, delivered in the newly mentioned place.
To say something of the Observations, made by this Instrument, and withal to excite studious Naturalists to a sedulous prosecution of the same, the Reader may first take notice, that the lately named Mr. Boyle hath (as himself not long since did intimate to the Author of these Tracts) already made divers Observations of this kind in the year 1659. and 1660. before any others were publick, or by him so much as heard of; though he has hitherto forborn to divulge them, because of some other Papers (in whose Company they were to appear) which being hindred by other studies and employments, he hath not as yet finished.
Next, that, besides several others, who, since have had the curiosity of making such observations, the Worthy and Inquisitive Dr. John Beal, is doing his part with much assiduity (of which he hath by several Letters acquainted his Friends in London) both by observing himself, and by procuring many Correspondents in several places in England for the same purpose; judging it of great importance, that Observations of this kind be made in parts somewhat distant from one another, that so from many of those, accurately made and then compared, it may be discovered, whether the Aire gravitates more in the parts of the Earth lying more East or West, North or South? whether on such as lie neerer to the Sea, or further up into the Main land? in hotter or colder weather? whether in
