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 _Mainland_? in hotter or colder weather? whether in {155} high Winds or Calms? whether in wet weather or dry? whether most when a North, or when a South, when an East or a West wind blows? and whether it keeps the same seasons of Changes? and whether the seasons and changes of the Air and Weather can be thereby discover'd, and the now hidden causes of many other _Phaenomena_ detected? The said _Doctor_ is so much pleased with the discovery already made by the help of this Instrument, that he thinks it to be one of the most wonderful that ever was in the World, if we speak of strangeness, and just wonder, and of Philosophical importance, separate from the interest of lucre. For (_saith he in one of his Letters_) who could ever expect, that we men should find an Art, to weigh all the Air that hangs over our heads, in all the changes of it, and, as it were, to weigh, and to distinguish by weight, the Winds and the Clouds? Or, who did believe, that by palpable evidence we should be able to prove, the _serenest_ Air to be most heavy, and the _thickest_ Air, and when darkest Clouds hang neerest to us, ready to dissolve, or dropping, _then_ to be lightest. And though (_so he goes on_) we cannot yet reach to all the Uses and Applications of it, yet we should be entertain'd for a while, by the truly Honourable Mr. _Boyle_, as the leading person herein, upon the delight and wonder. The _Magnet_ was known many hundreds of years before it was applied to find out _New Worlds_. To me (_saith he_) tis a wonderful delight, that I have alwaies in my Study before my eye such a _Curious Ballance_.