A Relation of some Mercurial Observations, and their Results.
Modern Philosophers, to avoyd Circumlocutions, call that Instrument, wherein a Cylinder of Quicksilver, of between 28. and 31. Inches in Altitude, is kept suspended after the manner of the Torricellian Experiment, a Barometer or Baroscope, first made publick by that Noble Searcher of Nature, Mr. Boyle, and imployed by Him and others, to detect all the minut variations in the Pressure and weight of the Air. For the more
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 Mainland? in hotter or colder weather? whether in
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 Phænomena 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.
Having thus in General expressed his thoughts about this Invention, and the singular pleasure, he takes in the Observations made therewith, he descends to particulars, and in several Letters communicates them to his Correspondent, as follows:
The Exclusion of all Air is here necessary, because Air being subject to the operation of Heat and Cold, if any of it remain in the Barometer, it will cause it to vary from shewing the true Pressure of the Air.