In my _Baroscope_, I have never found the Quicksilver higher than 30. inches, nor lower than 28. (at least, scarce discernably, not 1/16 of an inch higher than _that_, or lower than _this_;) which I mention, not only to shew the limits, within which I have observed mine to keep, _vid._ full 2 inches, but likewise as an Estimate of the Clearness of the Quicksilver from Air. For, though my Quicksilver were with good care cleansed from the Air; yet I find that which Mr. _Boyle_ useth, much better: for, comparing his with mine at the same times, and both in _Oxford_, at no great distance; I find his Quicksilver to stand alwaies somewhat higher than mine (sometimes neer a quarter of an Inch;) which I know now how to give a more probable account off, than that my Quicksilver is either heavier than his; or else, that his is better cleansed from Air, (unless, possibly, the difference of the Bore, or other circumstances of the Tube, may cause the alteration; mine being a taller Tube, and a bigger Bore, than his.) And upon like reason, as his stands higher than mine; so another less cleansed from Air, may at the same time be considerably lower, and consequently under 28. Inches at the lowest. In _thick foggy_ weather, I find my Quicksilver to rise; which I adscribe to the heaviness of the Vapours in the Air. And I have never found it higher, than in the foggy weather above-mentioned. In _Sunshiny_ weather it riseth also (and commonly the clearer, the more;) which, I think, may be imputed _partly_ to the Vapors raised by the Sun, and making the Air heavier; and _partly_ to the Heat, increasing the Elastick or Springy power of the Air. Which latter I the rather add, because I have sometimes observed in Sunshiny weather, when there have come Clouds for some considerable time (suppose an hour or two) the Quicksilver has fallen; and then, upon the Suns breaking out again, it has risen as before. In _Rainy_ weather, it useth to fall (of which the reason is obvious, because the Air is lightned, by so much as falls:) In _Snowy_ weather, likewise, but not so much as in _Rain_. And sometimes I have observed it, upon a _Hoar-frost_, falling in the night. [Sidenote: * _The Author of these Observations intends hereafter more particularly to observe, _from what points_ those Winds blow, that make the Quicksilver thus subside._] For _Windy_ weather, I find it _generally_ to fall; and that more universally, and more discernably, than upon Rain: (which I attribute to the Winds moving the Air _collaterally_, and thereby not suffering it to press so much _directly_ downwards: the like of {171} which we see in swimming, &c.) And I have never found it lower than in high Winds.*