Page:Philosophical Transactions - Volume 001.djvu/244

 far smaller Alterations of the Weight of the Air, since I had the pleasure to see the Buble sometimes in an æquilibrium with the counterpoise; sometimes, when the Atmosphere was high, preponderate so manifestly, that the Scales being gently stirr'd, the Cock would play altogether on that side, at which the Buble was hung; and at other times (when the Air was heavier) that, which was at the first but the Counterpoise, would preponderate, and, upon the motion of the Ballance, make the Cock vibrate altogether on its side. And this would continue sometimes many daies together, if the Air so long retain'd the same measure of gravity; and then (upon other changes) the Buble would regain an æquilibrium, or a preponderance; so that I had oftentimes the satisfaction, by looking first upon the Statical Baroscope (as for distinctions sake it may be call'd) to foretell, whether in the Mercurial Baroscope the Liquor were high or low. Which Observations though they hold as well in Winter, and several times in Summer (for I was often absent during that season) as the Spring, yet the frequency of their Vicissitudes (which perhaps was but accidental) made them more pleasant in the latter of these seasons.

So that, the matter of Fact having been made out by variety of repeated Observations, and by sometimes comparing severall of those new Baroscopes together, I shall add some of those Notes about this Instrument, which readily occur to my memory, reserving the rest till another opportunity.

And First, if the ground, on which I went in framing this Baroscope, be demanded, the answer in short may be; 1.That, though the Glass-buble, and the Glass-counterpoise, at the time of their first being weigh'd, be in the Air, wherein they both are weigh'd, exactly of the same weight; yet they are nothing near of the same bulk; the Buble, by reason of its capacious cavity (which contains nothing but Air, or something that weighs less than Air) being perhaps a hundred or two hundred times (for I have not convenience to measure them) bigger than the Metal line counterpoise. 2.That according to a Hydrostatical Law (which you know I have lately had occasion to make out) If two Bodies of equal gravity, but unequal bulk come to be weigh'd in another Medium, they will be no longer Rh