and Thoughts_, you may find, that I did some
years agoe think upon this New kind of Baroscope; yet the Changes of the
Atmosphere's Weight not happening to be then such, as I wish'd, and being
unwilling to deprive my self of all other use of the exactest Ballance *,
that I (or perhaps any man) ever had, I confess to you, that successive
avocations put this attempt for two or three years out of my thoughts; till
afterwards returning to a place, where I chanc'd to find two or three pairs
of Scales, I had left there, the sight of them brought it into my mind; and
though I were then unable to procure exacter, yet my desire to make the
Experiment some amends for so long a neglect, put me upon considering, that
if I provided a _Glass-buble_, more than ordinary large and light, even
such Ballances, as those, might in some measure perform, what I had tried
with the strangely nice ones above-mention'd.

I caused then to be blown at the Flame of a Lamp some _Glass-bubles_ as
large, thin and light, as I could then procure, and choosing among them,
one, that seem'd the least unfit for my turn, I counterpoised it in a pair
of Scales, that would loose their _AEquilibrium_ with about the 30th part of
a Grain, and were suspended at a Frame. I placed both the Ballance and the
Frame by a good Baroscope, from whence I might learn the present weight of
the Atmosphere. Then leaving these Instruments together; though the Scales,
being no nicer than I have express'd, were not able to shew me all the
Variations of the Air's weight that appear'd in the _Mercurial_ Baroscope,
yet they did what I expected, by shewing me variations no greater, than
alter'd the height of Quicksilver half a quarter of an Inch, and perhaps
much smaller than those: Nor did I doubt, that, if I had had either tender
Scales, or the means of supplying the experiment with convenient
accommodations, I should have {233} discerned far smaller Alterations of
the Weight of the Air, since I had the pleasure to see the Buble sometimes
in an _aequilibrium_ 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 or the
Ballance, make the Cock vibrate altogether on its side. And this would
continue someti