or falfity, and as to the degrees of worth or ftrength of many rich and STATICS poor metalline mixtures, and other bodies, both folid and fluid; whose fair appearances might, otherwife, have greatly deceived me.

And, to fhew fome curious perfons how far hydroftatics might be ferviceable to as accurate menfurations as need be expected in physical experiments; I defired a virtuofo to mix tin and lead in a certain proportion, unknown to me; and melt them into one mafs; which I carefully weigh'd in water, and also examined it algebraically; and from hence affign'd the refpective quantities of each; which agreed, within little more than a grain, with thofe he had committed to paper, before he mixed them. And this fmall difference, probably, proceeded from fome fcarce avoidable inaccuracies in melting and managing the given bodies.

To conclude; 'tis not to be expected, that the fpecific gravities of the bodies mention'd in the following table, fhall, all of them, be found, in future tryals, precifely the fame as we there exhibit them. For, befides that experiments are made by perfons of different qualifications, with different degrees of care, and with different inftruments; the varieties may proceed from a difference in the texture and compactnefs that may be found in feveral bodies of the fame kind. For, neither nature, nor art, give to all the productions of the fame name, a mathematical precifenefs, either in gravity, or other qualities.

*Dr. Jurin recommends it, as a neceffary caution, to all those who fhall attempt to weigh dry, porous folids in water, for philofophical purposes, that, by fome proper means, they firft extricate the air out of all the fmall pores and cavities of them; whereby the water may have free liberty to enter thereat: otherwife, the air contain'd therein, by keeping the water out, will render the folid lighter in water than it really is. The beft way of avoiding this inconvenience, the Doctor tells us, is to fet the veffel of water, wherein the folid is immerfed, under the receiver of an air-pump, and ex

tract the air out of the body; which will
fucceed the better if the water be firft
heated over the fire: or, in defect of an
air-pump, he directs us to let the folid, if
its texture will fafely permit, continue for
fome time in boiling water, over the firc.
To a neglect of this obfervation, the Doc-
tor thinks, among other things, is owing
that difference found in the accounts of
the specific gravity of the Calculi bumani.
And when the air is thus extracted out of
wood, as oak, fir, &c. and the roots, ftalks,
leaves, and feeds of vegetables, they prove
fpecifically heavier than water. Phil.
Tranf. No. 369, p. 223.

1

The

STATICS.

ATABLE of the Specific Gravities of Bodies compared with Water. *

* Later trials have furnifh'd us with ties of folids and fluids.

the following table of the specific gravi

A TABLE of the Specific Gravities of feveral folid

Ine gold,
Standard-gold

and fluid Bodies.

Quick-filver

Lead

Fine Silver

Standard-filver

Bismuth
Copper

VOL.

-1,190

-1,150

1,130

-1,120

1,040

-1,040

•1,030

1,030

1,030

-1,030

-1,000

AN

Hydrostatical Discourse,

By way of

Answer to the Objections of Dr. MORE, and others, against fome Explanations of particular Experiments:

With farther Confiderations thereon.

F

SECT. I.

Inding no caufe to alter my judgment, as to the folutions I have
given, of fome of my experiments, attack'd by Dr. More; I here
defign to vindicate them from his objections.

nomena, what?

And, firft, the Doctor having made a defcription of my pneumatic engine, Mechanical fo pretends, that the afcent of the fucker, after it is deprefs'd, and clogg'd lations of be with a weight, is not mechanically accounted for, by the gravity and preffure of the atmosphere; becaufe, fays he, "if this folution were truly mechanical, he muft have affign'd the true mechanical caufe of the gravity "of all the parts, and of the whole atmosphere."

To this I anfwer, that in delivering my experiments about the effects of the air, I did not intend to write a whole fyftem, or fo much as the elements of natural philofophy; but having fufficiently prov'd, that the air we live in, is not deftitute of weight, and has an elaftic power; I endeavour'd, by thofe two principles, to explain the phenomena exhibited in our engine; without recourfe to a Fuga vacui, an Anima mundi, or any fuch unphilofophical principle. And fince fuch kinds of explanations have, of late, generally been cail'd, mechanical, as being grounded upon the laws of mechanics, I thought, as I permit, fo I might be allow'd, the ufe of that term; and to entitle my explanations, mechanical, in the ufual fenfe of that expreffion. I am not obliged to treat of the cause of gravity in general, fince many propofitions of Archimedes, Stevinus, and others, who have

Y y 2

written