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THE weights made use of are the common ones of the gold-smith; the pound consisting of twelve ounces; the ounce of twenty-penny weight; and the penny weight of twenty-four grains. We make choice of pure gold for the standard, and adjust the dimensions of the other bodies thereto; because this is not only the heaviest substance we know; but also the most uniform, homogeneous, and without any volatile part. The experiments, upon which the table was formed, proceeded thus.

We fashioned an ounce of pure gold into a solid cube, and provided a square case, or box of silver, which contained and fitted it exactly; excepting only, that the case rose somewhat higher: but a line was drawn on the inside of it, at the precise height whereto the gold cube reached. This we did for the convenience of filling the case with fluids, and powders; so that when either of them were put in, they might not run over, or be spilt; but contain themselves level within. We likewise provided another similar case, perfectly of the same weight and dimensions; in order to shew the proportion which the body, contained in one, bore to that contained in the other. Then cutting cubes

of the same dimensions, or bulk, with that of the gold, in all the solid bodies specified in the table which would bear cutting, we fitted them exactly into the cases, up to the line; and poured in our liquors to the same height occasionally. The like we also did by the powders; constantly observing to squeeze and press them in so strong, that they might lie even and uniform, without subjecting our experiments to casualty.

Then for the trials themselves; we put one of the cases, empty, in one scale, and the other case, containing the body to be examined, into the other scale of the balance; and separately took the exact weight of each body so contained. For, as much as the weight of the body fell short of that of the gold; so much the bulk of the body exceeded that of the gold. Thus, for example, as the gold cube weighed an ounce, and an equal cube of myrrh, weighed but one penny-weight; it follows, that the bulk of myrrh is to the bulk of gold, as twenty to one: so that there is twenty times as much matter contained in gold as in an equal bulk, or dimension, of myrrh; or, again, twenty times as much bulk, or distention in myrrh, as in an equal weight of gold.


1. The vessel here employed, would not, on account of its smallness and figure, allow the

experiments to be made with any great exactness by its means we could not easily take the specific gravities below a quarter of a grain; and the little square surface of the matter, might by a small and insensible rising, make some difference so that vessels rising sharp and conical, are best suited for forming an accurate table of this kind*.

2. No doubt but many of the bodies expressed in the foregoing table, have a greater or less specific gravity than others of the same kind; so that one wine would contain more matter in the same space, than another; and one wood more than another wood of the same species, &c. And therefore the business of exact trials, and settling the accurate proportions of the specific gravities of bodies, is here somewhat uncer tain, or casual. Nor can it be expected that the individual bodies we made our experiments with, should be a standard of the nature and gravity of each species; or that they should perfectly agree with the experiments made by others, in the same mannert.


*As in M. Homberg's glass for taking the specific gravities of liquors; where a single drop is made to possess a considerably long space in the slender graduated neck.

*To this may be added the different seasons of the year, and times of the day; as to heat and cold, dryness, and

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3. We have received into our table, only such bodies as would commodiously occupy and fill up space; whilst the body remained as it were entire, uniform, and similar: and such also as have a sensible gravity in the air; from which gravity we might judge of their quantity of matter. So that there are three kinds of bodies whereto our experiments were not applied; viz. 1. those that are uncapable of a cubical dimension; as leaves, flowers, pellicules, membranes, &c. 2. such as are unequally porous and cavernous; as sponge, cork, wool, &c. And 3. untangible bodies, whose weight is not perceived in the air; as flame, air itself, &c.*

4. Enquiry should be made, whether, possibly, the close contraction or condensation, of a body, by an uniform force on all sides, will give it a greater proportion of gravity, than corresponds to its quantity of matter. This enquiry belongs to the particular history of gravity†: and if it terminate in the affirmative, our calculation must needs be erroneous; and the more rarified

moisture, &c. All which occasion variations in very curious experiments of this kind.

*These experiments require the assistance of the airpump.

+ This history the author intended to write; but it was not published.


any body is, it will contain somewhat more matter under the same bulk, than is assigned it by our method*.

This table I made many years since; though, as far as I remember, with tolerable care and exactness: but, doubtless, an infinitely more accurate one may be formed, from trying a greater number of bodies, and in larger quantities; which greatly contributes to render the experiments more just. And this being a fundamental thing in philosophy, it should by all means be procured+.

*This point may now seem settled, by the industry of the moderns; since it is shewn, by experiment, that quantity of matter and absolute gravity are reciprocal; or that the matter in bodies corresponds exactly to their weight. The question here turns upon the distinction betwixt absolute and relative, or specific gravity. Absolute gravity is the weight of bodies in a perfect vacuum, or unresisting medium and relative gravity, their weight in a resisting medium; which lessens the absolute gravity of a body, in proportion to the density of the medium. So that the same body weighs less in air than in vacuo; less in water than in air, &c. Therefore, in the present case, where the experiments are made in the air; the condensation of a body, by lessening its surface, will cause it to be less resisted by the air; and consequently to weigh the more. But in an absolute vacuum, the same body ever so much condensed. weighs no more than the same body ever so much expanded

+ There are several tables of this kind extant; though none perhaps so copious and extant as is on many occasions

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