Hydrostatics.

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’tis evident the Hydrometer cannot fink sofar into the heavy or strong Fluids, as intothose which are lighter or weaker. Theseveral Degrees of Strength, therefore, areeasily shewn by the graduated Neck of thisInstrument (LXII).

The

(LXII) 1. The Hydrometer is one of the most use-ful Instruments of the Philosophical Kind ; for tho’ theHydrostatic Balance be the most general Instrument forfinding the specific Gravities of all Sorts of Bodies, yetthe Hydrometer is best suited to find those of Fluids inparticular, and with the greatest Fase, Conveniencyand Expedition, as will appear from the following Ac-count, and Description thereof.

2. This Instrument consists of four principal Parts,viz. (1.) A large round hollow Ball or SphereA B C D, which is made of Ivory, Glass, or Metal, asCopper, Brass, i$c. (2.) An hollow Glass-Ball E C,'of a smaller Size, partly fill’d with Quick-silver screw'don to the lower Part of the former, in order to renderit but little specifically lighter than Water, that it maynearly sink in it. (3.) A long small Stem or ShankA F fix’d into it on the upper Part, which by itsWeight causes the Body of the Instrument to descend inthe Fluid with Part of the said Stem. (4.) A smallWeight F, screw’d on upon the Top of the Stem orWire AF, to cause the Instrument to sink so far, thatthe Surface of the Fluid may always cut the Stem in itsmiddle Point G.

3. Tho’ the above be the usual Structure and Com-position of this Instrument, it is certainly not the best ;for if the Body or Globe ABCD be of Ivory, it willimbibe Part of the Liquor, and so its specific Gravitywill be alter’d, and consequently the Experiment can-not be just. If it be of Glass, it will be subject tobreak, and will stand in need of Screws, Solder, Lea-ther, &c. to make the Parts tight, which will befound also both inaccurate and inconvenient. The bestWay therefore is, to have it made of Metal, viz. ofCopper; with a Brass Stem above, solder’d on ; and

a Brass