286

Hydrostatics.

same solid Body in them severally; forsince we suppose the Balance in Equilibria

with

4. Among Fluids there ate none which promise theRequisites for a Standard so fairly as Water. Yet herewe find various Kinds, and of different Gravities, andnone which are quite unexceptionable. Rain Wateris the most so of any, (but this is not always at Hand)its specific Gravity being so nearly always the fame,that could it be always had, it would answer all ourPurposes very well. However, common Water, bymeans of the Hydrometer, might be always made aStandard in the following Manner.

5. Let there be a Quantity of Salt dissolved inSpring-Water to give it a Body or Density, a littlegreater than any Water of that Kind can be supposedto have naturally. Then let a very exact Hydrometerbe set to float therein, and observe at what Division ofthe Neck the Surface of Water stands; and that willbe the Point, to which the Hydrometer ought to sinkin the Water designed for these Experiments, andwhich it may easily be made to do by the Solution ofSalt therein, or a Mixture of Salt-Water therewith.And a better Method than this, for procuring a Stan-dard Fluid, I am not able to think of.

6. By this Method I only propose to fix a Standardfor very nice Enquiries ; but for common Uses, commonWater will do, whose Gravity must be represented byUnity or 1, or (in case of constructing Tables withgreat Accuracy) by 1,000, where three Cyphers areadded to give room to express the Ratios of otherGravities in larger Numbers in the Table. In doingthis, we have a twofold Advantage; the first is, thatby this Means we can express the specific Gravities ofBodies to a much greater Degree of Accuracy and Ex-actness. The second is, that the Numbers of the Tabledo also express the Ounces Averdupois contained in acubic Foot of every Sort of Matter therein specified,because a cubic Foot of common Water is found, byExperiment, to weigh very nicely 1000 Ounces.

7. Now an Ounce Averdupois weighs 437-*- Grains,

and