Hydrostatics.

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P, shew at once the specific Gravity of the SolidR to that of the Fluid TV (LXIII).

The specific Gravity of Fluids is rea-dily determined by weighing one and the

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(LXIII) 1. The Reason why I have given no Ac-count or Figure of the Common Hydrostatic Balance, isbecause it is every where to be found in Books of thisSort; but principally, because I would advise Gentle-men to the Use of that exhibited in the Lectures, whichthey will find far more expeditious and exact, and there-fore much better fitted to answer the End of such anInstrument. For this Method of suspending the Solidto be weighed by a Horse-Hair, or fine Silk, requiresnot the large heavy Glass-Bucket (as in the Common Hy-drojiatic Balance) to find the specific Gravities of Solids;or the heavy Glass-Bubble to find those of Fluids; andtherefore the Weight being reduced, the Balance maybe smaller and nicer, and consequently such as willturn with a lesser Difference of Weight.

2 . The different Gravities of Solids being first com-pared with that of Water, are then easily comparedwith each other; for let S be the Weight of one Solid,§ the Weight of any other, and W the Weight ofWater, all of equal Bulks ; and let S : W :: 5 : 1,and s : W :: 7 : 1; therefore 5 W = S, and 7 W — s ;consequently S ; s :: 5 W ; 7 W :: 5 : 7 ; that is, thespecific Gravities of the Solids S and s are as 5 to 7.And in the same Manner the specific Gravities ofFluids are compared, being first compared with that ofany one Solid.

3. As the very Notion of specific Gravity impliesComparison, so there must be some Sort of Body fixedupon, whose Gravity must be made a Standard for theGravities of other Bodies of equal Bulk to be comparedwith. This Standard Body must have two Properties ;first, it must be easy to be had or come at upon allOccasions ; and secondly, it must be of a fixed unal-terable Nature, or at all Times the same, that theremay be no Variation of its Gravity in equal Bulks, indifferent Times or Places. Now it is certain such aBody must be of the Fluid Kind, because the best Wayof finding specific Gravities is by Immersion.