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fatisfy themfelvcs herein by fome Experiments made 
by the late Mr. Hauksbee before this Society, 
though with a different View ; where, by the firing 
of Twenty- fix Quantities of Powder fucceflively, the 
x mercurial Gage was funk from Twenty-nine Inches 
and an half, to Twelve Three-fourths; for by com- 
paring thefe Experiments together, and making the 
neceffary Allowances, it will be found, that the Elafti- 
city was nearly proportional to the Denfity in all that 
Variety of Denfities. 
In this Propofition, the Analogy between the Fluid 
produced by the Explofion of Powder and common 
Air, is eftablifhed thus far, that they exert equal Ela- 
flici ties in like Circumftances ; for this Variation of 
the Elafticity, in proportion to the Denfity, is a well- 
known Property of common Air. But other Au- 
thors, who, fmee the Time of Mr. Boyle , have exa- 
mined the factitious elaftic Fluids produced by Burn- 
ing, Diftillation, &c. have carried this Analogy much 
farther, and have fuppofed thefe Fluids to be real 
Air, endued with all the Properties of that we 
breathe ; particularly the Reverend Dr. Hales , who 
has purfued this Examination with the greateft Ex- 
aCtnefs, in a Series of the belt contrived Proceffes, 
conftantly affixes the Denomination of Air to thefe 
factitious Fluids, he having found, that their Weight 
is the fame with that of common Air, and that they 
dilate with Heat, and contract with Cold,- and that 
they vary their Denfities under different Degrees of 
Impreifion in the fame Proportion with common 
Air; and from hence, and other Circumftances of 
Agreement between them, he fuppofes them to be of 
L 1 1 the 
