in order to af certain the height of Mountains. 557 
much more Ample method of arriving at this theory, 
than either he or I have fince purfued. It was this; to 
determine hydroftatically the fpecific gravities of air^ 
and quickiilver, with a given temperature and preffare ; 
the increafe of volume, or change of gravity, with a 
given increafe of heat being fuppofed to be known by 
the experiments of boerhaave and hawkesbee (, \ 
which might be farther examined by fimilar ones ; and 
prefuming that the geometrical ratio in the air’s den fity, as 
you advance upwards from the earth’s furface, had been 
fufficiently demonftrated^. For the proportional gra- 
vity of quickiilver to air will exprefs inverfely the length 
of two equiponderant columns of thefe fluids, that is, 
when the columns are taken infinitely fmall {x) . With 
thefe 
(r) It may feem particular that I ftiould propofe an experiment fuppofed to 
be very well known, and which hardly any elementary treatife on chemiftry or 
experimental philofophy will not furnilh us with an example of; the weight of 
a given quantity of air. boyle, halley, hawkesbee, hales, each of 
them have tried it, and many others fince their time : but the misfortune is, all 
thefe experiments have been but grofs approximations, without due attention to 
the heat ; and yet the determination of hawkesbee feems to have b:en followed 
by one half of Europe in Pneumatical refearches. Indeed I only know of one 
experiment that has the leaft title to precifion, and that is Mr. caven- 
dish’s, briefly related in the LVith volume of the Philofbphical Tranfa&ions. * 
(5) Elementa Chemise. 
(t) Phyfico-mechanical Experiments. 
(u) cotes’s Hydroftat. Leflures, et alibi . 
(x) I am not forry to anticipate the reader’s remark here, that this obfer- 
vation is not new; fince I find that I have been treading the fame fieps with 
Mr, 
