( 54 * ) 
dral of that University, upon feveral high Mountains 
in Scotland , , and likewife in fome Wells and Coal-pits, 
a particular Account whereof he inferted in his Ars 
magna gravitatis & lev it at is *. I will only obferve, 
that theie Experiments of Sinclair , as well as that of 
Monfieur Eerier , were intended not fo much to lay 
the Foundation of a Calculation, whereby to determine 
the differing Heights of Places, as to prove the Gra- 
vity and Prellure of the Air, a Problem very much 
controverted at that Time, and to fhew, that the fame 
is much more confiderable in Valleys than at the Top 
of Mountains, and hill greater in Proportion at the Bot- 
tom of Wells, Mines, &c. 
But this Matter was purfued hill farther by the 
Members of the Royal Academy of Sciences at Tar is, 
particularly, when by Order of Lewis XIV, they 
drew that expenfive Meridian Line acrofs the ’whole 
Kingdom of France. M. Mariotte , a celebrated Mem- 
ber of that Academy, was one of the firft that laid 
down certain Rules for the Conftru&ion of fuch Tables, 
as might ferve to determine both the Elevation of Places 
above the Level of the Sea from given Altitudes of 
Mercury, and the Heights of the Air, anfwering to every 
Line of Mercury in the Barometer, from 28", where 
the Mercury was fuppofed to Hand at a Medium near 
the Sea. The Principles he went upon, and the Me- 
thod he followed, he difcourfed of at large, in his 
Second Ejfay de la Nature de /’ Air. 
Sometime after, in 1686, the ingenious Dr. Edmund 
Halley went about another Calculation, which he de- 
rived partly from Principles agreeing with thofe of 
* Rotcrodam;, 1669,4/0. pag. 129, J32, i 44 ^ & f e( j 
M . Ma- 
