( t \ l ) 
rence of Degrees in that Latitude, which they make of 
3 1 Toifes. And that there was a Miftake of this Kind 
in taking the Height of that Mountain, I (hall (hew. 
The Vapours, that generally float in the Air about 
the Tops of high Hills, make it fo difficult to take their 
Height exaftly, that Experiments, made with the Ba- 
rometer, will, by obferving the Fall of the Mercury , 
ffiew the Height nearer than any Thing elfe we know 
cf. There were, indeed, feveral Experiments made 
with the Barometer,* where the Differences of the Height 
of the Mercury , from the Heights at which it (food at 
the Royal Obfervatory , are faid to anfwer to fo many 
Toifes ; but of nine Obfervations mention’d by Monf. 
CaJJini , there are not two where the Number of Toi- 
fes, faid to correfpond to the Heights of the Barometer, 
do agree together. i 
The fir (l Experiment of the Barometer there men- 
tion’d, made at Qollkure , was this, “ At the Height 
a of iis Toifes above the Sea, the Barometer was fet 
u U p 5 an d the Mercury (food 3 f Lines higher than at 
“ the Royal Obfervatory (in the Tower of the eaftern 
« Hall) at the fame Time ; and therefore, fince that 
Tower is 44 Toifes higher than the Sea, 3? Lines 
tC of Mercury muff anfwer to 31! Toifes. . 
Now, reducing thefe Toifes to Feet, and dividing 
by 3 l it will appear that an Height of 5*8, ? Feet will 
anfwer to the Fall of one Lurie of Mercury in the Ba- 
rometer. Let this be taken as the Standard, and the 
other Obfervations be compar’d with it. This may be 
done by the following Table, where the firft Column 
fhews the Place where the Obfervation was made ; the 
fecond, the Fall or Rife of Mercury at each Place ex- 
nrefskT in Lines, or ixth Parts of a French Inch •, the 
H h 2 third. 
* Mew . of the Royal Academy, for] 7 \ij ch. 10. 
