( 2'3 ) 
imagine, that the Number of Toifes nam’d, was al- 
ways proportionable to the Fall of the Mercury , and 
think all the Experiments and Obfervations very accu- 
rately made, when they feem to agree fo well in every 
Re r pe<ft. 
Now after all, I do not queftion but that the Height 
o f the Barometer, might be as it is fet down in the Me- 
moirs, and well enough obferv’d j but it was wrong to 
compare the Height of the Mercury in the South of 
France , with the Height that the Mercury was at in 
the Barometer of the Royal Obfervatory at the fame 
Time • for, at that great Diftance and Difference of 
Latitude, the Weather" (and conlequently the Prelfure of 
the Air and Height of the Barometer at the fame Level) 
might very much vary. 
Even when there is fair Weather all over France , it 
does not follow that the Barometer {hall ftand at the 
fame Height. Let us fuppofe, for Example, that a 
North Wind blows: Where- ever the Airis check’d by 
a Chain of Mountains that run Eaft and Weft, it will 
be accumulated over thofe Mountains, and confequently 
prefs more a3 its Columns are higher ; which will make 
the Mercury rife higher than it wou’d do with the 
fame Wind, if there were no Mountains, or if they ran 
North and South. 
The Way,, to have made the Experiments with the 
Barometer exactly, wou’d have been to have obferv’d 
the Height of the Mercury at the Bottom and at the 
Top of the Mountain, and that with a Tube of a pretty 
large Bore (with a proportionably large Ciftern for the 
ftagnant Mercury') becaufe, in a fmall Tube,, the Mer- 
cury will often flick to the Sides,, and rife irregularly, as 
it will alfo in inclin’d Barometers. Simple Barometers 
are the beft, and a magnifying Glafs may be made ufe 
i of 
