7 5 2 Co/. roy’s Experiments for 
that quarter have been the greatefh Thus the 
North-eaft wind, by blowing for any length of time, 
brings into the middle latitudes a mafs of air heavier 
than that which naturally appertains to the region, and 
raifes the barometer above its mean height. The con- 
tinuance of a South -wefter carries off the heavy air, de- 
ports a much lighter body in its Head, and never fails 
to fink the barometer below its mean height: hence, 
in the middle parts of Europe, there is a difference of 
about two inches and a quarter between the higheft and 
lowed: flates of the barometer. But fuppofing it to be only 
two inches, the difference of preffure ff ill amounts to 
77th part of the whole weight of the atmofpliere. Now 
it is evident from the Peruvian obfervations, that the 
greateft fluctuation of the barometer, which is at the 
level of the fea, doth not exceed 0.226 of an inch, or 
~d part of the whole prelfure ; and if the change fhould 
be no greater at the poles, which I think not impro- 
bable, it follows, that the meafurement of heights by 
means of the barometer, in middle latitudes, will be 
more precarious and uncertain than in the torrid and 
frigid zones. 
Such in general were the firft ideas which the compa- 
nion of the operations of the barometer with the effeCls 
