( 47 ) 
with the fame fenfible Velocity againft the quiefcent 
Atmofphere ; but that this Dilatation would be 
greater, if the Atmofphere had a Flux or Current in a 
Direftion contrary to that of the Wind. 
Mr. Gerjlen demonftrates in the next Proportion , 
that a perpetual Eafterly Wind will reign in all 
Places within the Tropics, arifing from the diurnal 
Heat; and that this Wind will diffufe itfelf to the 
other Regions without the Tropics, and have a Di- 
reQion declining from the Eaft towards the North 
or South, according to the Situation of the Region 
on the terreftrial Globe; that its Morion will be 
more remifs, the nearer the Places are to either 
Pole, and that the Angle of Declination from the 
Eaft will be greater for the fameReafon. 
The preliminary Propolitions being thus fettled, 
he proceeds in Prop. XIX, to account for the riling 
and falling of the Mercury in the Barometer thus. 
The Air of the Atmofphere in our Regions has a na- 
tural Motion or Current, whofe Direftion is fitua- 
ted between the Eaft and NorthPoints of the Com- 
pafs. If therefore a fpecial Wind Ihould fpring up 
and blow in a contrary Direftion, it will produce 
tremulous Vibrations, and confequently Dilatations 
of the Air ; then equal Bulks of the dilated Air 
dilated, will have a lefs Quantity of Matter than 
before: Therefore the Gravity of the Air will be 
lefien’d, and by Confequence the Qiiickfilver in the 
Weather-Glafs will fall. And this Decreafe of Gravity 
in the Air, and of the Height of the Mercury in the 
Barofcope, will be proportional to the Greatnefs of the 
Force of the Wind and Degree of Oppolition of its Di- 
reftion to that of the Flux of the Atmofphere con- 
un&ly. This 
