344 COJECTURES concernine 
I believe thofe of the Weft-India iflands to be owing to 
fome occafional obftruGion in the ufual and natural pro- 
cedure ot the equatorial trade. This I conjecture from 
the more than ufual preceding calms. In the natural courfe 
of this trade the air rifes up in the line and paffes off to- 
wards the poles, and, in the more contracted degrees of the 
greater latitudes, proves the courfe of their weftern trades : 
So that could this afcent be prevented through the whole 
circle of that zone, there would be no more wefterly winds 
in thefe latitudes than any others. 
Over violent rains and cold naturally tend to check the 
afcent of air out of this circle, rather making it defcend. 
And as there are annual rains in the equator over againft 
thofe iflands, and in fome years more than others, it is eafy 
to conceive fuch an effect, and the confequences. Great 
clouds and over-much vapour generate cold and weight, 
while at the fame time the rains are beating down the air ; 
and as thefe prevent the rifing of the air out of the line, 
fo they hinder its ufual progrefs to it from the tropics on 
both fides. ‘Thus calms muft take place; by which the 
natives ufed to predict approaching hurricanes, without 
underftanding the reafon of the thing. 
Much of calms in the inter-tropical climates caufe ra~-: 
rifactions, and afcents of air into the upper regions, inftead. 
of its being carried to the line to be difpofed of in the 
grand circulation of the atmofphere; this will be the cafe 
more efpecially among the iflands, which increafe the heat 
of the atmofphere. ‘Then by thefe afcents there will be ac~ 
cumulations of air above, which becoming cold in the high- 
er regions will acquire a greater {pecific weight, and be dif— 
pofed to defcend on the firft giving way of the more rari- 
fied and yielding fubjacent region ; and this will be the 
cafe when there happens not to be fufficient motions of 
air in the middle region to keep fmooth and even the ftra- 
tums of the more and the lefs rarified regions; and fo 
prevent particular-portions and places from bending down- 
wards; 
