ia 6
VVJUJDS.
R E M A R K S o n t h e
Having palled the tropic o f Cancer again, we found the wind,
"became more Ealleriy, viz- E . N . E . and even fometimes E . by
N . Ha lf E . ; till, in 270 or 2 8° N orth latitude, we again met with
the variable winds.
From this circumltantial account, the following inferences may
b e drawn.
. Firji, T h e trade-winds extend fometimes beyond the tropics into
the temperate zones, efpecially when the fun is in the fame hemisphere
; and the extent o f the trade-winds within the tropics, feems
to be proportionate to the fun’s diftance in the oppoiite hemilphere.
■ Secondly, T h e trade-winds in the South-Sea, are fometimes interrupted
by calms and contrary Wefterly winds; and in particular,
' rains and thunder-florins are not uncommon at thefe changes.
‘Thirdly, Th e trade-winds arei likewife fometimes interrupted at
the approach of land, efpecially i f it be o f confiderable height.
Fourthly, A t the intervals, where one wind leaves off and the
other fets in, commonly calms, and not feldom rains, are to be
met with.
It has hitherto been allowed, that, in the fpace within the tropics
in large oceans, the regular winds reign, which come from
the E a ilj and the caufe o f this is thought to be the fun, which,
being vertical, or nearly fo, within the tropics at noon, rarefies the
air, as his effedl is then moll powerful: but, as the fun is every
6 moment
a t m o s p h e r e . 127
moment advancing to the meridian o f fome other place on the globe,
the rarefied part o f the atmolphere o f courfe moves from Eall to
Well.. As loon as the caufe o f the rarefaction. ceales by the removal
o f the fun,, the columns o f air in the neighbourhood of the rarefied
place, rulh in to caufe an equilibrium. T h is ’ current forms the.:
trade-wind,, and gives-it continuance,, within and near the tropics-
Th e caufe,. however,, is not fo general, as that it may not be altered
by fome more powerful agent; fuch as the vicinity o f land, or a-
«loud pregnant with vapours and eledtric matter.
Though the lands in the South-Seas be o f no confiderable extent,
they have however,, generally, the benefit o f the fea and. land—,
breezes; lb that the reigning trade-wind only operates in the day
time on the windward-fide o f the file, and, afterwards follows the
diredtiori o f the fhores, and falls every where, perpendicular, or
nearly fo, upon them; nay, on the lee-fide of the ille, it becomes;
contrary to the trade, but extends only a few. miles more or lefs
out to fea, in proportion to the fizeo f the land and other, accidental
caufes. In. the night-time,, the fame, wind,, as-it were, returns and,
goes out to fea from the land,, keeping within, die common, limits,
©f thefe alternate breezes.
As the Ealleriy winds reign with a peculiar conllancy within die:
tropics, it has been likewife obferved, that, without, them, the:
Welterly ones are. the moll general, but their conllancy, both in.
Iheugthi
WINDS.