GRAND CURRENTS OE ATMOSPHERIC CIRCULATION. 
659 
The theory or speculation in the terms in which it was set forth by its author 
makes no reference to the inertial conditions of the atmosphere concerned in its 
diurnal revolution along with the Earth, to which, as a matter of fact, it clings so as 
to have at all times and all places almost the same revolutional speed or angular 
velocity of diurnal rotation as the Earth has. In fact, Halley’s theory would be 
equally applicable to the case of the world being non-rotative and having the Sun, 
or an equivalent source of heat, revolving round it from east to west. 
But, in view of the very powerfully influencing conditions subsequently brought to 
light in the theory of Hadley which will next be adduced, any such feeble causes as 
those relied on by Halley must fall practically into insignificance, the indubitable 
cause shown in Hadley’s theory being such as to be dominant. 
In 1735 George Hadley (brother of the John Hadley who invented the instru¬ 
ment commonly known as Hadley’s Quadrant) submitted to the Boyal Society the 
paper of which I have made mention already as supplying for the first time a substantially 
true theory of the primarily dominant conditions of atmospheric circulation." The 
paper is entitled “ Concerning the Cause of the General Trade-Winds,” and it is right 
here to notice that Hadley applied the name General Trade-Winds, not merely to 
those winds of equatorial regions to which the name Trade Winds is ordinarily 
restricted, but uses it as including also the west to east winds known to be prevalent 
in higher latitudes, and used in trade by mariners for ocean passages from west to 
east. Thus the scope of his theory must be understood as being much wider than 
what would be conveyed in ordinary nomenclature by the name, Theory of the Trade- 
Winds. 
In his paper, Hadley commences by adopting, as a part of the whole truth, the 
view already in his time currently held by others, that the Sun’s heat, intensely 
applied and greatly accumulated in the equatorial regions of the Earth, conjointly 
with the cooler temperatures of the regions in higher latitudes, is the main and 
primary cause of the Trade Winds and other currents of the atmosphere. In this 
way he supposes that at the Equator or near to it there is a belt of air ascending 
because of its high temperature and consequent rarefaction, and an influx from both 
sides towards a zonal region of diminished pressure at its base ; and that from its 
upper part currents float away to both sides, northward and southward, and that 
these continue in the upper regions of the atmosphere advancing pole-ward until, by 
cooling in the higher latitudes, their substance gradually becoming less buoyant sinks 
down gradually and returns towards the equatorial regions as a lower current along 
the Earth’s surface, thence to renew the circulation by ascent again in the equatorial 
region. While indicating virtually that such atmospheric circulation would be 
generated, whether in an irrotative world with a source of heat revolving round it, 
qaestion being, would or would, not the water be set into revolutional motion, and if so would it revolve 
in the same direction as the lamp or other source of heat does P 
‘ Phil. Trans.,’ vol. 39, No. 437, for April, May, and June, 1735, p. 58. 
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