38 REPORT—1857. 
also the mean daily curve of temperature in the sun for forty-two days at Midsum- 
mer. The latitude at Point Barrow is 71° 21’ North, longitude 156° 17’ West. 
On the Grand Currents of Atmospheric Circulation. 
By James Tuomson, C.E., Se. 
In this paper Mr. Thomson brought under the notice of the Section a theory of 
the grand currents of atmospheric circulation, which had occurred to him. It has 
been ascertained as a matter of observation, that in latitudes extending from about 
30° to the poles, the winds, while prevailing from west to east, prevail also in direc- 
tions from the equator towards the poles. Now this motion towards the poles ap- 
pears not to have been hitherto satisfactorily explained. In fact, it is the contrary 
motion to what is naturally to be expected when the theory of Halley, which was 
given about the year 1686, and which appears to afford the true key to the explana- 
tion of the trade-winds, is followed up with respect to the circulation of the air in 
other latitudes than those in which the trade-winds occur. According to this theory 
so applied, it would naturally be expected that the air, having risen to the upper 
regions of the atmosphere in a hot zone at the equator, should float towards the north 
and south polar regions in two grand upper currents, retaining, as they pass to higher 
latitudes, some remains, not abstracted by friction and admixture with the currents 
below, of the rapid equatorial motion of about 1000 miles per hour from west to east, 
which they had in moving with the earth’s surface at the equator. Also, it would 
be expected that the air in the polar regions should have a prevailing tendency to sink 
towards the surface of the earth, in consequence of its increased density caused by 
cold; and that it should tend to flow from the polar regions along the surface of the 
earth, towards the equator, with a prevailing motion from west to east in advance of 
the earth, until, by friction and impulses on the earth’s surface, the motion in ad- 
vance of the earth, brought from above by the air in its descent, and communicated 
further to it by friction and admixture from above, as it passes to lower latitudes than 
its places of descent, is exhausted; or, in other words, until it reaches the latitude 
in which the trade-winds commence to blow from the east; and until it has commu- 
nicated, in blowing from west to east on the earth’s surface, a torsional force to the 
earth, just sufficient to balance the opposite torsional force communicated to the earth 
by the trade-winds blowing from east to west. Now this theory, obvious as it ap- 
pears in the form just adduced, is found in one essential point to be controverted by 
observations. This point is what was stated in the outset of the present article, 
namely, that the prevailing winds on the surface of the earth in latitudes higher than 
30°, are, while blowing from the west, as should be expected, found to blow more 
towards the poles than from the poles; and thus do not move as if impelled along 
the surface of the earth from polar to equatorial regions by an augmented pressure 
due to condensation by cold in polar regions, and a diminished pressure due to rare- 
faction in the equatorial regions. Observations being thus at variance with the only 
obvious theory proposed, the circumstance in question has been commonly regarded 
as rather paradoxical : and Lieut. Maury, one of the most recent writers on the sub- 
ject, has, in his much-valued treatise on the Physical Geography of the Sea, found 
himself forced into supposing an entire reversal in latitudes above 30°, of the great 
circulation just described. 
Mr. Thomson regards Lieut. Maury’s supposition as being entirely unsupported 
by the known physical causes of the atmospheric motions. He, on the contrary, 
maintains that the great circulation already described does actually occur, but occurs 
subject to this modification, that a thin stratum of air on the surface of the earth in 
the latitudes higher than 30°—a stratum in which the inhabitants of those latitudes 
have their existence, and of which the movements constitute the observed winds of 
those latitudes—being, by friction and impulses on the surface of the earth, retarded 
with reference to the rapid whirl or vortex motion from west to east of the great mass 
of air above it, tends to flow towards the pole, and actually does so flow to supply 
the partial void in the central parts of that vortex, due to the centrifugal force of its 
revolution. Thus it appears that, in temperate latitudes, there are three currents at 
different heights :—that the uppermost moves towards the pole, and is part of a grand 
primary circulation between equatorial and polar regions;—that the lowermost moves” 
