128 
The Australasian Scientific Magazine. [Nov. i, 1885. 
commencing at the tropics would deviate but a few points of 
the compass from north or south and gradually approaching more and more 
nearly to due north and south winds respectively would finally end as 
such where they cease and ascend on the confines of the equator itself. 
Through their whole course, however, the trade winds are on an average 
N.E. and S.E. winds, axial rotation simply operating to make their angle 
of inclination slightly larger at the tropics than at the equator. Such 
being the limited extent of the influence exercised by axial rotation on 
currents of air between the tropics, the theory advanced in explanation of 
the trade winds does not meet the requirements of the case as already 
affirmed. 
Having seen that there is in reality no theory whatever as yet suggested 
which explains the general circulation of the waters of the ocean, or of the 
atmosphere which surrounds our globe, let us enquire in what manner the 
influence of the sun and moon is exerted on both air and water. The 
attraction of these bodies would have no effect whatever on anything on 
the surface of the earth directly under them, for the force with which any 
object is attracted towards the centre of the earth is always greater than 
the attraction of the sun and moon, even when in conjunction. If this 
were not the case, then everything moveable would be drawn away from 
the earth altogether, never to return. But the attraction of the sun and 
moon must exert great influence on those parts of the earth which are 90 
deg. distant in every direction from the points on the earth’s surface lying 
in the straight lines joining their centres with that of the earth, i.e., the 
points directly under the sun and moon respectively, because the force 
which they exert on those parts and the force of gravitation towards 
the centre of the earth are here acting at right angles to one 
another instead of in opposite directions. Particles of air, there- 
fore, at either pole being operated upon by two forces at right 
angles to each other, will obey neither the one nor the other, but will 
move in a line between, that is, they will rush from the pole towards the 
equator. The influence thus exerted will be greatest in amount at either 
pole — possibly the only force to be overcome here is friction — and it will 
diminish in intensity as the equator is approached. A glance at a terres- 
tial globe will show that practically the minimum of this force would be 
reached at about 30 deg. north or south. Indeed, the whole torrid zone 
may be regarded as being directly under the sun and moon. A lin - join- 
ing either tropic with the centres of the earth and sun or the eartn and 
moon w r ould diverge very little from a straight line, and, therefore, li tie or 
no motion would be the result. Here, then, we have evidently a cause 
— a combination of forces overlooked by scientists in this connection — 
which satisfactorily explains the upper current in the atmosphere, known 
to exist in extra-tropical regions, and the reason for which has hitherto 
proved so “ hard to conceive.” The sun and moon are constantly em- 
ployed in pulling the air away from the polar regions and piling it up at 
the tropics. At these parallels there must therefore be an increased 
barometrical pressure, the result of which is that as the sun and the moon 
can only operate on one side of the earth at a time a surface current is 
forced to move from the “ horse latitudes ” towards the poles. This surface 
current being in extra-tropical regions, where the difference of measure in 
the earth’s circuit on successive parallels is very marked, will of course be 
considerably affected by axial rotation This, and the direction in which 
the pressure of the atmospheric tides is exerted, with perhaps other causes, 
