129 
Nov. i, 1885.] The Australasian Scientific Magazine. 
will make them south-west and north-west winds, instead of being otherwise 
due south and due north winds respectively. 
Within the tropics everything on the earth’s surface is passing and re- 
passing under the influence of the sun and moon at the rate of 1000 miles 
an hour. Here their attraction exerted in the manner explained above 
can only make itself felt in retarding the motion of both airand water, and 
thus giving to each a westward tendency. And as air is much more easily 
moved than water, their effect in retarding the atmosphere in equatorial 
regions must be considerably greater than their effect upon the water ot 
the ocean. This will account for the westward tendency of both wind 
and currents, and the mobile nature of air explains the greater velocity of 
the former. It is in this zone that the sun’s heat operates as an agent on 
the motions of both air and water. Its effect is of course also much 
greater on the atmosphere, and hence, by rarifying the air at the equator 
and thus causing an upward motion, it is found sufficient to make the trade 
winds north-east and south-east winds in their respective hemispheres, in- 
stead of blowing from east to west as they would otherwise do if not 
affected by heat. The upper and return currents from the equator to the 
tropics will also have easting in them being retarded as before mentioned. 
They will therefore blow from the S.E. in the northern, and the N.E. in 
the southern hemisphere. At the tropics these currents will strike against 
the immense wall of air which is here erected and sustained by successive 
atmospheric tides flowing from the poles. Here they must descend and 
move off again towards the equator as the north-east and south-east trades 
once more ; and so on ascending at equatorial and descending at tropical 
calms continually. 
The waters of the ocean are, comparatively speaking, but slightly 
affected by the heat of the sun. The general direction of equatorial 
currents therefore, whilst corresponding with the upper currents of the 
trade winds, will be more from east to west. The intervention of land 
running from north to south causes them to be deflected out of their 
course and gives rise to the Gulf Stream, the Japanese, and other currents. 
The surface currents from the poles are to be accounted for in the same 
way as the upper current in the atmosphere, viz., by the attraction of the 
sun and moon acting at right angles to that of gravitation towards the 
centre of the earth. These polar currents are easily set in motion, as 
nothing but friction has to be overcome. By this means the surface 
waters of the polar regions are drawn towards the tropics to supply the 
place of the warmer waters from equatorial regions which force their way 
to the north. Making the necessary allowances, therefore, for the inter- 
vention of land, and water also being less easily affected by the sun’s 
heat than air, the general direction of the surface currents of the ocean 
should be found to correspond with the direction of the upper currents of 
the atmosphere as already described, and that such is the case a careful 
examination of Maury’s charts will demonstrate. 
That the attraction of the moon is sufficient to put the great equatorial 
currents in motion from east to west, and thus give rise to the Gulf 
Stream flowing to supply the place of the polar currents travelling 
towards the equator, any student of astronomy will admit. To prove this 
by reference to authority would be superfluous. Attention has therefore 
been directed to two existing forces, recognizable by all, the combined 
operation of which explains the whole of the movements taking place in 
our atmosphere, and also the general direction of oceanic currents. The 
