376 



DISCOVERY 



owing to the difference of sjx-eds a relation arises in 

 which, compared with the solid earth, the oceans 

 appear to move from east to west. 



It is to be noticed, further, that the surface water in 

 the tank tends most to " slop over." This is not only 

 because the surface water is nearest the edge of the 

 tank, but also because it enjoys a greater freedom of 

 movement tiian the under water. In the case of the 

 under water an extra condition is imposed by the fact 

 that it is kept down by the weight of the water above 

 it. Thus it is constrained to a greater degree than the 

 surface water, and thence it is invested with a certain 

 rigidity or immovableness. For, acting in conjunction 

 with the downward pressure from above is the rigidity 

 forced upon it by the presence of the walls of the tank, 

 which prevent its motion outwards and by resistance 

 hold it back. In other words, the lower portion of 

 water is encased by inwardly directed force pressures 

 on all sides around. This docs not occur to the same 

 extent in the case of the surface water, which, even 

 though the tank walls extend to a height above it, can 

 find a freedom of movement by splashing upwards, 

 no weight of water being above it to press it down. 

 Applying 4his conception to the magnified conditions 

 of the oceans, where in some cases the height of the 

 waters above the floor-bed is measured in miles, the 

 gigantic pressures which must necessarily result in the 

 lower deeps, will confer on the liquid water an immense 

 rigidity, and by the enormous weight above, a frictional 

 grasp of the surface of the rigid earth crust beneath 

 the waters, as will cause them to be rotated with the 

 solid earth almost entire. This rigidity, as will be 

 seen, will diminish as the free surface of the water is 

 approached. Corresponding to the sides of the tank 

 are the raised parts of the ocean bed rising to dry land, 

 and it is these which keep the waters in, while the 

 gently sloping shores of the land offer that minimum 

 of resistance as would allow the extreme surface 

 movement of the waters over them, resulting from 

 their slipping back from the main movement of the 

 earth. Hence, in the consideration of ocean currents, 

 we arrive at the natural condition that such currents 

 will be mainly surface currents, and will not materially 

 extend to the great depths of the oceans. The greatest 

 depths of ocean currents are supposed not to be more 

 than about i,6oo feet, or, roughly, one-third of a 

 mile. 



When any homogeneous rigid body is rotated it is 

 necessary, in order to prevent strain, for the outer 

 layers to move at a greater speed than the inner or 

 more central portions. Similarly, in a globe where 

 the axis of rotation is a diameter, it is necessary for 

 the polar layers, which are nearer to the central axis 

 than the equatorial surface layers, to rotate at a 

 slower speed than the latter. This occurs in the rigid 



body, the earth. In one rotation, a point on the 

 Equator is carried 25,000 miles ; a position in Lat. 40. 

 19,250 miles ; at the Poles the distance of rotation 

 becomes infinitely small. Thus, there is a graduating 

 speed from Equator to Poles, the equatorial region 

 being moved the fastest, viz. 25,000 ~ 24, or 1,100 

 miles per hour. 



According to the speed at which the solid earth and 

 the waters above it are travelling, so the lag of inertia 

 in the waters will have effect. At the Equator, 

 therefore, the lag will be most pronounced, and the 

 current there formed will be the main current of the 

 world to which all lesser currents must subserve. If 

 the earth is imagined entirely covered with water of 

 uniform depth, we should then have a main ridge 

 current round the Equator performing a continual 

 circle of movement from east to west. On either side 

 of this will be lesser currents. All these waters of the 

 earth would wash round in a direction opposite to the 

 direction of rotation of the earth, and these currents 

 would be parallel to the Equator, and they would move 

 at different speeds, but the resultant movement \rith 

 the solid earth will be of rotation in the same direction. 

 The lag of the currents, it might be pointed out, will, 

 by the friction caused, tend to create a " brake action " 

 on the earth's rotation, similar to that of the tides 

 hypothesised by Kant ; but complementary action 

 arises to nullify this. 



Looking at the map of the world, we find the ideal 

 case above very much modified, but the intrinsic 

 nature is not blotted out. Both in the Pacific and the 

 Atlantic the north and south equatorial currents fonn 

 the main feature. Instead of an ocean of uniform 

 depth enveloping the earth, land masses arise between, 

 and by their interception break up the continuous 

 oceanic circulation above hypothesised. It is evident 

 that the flow continues until land is approached, and, a 

 collision taking place, the current is laterally deflected 

 on either side, so that one branch flows north and the 

 other south, the while continuing to exert their western 

 tendency, as is seen by the " hugging " of the eastern 

 shores of the continent approached. This throwing 

 of the waters to the west is clearly seen, not only in 

 the equatorial regions but in the regions approacliing 

 the Poles. The Labrador Current, the East Greenland 

 Current, the Oya Siwo of East Siberia, are examples 

 of this, though, as we shall see, the equatorial direction 

 also enters in to cause that same hugging of the eastern 

 shores. Thus, Land Masses become an important 

 factor in the question of Ocean Currents ; and though 

 they do not originate the causes of flow, they enter as 

 modifying agencies in disposing the final form of the- 

 complete currents. 



{To be continued) 



