BuRRELL. — Earth-roiation and Ocean Currents. 265 



clinging tendency, between external bodies and the water is proved by 

 the sun and moon lifting and drawing the tides westward ; and, as the 

 tides are always lagging behind these bodies, they must have a strong 

 tendency to draw the water in a circle towards the Equator on all west 

 coasts, westward near the Equator, and from the Equator on all east 

 coasts, thus causing a stream to flow continually in that direction ; but 

 in reality the sun and moon (and, I suppose, the planets to a small extent) 

 tend to hold the water, and the earth in turning eastward makes the water 

 appear to lag behind ; or, in other words, the water is refarded bv these 

 bodies while the earth rotates eastward. 



This does not necessarily imply that the water would flow at the same 

 rate as the tide, but that the water will have a tendency to be drawn in 

 that direction as if it were slightly downhill. 



This retarding action is continually in operation, and in the same 

 direction. We have the lunar and anti-lunar, solar and anti-solar tides, 

 all tending to induce the water by earth-rotation to move in a circle 

 between the land-masses and the Equator, for the Equator is a boundary 

 when viewed from the centre of rotation, and naturally the water will 

 tend to return eastward in higher latitudes to replace that which is being 

 drawn northward. These latitudes offer less resistance owing to their 

 being nearer to the neutral line between the opposing tides, and also to 

 the fact that the gravitational pull of the sun and moon, acting as it does 

 obliquely to the surface of the water in these latitudes, has a much weaker 

 effect, area for area, than it has on or near the Equator, where the 

 pull, being mostly perpendicular to the surface, must consequently have 

 a greater retarding action on the water while the earth moves on, thus 

 giving the current a westerly trend relative to the land ; or, to put it 

 more briefly, the difference in the gravitational pull on these two positions 

 causes the water to circle clockwise in the Northern Hemisphere and anti- 

 clockwise in the Southern. 



These conclusions w^ere arrived at many years ago, but how to embody 

 the conditions in a working model perplexed me for a long time, for I could 

 not divest myself of the idea that it must be done on a globe ; but at last 

 I began to see a way out of the difficulty. 



If one takes an imaginary bird's-eye view of a hemisphere — say, for 

 instance, the Southern — from a great height above the South Pole, that 

 hemisphere will appear as a rotating disc : in fact, water will behave in the 

 same way on a rotating disc or tray, providing gravity is acting perpen- 

 dicularly to its surface, and this is easily accomplished by having the tray 

 to rotate on a vertical axis, and if necessary we can give it a uniform 

 speed by using a controller. 



So far, then, things are quite simple. All we have to do to represent 

 the Southern Hemisphere is to provide a shallow circular tray mounted 

 on a vertical shaft, with the different land -masses^ South Africa, South 

 America, Australia, Antarctica, and a few of the larger islands — modelled 

 in wood, placed in the tray and fastened in their relative positions and 

 almost submerged in water, and then to rotate the tray at a uniform speed. 

 But by doing this we are confronted by another difficulty, for if we give 

 the tray a uniform speed how are we to give the water the very necessary 

 retardation without in any way interfering with its free movement ? 



To overcome this difficulty, instead of giving the tray a uniform move- 

 ment for a long period, I gave it an accelerating movement for a short 

 period by means of a falling weight just sufficient to put it in motion. 

 I wish the point to be thoroughly" understood, that accelerating the land 



