578 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



be best understood if we take a round table and make it turn hori 

 zontally upon its centre ; it will then appear that the nearer any 

 object is to the edge of the table the faster it moves ; that is, the 

 farther it moves in a given time, and the nearer it is to the centre 

 of the table the slower it moves. In this case the centre of the 

 table represents the pole or axis of the earth, and the edge repre- 

 sents the equator. If we draw a straight line from the edge of 

 the table to its centre, and place a billiard ball on the line, near 

 the edge, and when the table is still, give the ball an impulse 

 directed toward the centre, it will move along on the line to the 

 centre. Now set the ball again near the edge, as before, and cause 

 the table to turn rapidly upon its centre ; let the ball again receive 

 an impulse directed toward the centre, and it will not now move 

 upon the same line that it did before, but will be deflected, gradu- 

 ally, more and more from it to one side, which we will call the 

 eastern side. The reason of this deflection is that the ball carried 

 with it, toAvard the centre, the greater rate of rotary or easterly 

 force which it had acquired near the edge, The water which 

 moves from the equatorial toward the polar regions of the earth is in 

 the same predicament. Therefore, when the difference of tempe- 

 rature — the warmth — impels the water in a current toward the 

 pole, the different rate of easterly velocity — the inertise — impels it 

 eastward. The resultant of the two impulses is (in the northern 

 hemisphere), a movement northeastward and (in the southern 

 hemisphere) southeastward. 



When water moves from the north polar to the equatorial region, 

 the difference of easterly velocity causes it to move southwest. In 

 reality it moves due south, but the rotation of the earth makes it 

 seem to move southwest, because it moves relatively southwest. 

 This will be understood if we place the ball at the centre of the 

 table already described, and when the table is still, impel the ball 

 toward the edge ; it will move in a straight line in the direction 

 of the impulse. Now place the ball in the centre again, and while 

 the tal)le is in rapid rotation, impel the ball as before, toward the 

 edge, and we shall And that it does not pass along the line on 

 which it previously moved, but runs, or is deflected to one side of 

 it, we will call it the west side. The table, in fact, slips past, 

 under the ball, in what we will call an easterly direction, leaving 

 the ball on the west side of the line. Precisely so it is with the 

 current that moves toward the equator. The earth is continually 

 slipping under it, and leaving it relatively more and more west- 



