136 THE OCEAN RIVER 



one side to the other — in any direction. After the disc has 

 stopped it will be seen that the pencil mark is actually a left- 

 handed curve. But the northern hemisphere of the earth moves 

 in the opposite way from the phonograph disc; therefore what 

 would be a straight line to an observer fixed in space is to us 

 a right-handed curve. 



The Coriolis effect was noted in a general way by Humboldt 

 in 1814 when he wrote: ''Considering the velocity of the fluid 

 elements which, in different latitudes, in consequence of the 

 earth's rotation, is different, one should be tempted to think 

 that every current from south to north ought to have at the 

 same time a tendency to the east, and, vice yersa, a current 

 from north to south a tendency to the west." One important 

 consequence became obvious toward the end of the nineteenth 

 century when certain mathematical relationships were worked 

 out among water density, current, and Coriolis force. In spite 

 of the mathematics involved this relationship is simple, and it 

 is the basis of a valuable indirect method of measuring cur- 

 rents that has been widely used during the past quarter cen- 

 tury. 



Whenever a stream flows in the ocean, the Coriolis effect is 

 balanced by a remarkable adjustment of the water layers. 

 Lighter water tends to accumulate on the right-hand side of 

 the stream and heavier water on the left, while the ocean sur- 

 face actually slopes upward across the stream toward the right. 

 Put into more familiar words, this means that the sea level 

 rises across the Florida Current and that the water level at Cat 

 Cay, in the Bahamas, is nearly two feet higher than at Miami. 

 Moreover, the amount of uphill that a vessel meets in an east- 

 ward crossing of these Straits is a measure of the speed of flow 

 of the Stream; and this can be calculated from the impor- 

 tant theorem of Vilhelm Bjerknes. The geostrophic relation, 

 as it is called, was a wonderful new tool for oceanographers, 



