238 



DEPARTMEyT OF THE ^AYAL SERVICE 



drawn up to the surface on the shore where the wind is blowing seawards will develop 

 a movement opposed to the direction of the wind, vide fig. 20. 



Fig. 20. — Current opixjsed to the wind on weather 

 shore and lee. 



In large areas, the wind cannot be regarded as a constant current of air progress- 

 ing continuously over the whole area, but rather as a series of stormy gusts extending 

 over a wide expanse. Such a storm, acting upon water in layers, produces a very large 

 submarine wave, probably hundreds of metres high, which moves slowly forward in 

 the direction of the wind, vide fig. 21. This wave is caused by the friction between 

 the current of air and the surface layer. As the wave moves forward, the surface water 

 in front of it must pass over behind the crest of the wave. A strong current, moving 

 against the wind, thus arises in the surface layer, and this will make itself apparent 

 even before the storm itself has reached the same point, thus serving as a storm warn- 

 ing. From fig. 21, it will be seen that the current flowing in a direction opposite to 

 that of the wind continues to do so for some little time after the wind has come up, 



Fig. 21.— Surface current on the approach of a storm. 



but then decreases in force. Such cui*reuts against the wind have frequently been 

 observed in Canadian waters. 



7.— INFLUENCE OF THE EARTH'S ROTATION ON THE MOVEMENTS 



OF THE WATER IN THE SEA. 



Of all the forces acting upon the sea-water, that of the earth's rotation is the 

 one which, as regards its effects, is most remarkable and difficult of comprehension. 

 It is frequently found to force light water downwards, and heavier water to the 

 surface, with the result that the distribution of density appears strange and 

 mysterious. I am inclined to believe that our inability to comprehend the effects of 

 this force is principally due to the fact that we have no senses for the direct per- 

 ception of the rotation of the earth. All our direct perceptions indicate the earth 

 as motionless. True, we have learned at school that -the earth rotates, and can also 

 more or less form an idea of its doing so, but as a matter of fact, in our daily life, 

 as in the laboratory, we are independent of such rotation. All the small phenomena 

 around us we are accustomed to view from the standpoint of an immobile earth. 

 When, therefore, in discussing the movements of the sea, the rotation of the earth is 

 seen to take a prominent place, its effects appear to us strange and inexplicable. 



A being situated somewhere outside our planet, and observing, not only the 

 phenomena taking place on the earth's surface, but also the rotation of the globe 



