CANADIAN FISHERIES EXPEDITION, 19U-15 279 



The earth's rotation, however, also exerts a certain influence upon the circulation 

 of the water. When the solenoids have set the water in motion, it is forced over to the 

 right by the rotation of the earth. This pressure is augmented as the velocity of the 

 water increases. Consequently, the rapidly moving surface water in a current is urged 

 more forcibly to the right than the slower-moving water at greater depths, so that the 

 total movement of the water mass will be a screwing one. And a transverse section 

 across the current will therefore reveal a circulation taking place within the same. For 

 this, the acceleration of circulation will be 



d(J dS 



= 2 w 



dt ^ dt 



This circulation is itself opposed by the friction, wherefore 



dt dt 



As the circulation is increased, the opposing force of the friction will likewise be aug- 

 mented, until the influence of the latter will attain a magnitude equal to that of the 



d C 

 earth's rotation. Then ' , will disappear, and the circulation become stationary. 



dt 



If the water of the current be in stable layers, then a system of solenoids will arise 

 in the section across the same, and will, like the friction, oppose the influence of circu- 

 lation occasioned by the earth's rotation. In this case, then, 



dC dS , „ 



dt "" dt 



Where the water is very stable, these reactionary solenoids may altogether arrest 

 the circulation in the cross section. Then R will also disappear, and we have 



dC dS 



= %> —rr- — ^ 



dt '" dt 



The number of solenoids increases until it attains the same value as the influence of 



d 

 the earth's rotation, whereby——— disappears, and a stationary situation sets in. It 



d t 



is on such a state of things that rates XIV and XV have been based. 



d C 



In all the cases here described, the acceleration of circulation — increases 



d t 



rapidly at first from its value nil when the sea is at rest, reaches a maximum, and then 

 declines asymptotically towards nil, when stationary conditions are reached. Fig 55a 



d C 



shows this variation of in course of time. 



d t 



If the physical change in the water which gave rise to the current be of temporary 

 nature, then the number of solenoids thus produced will gradually decrease, the current 

 meanwhile progressing by inertia. The eft'ect of friction will then be superior to that 



d C 

 of the solenoids, and-^r- will be negative. As the physical changes gradually cease, 



d t 



the final state will in this case be that of calm and equilibrium. Fig. 55b shows the 

 variation in the acceleration of circulation fox a casual and temporary current oi this 

 nature. 



