CuAP. XII.] OCEAN CURRENTS. 147 



to be exemplified by the Arctic stream, which runs 

 southwards on the North American coast, thrusting 

 the Gulf Stream farther from the coast in March than 

 in September. These currents have been more elabo- 

 rately investigated than any other great ocean currents, 

 and the annual variation here mentioned accords 

 with the idea of its being influenced by the earth's 

 orbital motion ; but I have not met with any other 

 recorded variations of ocean currents that appear suffi- 

 ciently definite to be adduced as indicating the action 

 of the same cause. 



As regards the diurnal variation which, if the 

 line of motion be not coincident with the line of the 

 poles, must result from the action of vis-inertia3 

 being west of north in the night-time and east of 

 north in the daytime ; — the phenomena of winds in 

 given localities having a different average direction 

 in the night-time from the average direction in the 

 daytime are in accordance with such a cause ; though 

 I know of no recorded phenomena that can be clearly 

 traced in its action, as alterations in the relative 

 temperature on land and water tend to produce the 

 same effect. The Straits of Gibraltar appear well 

 adapted for ascertaining the diurnal variation in the 

 orbital force of vis-inertite, as the tendency of its 

 action would be to cause a current westwards from 

 the Mediterranean in the night-time, and eastwards 

 from the Atlantic in the daytime ; and therefore the 

 current may be expected oftener to take a westward 



