22 THE OCEAI?, [Book II. 



southwards. This divergence from the equator im- 

 plies a change of latitude : therefore a tendency to 

 cause a change of latitude is an attribute of west- 

 ward pressure. 



And change of latitude has itself two important 

 attributes whose action in the atmosphere was clearly- 

 recognised by George Hadley as affecting the course 

 of the Trade Winds ; but whose action in the ocean 

 appears to have been first pointed out by Captain 

 Maury, as affecting the course of the Gulf Stream : 

 that is, that a tendency to change of meridian east- 

 wards is an attribute of such change of latitude 

 as causes an increase of equatorial distance ; and 

 that a tendency to change of meridian westwards 

 is an attribute of such change of latitude as causes 

 a decrease of equatorial distance. 



For, since the velocity with which the surface of 

 the earth rotates at the equator is upwards of a 

 thousand miles an hour and at the poles nothing, 

 therefore, in any change of latitude in a direction 

 leading from the equator towards either of the poles, 

 that which changes its latitude has a faster eastward 

 momentum than that which belongs to the latitude 

 into which it enters, and will consequently have a 

 tendency to change its meridian eastwards. Whereas 

 in any change of latitude in a direction leading from 

 the poles towards the equator, that which changes 

 its latitude has not so fast an eastward momentum 

 as that which belongs to the latitude into which it 



