26 THE OCEAN. [Book II. 



sequence of the decrease in the circumference of the 

 earth in the latitudes which they are simultaneously 

 entering, ^^ow, as far as the forces at present under 

 consideration are concerned, there is no reason why 

 the stream on any one meridian should yield rather 

 than that on any other meridian ; and therefore, the 

 only manner in which the course from the equator 

 could be continued would be by an increase in either 

 the depth or the velocity of the strata in inverse 

 proportion to the decrease in the circumferences of 

 the consecutive latitudes. But gravitation will 

 obviously prevent an increase of depth more than 

 sufficient to carry the streams onwards a moderate 

 distance beyond the latitude at which compression 

 commences ; and that tendency to run eastwards, 

 which increases in proportion with any increase of 

 velocity, will just as obviously prevent the increase 

 in the velocity of their course from the equator 

 which would be necessary to carry the whole volume 

 of the streams onwards towards the poles. And 

 therefore, since there cannot be either an increase of 

 depth, or an increase of velocity sufficient to carry 

 the streams onwards towards the poles, and since the 

 stream on any one meridian will not yield to allow 

 of that on any other meridian proceeding, the pole- 

 ward course of the upper strata must cease equally 

 on every meridian. The streams of the upper strata 

 must gradually descend on every meridian into the 

 lower strata, where, on reaching the surface of the 



