CnAP. II. J INERTIOX. 35 



the circles of rotation in the direction in which the 

 axes are inclined. And, since this inclination of 

 the axes is from west at the bottom of the ocean 

 to east at the surface ; therefore, the elongation of 

 the circles of rotation is westwards from the axes 

 at the surface of the ocean, and eastwards from the 

 axes at the bottom of the ocean. And thus, instead 

 of the circles of rotation resulting from either the 

 horizontal or the vertical forces, their combined action 

 causes the revolving currents enclosing each district 

 to tend to describe ellipses of rotation. 



It thus appears that, setting aside the contortions 

 caused by coast-lines, the combined action of the 

 forces of vertical and horizontal circulation gives 

 the currents which encircle each district a natural 

 tendency to revolve in elliptical courses. 



Section IV. — Surface Currents within the Districts. 



Let US now consider how the combined action of 

 these forces will affect the surface currents contained 

 w^ithin each district. 



Let NWSE, in Plate IX., figure 2, be a north 

 equatorial district. 



Under the sole influence of the horizontal circu- 

 lation, the currents would all simply describe con- 

 centric circles of rotation round a central axis. 



And, under the sole influence of the vertical cir- 

 culation, the entire surface of the district would 

 consist solely of currents running in parallel lines 



1)2 



