47 



CHAPTER III. 



EFFECTS OF THE EARTH's ONWARD MOTION. 



PART I. 



EFFECTS OF ORBITAL MOTION. 



According to the foregoing the action of vis-inertia? 

 in causing currents results from inequality of oppos- 

 ing forces ; and therefore, as regards the orbital 

 motion of the earth, since its velocity is the same at 

 all parts of the earth, it is obvious that its action in 

 causing currents can result only from the greater 

 facility with which water yields to the action of vis- 

 inertiffi in one part of the ocean than in another part. 

 And, that the water tends to yield more readily in 

 some parts of the ocean than in others to the action 

 of any force which may tend to set it in motion, may 

 be illustrated by the well-known phenomenon that 

 in any river or stream the water at the surface of 

 the deep and central parts tends to move more 

 rapidly than that in shore or at the bottom of the 

 stream ; because the friction of the ground over 

 which it runs checks the progress of the water, 

 leaving that at the surface of the deep and central 

 parts of the stream comparatively free to run its 



