V 



Chap. I.] INERTION. !•"> 



This is a simple law of nature :■ — though the' vessel 

 containing the water is set in motion, the water tends 

 to maintain its position, and therefore has a relative 

 motion over the surface of the vessel in the opposite 

 direction to that in which the vessel is moved. 



We need not immediately investigate the abstract 

 nature of the force which tends to cause this relative 

 motion of the water, for it is sufficient, as far as our 

 present purposes are concerned, that it is a simple 

 matter of fact that, in the case just mentioned, the 

 water has a tendency to maintain its position ; and 

 that therefore, when the vessel which contains it is 

 moved, the force which tends to hold the water in 

 that position tends also to cause it to move along the 

 surface of the vessel in the opposite direction to that 

 in which the vessel is moved ; and that this force — 

 which indisputably does exist, be its abstract nature 

 what it may — is termed vis -inertia. 



In the consideration of the forces which keep the 

 ocean in motion, we are, for the reasons given above, 

 called on to give precedence to the action of this 

 force of inertion, or vis-inertisB. 



' Secondly, by practical investigation to ascertain whether or 

 not there exist in the ocean such movements as may, in the first 

 part, be demonstrated to be the natural result of the action of vis- 

 inertise. 



' If the practical investigations show the existence of move- 

 ments in the ocean clearly according with the theoretical deduc- 

 tions, we may then, in the absence of any other reasonable cause 

 being adduced, conclude that vis-inertise is the cause of those 

 movements.' 



