6 



THE TIDES. 



On the whole, then, the water in the supposed equatorial 

 canal assumes the form of an ellipse ; and as it is the earth 

 that is rotating, this ellipse does not change its absolute 

 position except with the moon's motion ; only the water 

 accompanying the rotating earth moves fastest at A and 



(7, and is there lowest; and slowest at B and D, and 

 is there highest. Relatively to the earth it is moving 

 westward from e to /and from g to h ; eastward from /to 

 g and from h to e. At A, J9, (7, D, the particles are in 

 their mean places ; at ,/, g, h, they are farthest from their 

 mean places, and change the direction of their relative 

 motion. This is represented in fig. 3, where the inside 



BD 



AC 



Fig. 4. 



arrows show the direction of the earth's motion ; the out- 

 side arrows that of the relative motion of the water. The 

 path of any one particle may be represented by fig. 4, 

 where the letter A indicates the position of the particle 

 when its mean place is at A in fig. 3. 



