PLACE OF HIGH WATER IN EQUATORIAL CANAL. 5 



^each portion of water is moving faster than that just in 

 advance of it ; or, in other words, where water is flowing in 

 faster than it flows out. Where this process has gone on 

 for the maximum time the tide will be highest. On the 

 other hand, the tide will be falling where the water is 

 moving slower than that in advance of it or, in other 

 words, is flowing out faster than it flows in. Where this 

 has continued for the maximum time the tide is lowest. 



Now consider any point s in the quadrant BC. The 

 water now passing s has been subject to an accelerating 

 force during the whole time since it passed B, longer 

 therefore than any particles behind it, as at r. It is there- 

 fore moving faster ; and as the water in the space r s is 

 thus flowing out faster than it flows in, the tide is falling. 

 This is the case through the whole quadrant BC. 



At C the force changes and becomes a retarding force. 

 The particle at y has been subject to this retarding force 

 longer than one behind it, as at #, and is therefore moving 

 slower. Here, therefore, water is flowing in faster than it 

 flows out, and the tide is rising ; and this holds through 

 the quadrant CD. What is said of these quadrants holds 

 also of those opposite to them ; the tide is falling all 

 through DA and rising through AB. Hence it is highest 

 at B and D, lowest at A and C. Where will the tide be 

 falling fastest ? Clearly where the difference of velocity 

 between r and s is greatest, i.e. where the amount of force 

 to which the water at s has been subject since it passed r 

 is greatest in other words, where the force is at its 

 maximum, viz. at / (fig. 3), 45 from C. Similarly it 

 will be rising fastest at that point in the quadrant CD 

 where the force is greatest, viz. at ff, 45 from C. 



