between High-water and Slack-water, 1^7^; 



modified of course by the quantity of fresh water in ordinary 

 rivers. 



That this is the true theory of the interval between high-water 

 and slack-water, may also be inferred in a simpler manner from 

 the following considerations. Let an observer station himself 

 at any point in a tidal river, say at Putney Bridge, just before 

 high-water : the tide will then be flowing up strongly in the 

 middle of the river, slowly along the shore (see below) ; at high- 

 water it will cease flowing along the shore and rise no higher, 

 and in a short time will begin to fall, but will still run up in the 

 middle. Now we know that high-water at Richmond and other 

 places will not take place for more than an hour after high-water 

 at Putney, and that the level of the water at Richmond is at this 

 time lower than at Putney. But where is the water to come 

 from which makes high- water at Richmond ? obviously it must 

 come from below through Putney Bridge : and it is the water 

 flowing up to make high-water at Richmond which causes the 

 middle of the river to continue flowing at Putney after high- 

 water ; and when a sufiicient quantity of water has flowed to 

 make the level at Richmond as high or a little higher than 

 at Putney, the tide will turn at Putney. 



Explanation of the turn of tide near the shore before it turns in 



the offing. 



Let us now suppose an obstacle OB in the channel C, then 

 whilst the tide is flowing, the water in OBM will not run with 

 the same velocity as that in the main channel, but will merely 

 have the velocity necessary to bring sufficient water into OBM, 

 so that the water in OBM may continue to rise with the rise of 

 tide. Now when the tide has ceased to rise, the water in OBM 

 will cease to run at all, though, as before shown, the water in C 

 will continue to flow : and when the tide begins to fall, the 

 water in OBM will ebb (with the velocity necessary to take the 

 water out of OBM, at such a rate as that the water in OBM 

 may fall with the fall of tide), though the water in C will still 

 continue to flow. It is obvious that OBM is a representation 

 of the ordinary slack-water along the margin of rivers, occasioned 

 either by actual projections or by the friction of the shore and 

 shoals, or by the set of tide. 



I add a few observations taken by me at Putney on a very 

 calm afternoon, 9th of Nov. 1851, when there were many leaves, 

 &c. floating on the stream. There was nothing particularly 

 remarkable in the tide, but I am not aware that a similar 

 set of observations are to be found in print, and the study 

 of a tide of this sort may be instructive. 



