432 



ILLUSTRATIONS OF THE 



380. But if the attentive fpedlator, inftead of* 

 tmlting to a vague impreflion, or liilening to 

 fome crude theory of undulations, refleds on 

 one of the mofl fimple fads refpeding the ebb- 

 ing and flowing of the tides, he will be very 

 little difpofed to acquiefce in the above conclu- 

 fion. He has only to confider, that the flowing 

 of the tide requires jufl: fix hours, and the ebb- 

 ing of it likewife fix hours; fo that the fame 



body of 



fl 



upon the fliore, and 



of matter 



with 

 fame 



from it, in the fame time. The quantity 



d, therefore, and the velocity 



are in both cafes the 



I 



• Mr Kirwan to (hew 



hich it is moved 



and it 



m 



fo 



in what the difference of their force can pofli 

 biy coniift. 



The force with which the waves ufually brea 



•■a 



upon our fh 



docs not arife from the velo- 



•eater in one diredion 



city of the tide being greater 

 than in another. In the main ocean, the waves 

 have no progreflive motion, and the columns of 

 water alternately rife and fall, without any other 

 than a reciprocating motion: a kind of equilibri- 

 um takes place among the undulations, and each 

 wave being equally aded upon by thofe on op- 

 pofite fides, remains fixed in its place. Near 

 the fhore this cannot happen ; the water on the 



land fide from its fliallownefs being incapable 



of 



