466 Of dilatory Motion of Water [B ook V 1 1 . 



ef y in the branch /#; as foon as this caufe ceafes to 

 act, the fluid will be operated upon merely by the 

 common laws of gravitation and motion. The excefs 

 of the length of the column e n y above that of the co- 

 lumn b o, will force the fluid to defcend, and that even 

 below the level of the other, on account of the accele- 

 ration of its defcent, which will caufe the fluid in the 

 other branch m o to rife ; the fluid will then defcend 

 and afcend alternately, or in ofcillations fimilar to thofe 

 of a pendulum; and the deviation of each of thefe 

 ofcillations will be precifely the fame as that of the 

 ofcillations of a pendulum half as long as ^ie length 

 f q r of the column of the fluid. 



Since the ofcillations of wafcer follow the fame law 

 as thofe of a pendulum, it follows, that if the length of 

 the column of water is augmented or diminifhed, the 

 duration of each ofcillation will be augmented or di- 

 miniflied. ,, 



VII. The ofcillatory motion of water in waves has 

 been compared by Sir Ifaac Newton * to the ofcilla- 

 tory motion of water in a fiphon. 



Let A B C D E F (Fig. 3.) be fuppofed a meet of 

 water, the furface of which rifes and falls in fucceflive 

 waves j let A C E be the tops of thefe waves, and 

 B D F the intermediate hollows or concavities, which 

 feparate them. As the waves are formed by the fuc- 

 cefllve afcent and defcent of the water in fuch a man- 

 ner that the higher parts become the lower, and fo al- 

 ternately and fucceflively, and as the weight of the 

 elevated water is the moving power which caufes the 

 loweft parts to afcend and the higheft to defcend, thefe 

 alternate rifings and fallings are confidered as ana- 



* Priucipia, lib. I. prop. 46* 



logous 



