200 OUTLINES OF NATURAL PHILOSOPHY. 



rived immediately from experiment. BOSSUT, torn. n. 

 647, 648. At 673. he has given a table of the 

 actual discharges of water-pipes, as far as the length 

 of 2340 toises, or 14950 feet English. 



291. Water running in open canals, or in rivers, 

 is accelerated in consequence of its depth, and of the 

 declivity on which it runs, till the resistance, increa- 

 sing with the velocity, become equal to the accele- 

 ration, when the motion of the stream becomes uni- 

 form. 



It is evident, that the amount of the resisting forces 

 can hardly be determined by principles already 

 known, and therefore nothing remains, but to as- 

 certain by experiment, the velocity corresponding to 

 different declivities, and different depths of water, 

 and to* try, by multiplying and extending these ex- 

 periments, to find out the law which is common to 

 them all. 



The Chevalier Du BUAT has been successful in this re- 

 search, and has given a formula for computing the 

 velocity of running water, whether in close pipes, 

 open canals, or rivers, which, though it may be call- 

 ed empirical, is extremely useful in practice. Prin- 

 cipes ffHydr antique, par M. LE CHEVALIER Du 

 BUAT, 2 vol. 8vo. edit. %. Paris 1786. Professor 

 ROEISON has given an abridged account of this book, 

 in his excellent articles on Rivers and Water-works, 

 in the Encyclopedia Britannica. 



Let V be the velocity of the stream measured Ipy the 

 inches it moves over in a second; R a constant 



quantity, 



