REPORT OX HYDRAULICS. PART 11. 451 



of a uniform current, reckoning from the surface to the bottom, 

 and by very curious observations on the mode in which the 

 water corrodes the bottom, according to the kinds of soil, such 

 as gravel, sand, and clay, which constitute it." 



After recapitulating the various principles laid down in his 

 first edition relative to the effect of bridges, sluices, aque- 

 ducts, &c., he develops the fundamental principles of uni- 

 form motion, the causes which create, and the resistances which 

 affect it, which latter he makes proportional to the squares of the 

 velocities ; he gives a formula for uniform motion in any channel, 

 and then shows by experiment and by analyses the causes of va- 

 riation, what amount is due to friction, and what to adhesion or 

 viscosity. By this means the law of motion is developed from 

 infinite velocities to its total cessation. These elements deter- 

 mined, he examines the nature of the different beds over which 

 rivers run, whether natural or artificial ; the effects of floods or 

 the affluents of rivers, shortenings, swellings, derivations ; the 

 forms most proper for canals, the piers of bridges ; and illustrates 

 the whole by a great variety of experiments, which are extended 

 to the resistance of fluids. 



Dubuat values the effect of viscosity at 0*3 of an inch : 

 the mobility of water he limits to iq^oqo of the inclination, and 

 considers 50^060 ^o be the smallest possible inclination that can 

 be given to a canal to produce sensible motion. He cites several 

 experiments made by him on an artificial canal with an inclina- 

 tion of ^gV^ which gave only a velocity of 6 inches per second, 

 whilst in a drainage canal with an inclination of gf 006 ^^^ velocity 

 was only 7 inches per second, and in a part of the river Hayne 

 having an inclination of 33^ the velocity was 10 inches per se- 

 cond, so that the velocity was greatest with the least inclination. 

 Dubuat adds, " it is impossible to reason against facts." The 

 anomalies which prevail throughout the whole of Dubuat' s work 

 render many of his conclusions very doubtful. The principles 

 upon which Dubuat founds his theory of uniform motion ai*e : 



Istly, That water is composed of molecules perfectly spherical, 

 hard, and polished, but gifted with a certain degree of tenacity ; 



2ndly, That rivers cannot run without a certain degree of in- 

 clination in their surface ; 



3rdly, That when the mean velocity of a river is uniform, the 

 accelerating force is equal to the resistance of the bed ; 



4thly, That it is the tendency of every mass of water to form 

 its own bed by filling up the inequalities of the bed itself ; 



5thly, That the surface of this bed consists of an assemblage 

 of molecules or globules, over which the other globules glide, 



2g 2 



