450 FOURTH REPORT — 1834. 



apparent discovery, Dubuat endeavoured to render the experi- 

 ments of Bossut conformable to it, and in the year 1779 pub- 

 lished his Principes Hydraiiliques. 



Dubuat felt, however, that his theory required further elucida- 

 tion, and having undertaken a more extensive series of experi- 

 ments, published the result in three volumes in the year 1786*. 



The first two volumes treat of the uniform and variable mo- 

 tions of water in rivers, canals, and pipes ; the origin of rivers, 

 the establishment of the beds, and the effects of dams, sluices, 

 bridges, reservoirs, and fountains ; the navigation of rivers and 

 canals, and the resistance of fluids. 



The last volume treats of the mechanical properties of setherial 

 fluids as affected by heat. Dubuat had been long sensible of 

 the unsatisfactory state of the theory of the motions of rivers 

 and the difficulty which surrounded the discovery of a true 

 theory, conceiving that every river ran with an uniform velocity 

 peculiar to itself, and that the velocity in the middle was greatest. 

 He believed that the formation of bends in them was owing to 

 obstacles ; that the development of their curves was in propor- 

 tion to the mean radius : and having traced geometrically the cir- 

 cumstances of his hypothesis, he had recourse to analyses, out of 

 which he formed equations applicable to practice ; and having 

 observed frequent changes in rivers from floods and other causes, 

 he concluded, that it was easy to find the expenditureof ariver in 

 any part of its course by calculating the annual produce of the 

 rains which fall upon the surface of the surrounding country, 

 deducting a certain proportion (4th) for filtration, evaporation, 

 &c. Hence the total expenditure of a river is deduced by the 

 product of its mean section and mean velocity. The author ap- 

 plied his principles to the river Seine ; he examined different 

 cases of the expenditures of water, and added new expressions 

 for each to his formula of uniform motion ; and in the case of 

 great rivers which are difficult to submit to experiment, he as- 

 similated their motions to the motions of fluids through conduit 

 pipes. 



In commenting upon the experiments of Bossut, he says, 

 " The experiments which occasioned the greatest difficulties 

 were those on rectangular and trapezium canals, in as much as it 

 was found very difficult to render the motion of the current uni- 

 form ; but we have been amply recompensed by the experiment 

 which we had occasion to make on the diminution of the velocity 



* Principes d' Hydraulique verifies par un grand nomhre ^Experiences faites 

 par Ordre du Gotivernement ; Ouvrage dans lequel on traite du Mouvement uni- 

 forme et varie de I'Eau dans les Rivieres, les Canaux, ef les Tuyaux de Con- 

 duite, ^-c. : par M. le Chevalier Du Buat 



