REPORT ON HYDRAULICS. — PART II. 449 



inclined pass off a greater quantity of water than horizontal 

 canals : this is illustrated by a great many experiments on the 

 velocities of water issuing from openings under variable and in- 

 variable pressures and inclinations of from three inches to eleven 

 feet. 



. The experiments were repeated upon a larger scale in a canal 

 of 600 feet in length, and with nearly similar results, namely, 

 that the velocity augmented with the inclination. There were, 

 however, observed two distinct velocities, viz., the velocity of 

 projection as the fluid issued from the orifices, and the invariable 

 velocity which established itself inequilibrio with the resistances. 

 When the canal had scarcely any inclination below a tenth part 

 of its length, there existed little or no uniformity between the 

 primitive and permanent velocity. M. Bossut attempts to make 

 several applications of his experiments to rivers ; among others, 

 to the Beuvronne, which he found to have an inclination of 

 j-jj'o (J nearly, the same as the Seine at Paris*, although the 

 velocity of the Beuvronne, as compared with the velocity of the 

 Seine, was as 36 to 100, and the quantity of water passed 

 through the respective sections was as 1 to 278 ; from which he 

 deduced that with equal inclinations the gi-eatest quantities of 

 water have the greatest velocities, but that the velocities do not 

 augment in the ratio of the quantities of water ; hence the 

 reason, according to him, that when two rivers unite into one, 

 the capacity of the channel of the united river is always less than 

 the sum of the capacities of the minor rivers taken conjointly : 

 these minor rivers may also have different inclinations and velo- 

 cities than the united river. He differs in some respect from 

 the principles of Gennete, but agrees with him in the inutility 

 of derivations from rivers, and very properly refers to M. Du- 

 buat for more precise information on the subject. 



Inspired by the perusal of Bossut's work, Dubuat endeavoured 

 to investigate the subject de novo, by considering, that if water 

 was perfectly fluid, and received no impediment from the surface 

 over which it moved, it would be accelerated in the same man- 

 ner as bodies running down inclined planes ; but as this effect 

 was found not to take place, he concluded that there existed a 

 certain degree of retardation arising from the friction of the 

 channel or the viscosity of the water, and that when water ran 

 uniformly in any channel whatever, the accelerating force was 

 equal to the sum of the resistances. This principle, as we have 

 seen, had been long known in Italy. Encouraged by this 



* According to later observations the inclination of the Seine varies from 

 1834. 2 G 



