REPORT ON HYDRAULICS. — PART II, 461 



Gthly, That the experiments of Dubuat with pipes and chan- 

 nels composed of different substances are in accordance with 

 this doctrine ; 



7thly, That the adhesion or cohesion of the particles of the 

 fluid to each other, and to the surface of the pipe^ require to be 

 represented by different values, capable of being compared with 

 each other. 



The remainder of M. Prony's physico-mathematical researches 

 is devoted to the examination and determination of the general 

 relations which subsist between the longitudinal and transverse 

 sections to the perimeters, and the velocity of the water under 

 the influence of friction and viscosity ; the whole is illustrated 

 by tables and formulae derived from numerous experiments by 

 Couplet, Bossut, Dubuat and Chezy. 



The corps of engineers of roads and bridges of France have 

 contributed largely to our knowledge of the theory of rivers, and 

 the numerous experiments which have been undertaken by dif- 

 ferent engineers of that body have confirmed in a great degree 

 the theories advanced by preceding writers. The experiments 

 which merit the most attention are those of MM. Raucourt and 

 De Fontaine ; the former on the river Neva at St, Petersburgh, 

 and the latter on the river Rhine. 



The object of M. Raucourt's experiments was to ascertain 

 how far the law of the velocities coincided with the theory of the 

 motions of water in pipes and open channels when the river was 

 frozen, and when free from ice. 



Accordingly, he embraced the opportunity of the Neva being 

 frozen over in the year 1824; and having selected a place where 

 the width of the river is 900 feet, and the greatest depth 63 feet, 

 and the section very regular, and consequently assimilated to the 

 case of an immense pipe, he provided an instrument, constructed 

 on the principle of the connuon ship's log, and ascertained the 

 velocities by sinking the instrument through several holes made 

 in the ice at proper intervals : the maximum velocity was found 

 to be a little below the centre of each vertical, and diminished 

 as it approached either bank of the river. The same relative 

 velocities, differing only ^th from each other, were found to 

 prevail after repeated trials. The results were, that the greatest 

 velocity was found to be a little below the centre of the deepest 

 vertical : 



ft. ins. 

 viz. 2 7 per second. 



Ill ditto .... near the top. 

 1 8 ditto .... near the bottom. 



In the summer of the year 1826 M. Raucourt performed 



