172 THIRD REPORT — 1833. ' 



and, assuming the hydraulicmean depth to be doubled at the 

 time of the inundation, the velocity will be increased in the 

 ratio of 7 to 5 ; but the inclination of the surface is probably 

 increased also, and consequently produces a further velocity of 

 from 1*4 to I'T. M. Eytelwein agrees with Gennete*, that a 

 river may absorb the whole of the water of another river equal 

 in magnitude to itself, without producing any sensible elevation 

 in its surface. This apparent paradox Gennete pretends to 

 prove by experiments, from observing that the Danube absorbs 

 the Inn, and the Rhine the Mayne rivers ; but the author evi- 

 dently has not attended to the fact, as may be witnessed in the 

 junction of rivers in marshes and fenny countries, — the various 

 rivers which run through the Pontine and other marshes in 

 Italy, and in Cambridgeshire and Lincolnshire in this country : 

 hence the familiar expression of the waters being overridden is 

 founded in facts continually observed in these districts. We 

 have also the experiments of Brunings in the Architecture Hy- 

 drauUque Generate de Wiebeking, Wattmann's M4moires sur 

 VArt de constriiire les Canaiix, and Funk Sur V Architecture 

 Hydraidique generale, which are sufficient to determine the 

 coefficients under different circumstances, from velocities of 

 fths to 7| feet, and of transverse sections from -l to 19135 

 square feet. The experiments of Dubuat were made on the 

 canal of Jard and the river Hayne ; those of Brunings in the 

 Rhine, the Waal and Ifrel ; and those of Wattmann in the 

 drains near Cuxhaven. 



M. Eytelwein's paper contains formulae for the contraction 

 of fluid veins through orifices f , and the resistances of fluids 

 passing through pipes and beds of canals and rivers, according 

 to the experiments of Couplet, Michelotti, Bossut, Venturi, 

 Dubuat, Wattmann, Brunings, Funk and Bidone. 



In the ninth chapter of the Handbuch, the author has en- 

 deavoured to simplify, nearly in the same manner as the motion 

 of rivers, the theory of the motion of water in pipes, observing 

 that the head of water may be divided into two parts, one to 

 produce velocity, the other to overcome the friction ; and that 

 the height must be as the length and circumference of the sec- 

 tion of the pipe directly, or as the diameter, — and inversely as 

 the area of the section, or as the square of the diameter. 



* Experiences sur le Cours des Fleuves, ou Lettre a un Magistral HoUandais, 

 par M. Gennete. Paris 1760. 



+ " Recherches sur le Mouvement de I'Eau, en ayant egard a la Contraction 

 qui a lieu au Passage par divers Orifices, et a la Resistance qui retard le Mouve- 

 ment, le long des Parois des Vases ; par M. Eytelwein,"— 3/e»io»>e« de I'Aca- 

 dimie de Berlin, 1814 and IS 15. 



