422 FOURTH REPORT — 1834. 



according to tlie law represented by the coordinates of a funi- 

 cular curve, by which the upper part of the canal had an inclina- 

 tion of 0'"-0000625 per metre, and the lower part of 0™-0001236 

 per metre ; but these inclinations wei*e found insufficient. M. Ge- 

 nieys prefers one decimetre per kilometre, or j^nijo* Dubuat 

 is inclined to think that the smallest inclination capable of main- 

 taining the mobility of water is t^oFoooj b"* ^^^* ^^ JlJiroo o 

 it is barely perceptible ; and in an artificial channel set to ^g^K 

 he found the mean velocity to be nearly 6 inches per second, and 

 7 inches per second in a drain near Conde, of which the inclina- 

 tion was 2 7^0 0, and 10 inches per second in the river Hayne, with 

 an inclination of -^-j^oq'*. M. Bossut found the motion to cease 

 entirely with pipes having less inclinations than those of Dubuat. 



M. Dubuat has given the results of seventeen experiments on 

 the mean and superficial velocities and radius of a trapezium 

 canal set at inclinations of 2x2 to ^^^, also the same results from 

 fifteen experiments made in a rectangular canal set at inclina- 

 tions of from ^j^ to 27^^^^, also of four experiments on the 

 superficial and mean velocities of the river Hayne, all of which 

 he finds to accord with very nearly the theory laid down by him. 



The Romans inclined their canals much more than the mo- 

 derns. Vitruvius fixed the inclination at g^^, Scamozzi at j^-q. 



From diffei'ent observations made on the ancient aqueducts by 

 M. Rondeletf, he found the mean inclination to be 1^ line per 

 French toise, or about -^jq, towards the lower part, li line, or 

 y|^, towards the upper part. More recent experiments have 

 made the inclination from -^^-^ to j-^-^. 



According to M. Prony, the following are some of the inclina- 

 tions of the canals and rivers of the Pontine Marshes. 



„ Low Water. High Water. 



Canal of Pius VI., in two ""''"'• '] Metres. Metres. 



lengths of 17^677 4-811000 4-603000 



Inclination in unity of the length . . . . > 0-000272 0-000260 



Second length 9,112 ( 0-619000 1-830000 



Inclination in unity of surface .... J 0-000068 0-000091 



• The drains in Lincolnshire are inclined at 5 inches to a mile, or ttttt' 

 The slope of the New River is 3 inches per mile, or -j-rhnr- The slope of the 

 Eau Brink Cnt in Norfolk is 5 inches per mile. The slope of the New Cut of 

 the Nene at Cross Keys Wash, in Lincolnshire, is about 4*9 inches per mile. 



Of the inclinations of the Caer and Foss Dykes, originally constructed by the 

 Romans, we have no positive information ; but from -ro-o-iro- to r joo Tr seems to be 

 a fair average for the inclinations of the drains in low countries ; and on straight 

 canals, such as the Thames and Medway, we have seen the effects of the wind 

 in raising the surface higher at one extremity than the other equal to 1^ inch 

 per mile. 



t See Commentaire de Frontinus stir les Aqueducs de Rome, par Rondclet : 

 Paris, 1820. 



