114 On Moseley's Theory of Shady Flow. 



A few selected instances from the Eoorkee experiments*, 

 with widely differing data (as to width, depth, velocity, and 

 discharge), are given in the table below. 



Data. Value of Discharge- 



Site. ., so B, measurement 



B. I E. v t , 0d ° B °' D. 



4 



Solani left aqueduct 10O: 



Solani right aqueduct 105'8 



Solani embankment, main site... 190-8 



Fifteenth mile, new site 1820 



Belra site 1964 1 902 367 430 5011 



Jaolisite 200-21 7"82 3-43 473 4631 



Kanihera site 09-51 4"84 340 263 901 



6-75 4-05 324 S-}2< 



7-96 4-52 323 3429 



934 400 512 7169 



949 4-91 507 7187 



It will be seen that the computed values of 



B 



which should he all greater than the discharge-measurements 

 (D), are actually only from about £ to -^ of the latter; so that 

 the formula is evidently useless for application to large bodies 

 of water. 



The Eoorkee experiments also furnishf important (nega- 

 tive) evidence on the vexed question of the supposed convexity 

 of the water-surface in an open channel. Canon Moseley states 

 (in the same essay f) that, as a result of theory, — 



" As the pressure is everywhere less where the velocity is greater. 

 it is evident that there will be a tendency in the liquid on the 

 surface to flow from the sides of the channel towards the 

 centre, and that thus the velocity of the surface-water at the 

 centre will be diminished, and the water heaped up, drowning, 

 as it were, the point of greatest velocity in the section." 



Xow two of the results above indicated — viz. the constant 

 transference of surface-water § from the edges towards the 

 centre and the depression || of the maximum velocity below the 

 surface — have been amply Aerified experimentally. But as to 

 the " heaping-up " of the surface-water at the centre, or, in 

 other words, as to the surface-convexity (the existence of which 

 seems to be accepted by writers on hydraulics), the author has 

 not been able to find any certain experimental evidence, i^ome 

 special experiments were accordingly made by him to test the 

 point, at a site extremely favourable for the trial, in a canal of 

 about 170' surface-width and 11' depth, with a central sur- 



* Eoorkee Hydraulic Experiment-, vol. i. p. 207. 



t Op. cit. vol. i. chap, vm* passim. 



X Philosophical Magaziue, [4] vol. rdiv. p. 44. 



§ Eoorkee Hydraulic Experiments, vol. l. chap. rvii. arts. 14-14 6. 



II Op. cit. vol. i. chap. xii. passim. 





