1878.] Uniform Regime in Rivers and other Open Channels. 119 



Quite recently, in 1874-75, experiments were conducted in India on the 

 Ganges Canal, close to Roorkee, by Captain Allan Cunningham, R.E.* 

 These experiments bring out among their results, very remarkably, 

 the frequently alleged phenomenon of the maximum velocity of the 

 water being not at the surface, but at some moderate depth below. 

 And further, it is deserving of special notice that those of his experi- 

 ments, which have chiefly to be referred to as throwing light on this 

 subject, were made in an aqueduct about 85 feet wide, and with an 

 approximately level bottom ; and that the depths of the water in 

 different experiments ranged from about 6 feet to about 9-J feet, so 

 that the width was on different occasions from about nine times to 

 about fourteen times the depth, and yet the maximum of the velocities 

 at mid-channel (or the maximum velocity in the longitudinal medial 

 vertical section) came out by averages of numerous results, and, by 

 varied modes of experimenting, to be very decidedly below the sur- 

 face. 



Experiments carried out lately on a very large scale on the Irawaddy 

 river by Robert Gordon, Executive Engineer, British Burmah, Public 

 Works Department, go to confirm the truth of the same phenomenon. 

 These experiments of Mr. Gordon, however, although valuable in many 

 respects, appear to be subject to some doubt as to whether, through 

 the mode of experimenting, the level of supposed maximum velocity 

 has not been brought out too low, that is to say, too near the bottom. 

 On this point Mr.. Gordon (in his Introductory Note, § vii, page ii of 

 date 16th June, 1875) intimates his intention to make further experi- 

 ments with other instruments, but still asserts his confidence in his 

 previous methods and results. 



Until about two years ago I had not happened to become acquainted 

 with any of the evidence for the phenomenon in question except the 

 unsatisfying experimental results given by Ellet ; but about two years 

 ago I met with accounts of some of the more recent and more convinc- 

 ing experimental investigations. It then appeared to me that if the 

 asserted phenomenon must really be accepted as a truth, there ought 

 to be some mode possible of accounting for it : and a theory occurred 

 to me which I now propose to submit. 



The mode of thought which near the beginning of the present paper 

 I have described as constituting the laminar theory, 1 must premise, 

 has long appeared to me to be an erroneous and a very misleading 

 view. It was a very prevalent mode of thought, and was usually too 

 influential on people's minds even when they did entertain decidedly, 

 though often not clearly enough, the consideration of eddies and trans- 

 verse movements or commingling currents with different velocities. 



* " Hydraulic Experiments at Roorkee, 1874-75," by Captain Allan Cunning- 

 ham, R.E., published in " Professional Papers on Indian Engineering." Thomason, 

 College Press, Roorkee, 1875 : also Spon and Co., London, &c. 



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