126 



Prof. J. Thomson on the Flow of Water. [Dec. 12, 



two artificially-formed channels on the Ganges Canal, one of them, 

 168 feet wide, and the other 85 feet wide, and each having the water 

 often about from 6 feet to 9 feet deep, he states (p. 46, article 35): 

 " There is a constant surface motion (deviation) from the edges 

 towards the centre, most intense at the edges and rapidly decreasing 

 with distance from the edges." 



This experimental conclusion, on the supposition of its being 

 decidedly trustworthy, as Mr. Cunningham asserts with confidence 

 that it is, I think may probably be satisfactorily explicable through 

 considerations intimately connected with those which I have already 

 given for an amended theory of the flow of water in rivers. 



I wish, however, not to prolong the present paper by entering on 

 any detailed discussion of this branch of the subject, and besides I 

 prefer to reserve this for some further consideration before venturing 

 to put forward the views in reference to it which at present appear to 

 me likely to be tenable. It may be noticed, however, that Captain 

 Cunningham's experimental result, if decidedly correct, throws addi- 

 tional light on the subject of the abatement of surface velocity compa- 

 ratively to the velocity at some depth below the surface being found 

 in Bazin's experiments to occur in a much greater degree near the 

 sides of rectangular and various other channels than at middle. Bazin 

 thought indeed from his own experiments (as I have already had occa- 

 sion to mention) that the relative retardation or slowness of the 

 surface occurred not in the middle of wide channels (that is to say, of 

 channels wide relatively to the depth of the water) but only near 

 the sides ; but this supposition I have referred to as appearing not to 

 be trustworthy. With these brief suggestions I will now leave for 

 further consideration the subject of the special phenomena of the 

 influence of the sides. 



Historical Note. 



Subsequently to my having formed, in all its primary or more 

 essential features, the new view now explained of the flow of water in 

 rivers, and before I had met with the book of Humphreys and Abbot, 

 I happened to see in the writings of another author (paper of 

 Mr. Gordon already referred to) the following remark in reference to 

 their views as to the velocity at the surface being less than at some 

 depth below. " Humphreys and Abbot attribute the fact to trans- 

 mitted motion from the irregularities of the bottom ; but confess them- 

 selves dissatisfied with their own explanation." 



These words seemed to me to indicate a probability of Humphreys 

 and Abbot having anticipated me in some part at least of the 

 theory which I had been forming. On obtaining their book, how- 

 ever, and reading the passage referred to, not by itself alone, but with 

 its context, it appeared to me that it involved no real anticipation, 



