274 Archdeacon Pratt on the [No. 3, 



i rom the preceding theory, regarding the late flood — much local 

 knowleclge would be requisite to obtain any result which would be 

 even generally satisfactory. Moreover, the disturbing effects of 

 friction, through varying depths and breadths, and the influence 

 of tributarles ; would perhaps always prevent a cióse approximation 

 between observed facts and theoretical deductions. Still, however, 

 as correct methods of investigation are only second in importance 

 to accurate observations of phenomena ; I trust that the foregoing 

 exposition of what I believe to be the true principies of tidology 

 will not be wholly valueless — which, it will not be, if it only induce 

 those who are better able to deal with the diñiculties of the subject, 

 to examine and refute the errors into which I may have fallen. 



On the physical dlfferenee betiveen a rush of water like a torrent 

 down a channel and the transmission of a JVave down a river — ivith 

 reference to the Inundation of the Indus, as observed at Attock, in 

 August, 1858. — By Archdeacon J. H. Pratt. 



The following paper is the substance of some remarks I made at 

 the monthly meeting of the Asiatic Society early in September, after 

 the reading of Mr. Obbard's paper published above. That interesting 

 communication was shown to me and to one or two other members 

 when it was first forwarded to the Society, and a discussion which 

 ensued persuaded me that some further explanation of the manner in 

 which a wave may have been generated on the Indus, as supposed 

 by Mr. Obbard, by the bursting of a bund and the precipitation of 

 the pent-up waters, would not be unacceptable. 



I do not stand forth precisely as the advócate of the view, that 

 the rise and fall of the water at Attock was produced by the trans- 

 mission of a wave, rather than by the ordinary rush of water in a 

 swollen river ; because there are several facts, which it is necessary 

 to determine before coming to a decisión. We ought to know whe- 

 ther there are any great bends and shallows in the river ; and the 

 phenomena to be explained ought to be more fully before us. My ob- 

 ject is to show the possibility of such an explanation as Mr. Obbard has 

 advanced ; and to give my reasons for on the whole inclining to the 

 view that the disturbance at Attock was produced by the passage of 

 a wave. J. H. P. 



