1846.] ANALOGY FROM THE RIVER RHONE. 185 



mark 2 had advanced by only a small fraction of an inch 

 (0*2) ; but on the other hand the vertical pin at C 1 had ap- 

 proached the station C ~by two inches ; shewing that the motion 

 is here entirely directed outwards and upwards against the bank 

 at C, exactly as an hydrostatic pressure acting on a plastic mass 

 would occasion. The result was the more interesting because 

 it was altogether unexpected. It had not occurred to me that 

 the embaying of the ice could be so complete as to leave no 

 appreciable effect due to the drag of the central ice in the direc- 

 tion of the declivity. 



The precise analogy of the phenomena now described to 

 what obtain when the motion of a stream of water is interrupted 

 by lateral obstacles, will suggest itself to almost every one j but 

 to take an illustration which is not imaginary, I have given, in 

 the annexed figure, a sketch of what occurs in the course of 



Fig. 22. 



the river Rhone at the bridge near Sierre. The course of the 

 current is indicated by the arrows, the pier of the bridge b 

 embays the water at c, where it is whirled about by the tan- 

 gential action of the current, but does not escape ; the wavy lines, 

 e d, indicate the ripple produced by the friction of the central 

 past the lateral portions of the stream, the disturbance from 

 which is propagated towards the shore in the waves/ All 

 that is here described may be still better seen in a sluggish 

 stream, and if it be covered with any kind of scum, it will be 

 torn up into longitudinal shreds between e and d, exactly cor- 

 responding to the position of the icy bands. The nature of 

 the force producing these lines of scum is also well shewn by 



