WAVES OF THE SEA 295 



sion, on a slightly larger scale, where the water of 

 the little Pfanenbach flows down a precipitous rock- 

 face near Gunten, on the Thunersee. Here, again, 

 the runnels of water were not wide, and the wave- 

 front of the progressive waves was V-shaped. 



Water flowing in a broad, thin sheet upon a 

 sloping platform goes in progressive wavelets, 

 which have a widely extended wave -front, present- 

 ing a series of parallel ridges, which recall the 

 typical form of surface waves more forcibly than 

 the V-shaped wavelets of a film flowing in a narrow 

 runnel. I have detected the progressive -wavelet 

 form of flow on the face of a vertical slab of 

 smooth stone down which water flowed, but have 

 seen it better upon the sloping, polished marble 

 slab of a fishmonger's shop when being washed 

 down with water flowing from a pipe. The out- 

 flow from the pipe may not have been absolutely 

 steady ; but any unsteadiness there may have been 

 was certainly slight, whereas the flow of the sheet 

 of water rapidly formed itself into a procession 

 of progressive wavelets, which were both con- 

 spicuous and regular. The ridges were about 

 9 inches apart . The same thing can be seen where 

 the street pavement or a ship's deck is flushed from 

 a large hose. 



