AND OTHER WATER WAVES 319 



Observation of Roll-waves in the Conduit of the 

 Guntenbach, Gunten, Thunersee, Switzerland 



The Guntenbach, which drains a smaller valley 

 than the Griinnbach, runs for the last 1,000 feet 

 of its course in a paved conduit, with a practically 

 uniform gradient of i in 22, as measured with a 

 small Abney level. The sides of this conduit are 

 sloping, not vertical, as in the Griinnbach ; the 

 paving -stones are more irregular in form, and 

 the depressions at their joints are deeper, as well 

 as less regular. No roll-waves were ever seen 

 in the upper part of the conduit ; ! they originated 

 suddenly lower down, generally at or below the 

 lowest bridge, which was 370 feet from the outfall. 

 Thus the course of events differed considerably 

 from that in the Griinnbach, where the waves could 

 be watched through all their stages of development. 

 On the roughly-paved Guntenbach it took much 

 watching to discover the origin of the roll-waves. 

 I would stand near by where they generally com- 

 menced, watching the water closely ; then, to the 

 right or to left of where I was looking, I would hear 

 a sudden sound like that of the word " flop," and, 



1 The upper part of the conduit has in many places deep 

 longitudinal grooves in the central paving-stones. The cross- 

 section of the lower part is more nearly uniform. 



