350 WAVES OF THE SEA 



waves are more conspicuous relatively to the 

 diverging waves than in rougher water, and that 

 their relative prominence is further increased when 

 the wave -track is viewed from a height. At alti- 

 tudes of from 300 to 800 feet on the steep slope 

 above Gunten, opposite to Spiez, the number of 

 visible thwart -ship waves in a single series must 

 have amounted to hundreds, the water looking like 

 corded silk. Unfortunately, the condition of glassy 

 water is often accompanied by a slight haze, which 

 makes it impossible then to obtain a strong photo- 

 graph. 



I saw nothing in the appearance of the train of 

 thwart waves different from that indicated by Lord 

 Kelvin's diagram, and nothing different from what 

 is seen at sea, except their greater distinctness. 

 The case of the diverging waves, however, was 

 very different. Only the outer edge of the group 

 presents the uninterrupted concave fronts of the 

 diagram. Behind this comes a row of notches in 

 the wave -fronts, which row appears from a dis- 

 tance as a strongly marked band, light or dark 

 according to the circumstances of reflection. 

 Standing near the stern of a steamer, I was able to 

 see distinctly that the first notch occurred where 

 a diverging wave of the bow series was crossed 

 by the first diverging wave of the series which 



