AND OTHER WATER WAVES 353 



originates at the stern. The steamer which showed 

 this best was the Spiez, a small screw vessel, the 

 others being paddle steamers. Behind this row 

 of notches (i.e., nearer to the line of the ship's 

 course) were many other rows. I have counted 

 in a good light as many as eighteen of these 

 " interference bands " as I term them. When the 

 water is quite glassy they are sometimes more con- 

 spicuous than the individual waves. The photo- 

 graph reproduced in the Plate on page 361 



w 



was taken on Coniston Water. It shows, not only 

 the notches in the wave fronts, but, on the right, 

 the vertical inflection on the crests of the diverging 

 waves caused by interference. This causes the 

 crest of the diverging waves to appear as a pair 

 of dark stripes separated by a broader bright 

 stripe. The circumstance under which the photo- 

 graph was obtained was peculiar. There was a 

 fine drizzling rain when I started for a tour down 

 the lake by the steam gondola, so I left my camera 

 behind out of concern for its welfare. I found 

 that the whole surface of the lake was covered 

 with a thin scum, which appeared to consist of 

 a very slight film of oily soot, possibly from the 

 smoke of the furnaces and factories which are some 

 miles distant at Ulverston and Barrow. The surface 

 being in this condition, the vessel left a wonderful 



