AND OTHER WATER WAVES 367 



on opposite courses at such a distance that the 

 outer boundaries of their wave -tracks meet at a 

 small angle. On the glassy waters of the 

 Thunersee, and on a bright day, the new disturb- 

 ances of reflection run along the line of meeting in 

 short bars of light which flash across the water at 

 almost lightning speed, by which I mean a speed 

 much greater than that of any railway train or of 

 any bird in flight. 



