302 WAVES OF THE SEA 



shown on the Plate . The lip of the conduit is several 

 feet above the highest level of the lake, and the 

 water leaps the outflow as a waterfall. The object 

 of a structure so considerable as this conduit is, 

 not the accommodation of the usual flow of water, 

 but the provision for the great rush which takes 

 place when a thunderstorm bursts over the Justis- 

 thal, especially in springtime before the snows are 

 melted. Under ordinary conditions, even in wet 

 weather, the average depth of water in the conduit 

 is seldom more than 3 inches. The speed is so 

 great, however, on a slope nowhere less than 

 i in 14, that the discharge is not insignificant. 

 With a depth of about 2 inches, the speed is about 

 i o feet per second ; but if the depth were increased 

 to 3 feet or 4 feet, the speed would, no doubt, 

 be very much greater. 



The last of the series of waterfalls above the 

 conduit discharges the stream into a pool, whence 

 it flows over a piece of slightly hollowed pavement 

 for 5 i feet, when it enters the rectangular channel . 

 The discharge of the upper waterfall is steady, in 

 the sense that there is no cadence, the minor 

 flickerings of one part neutralising those of 

 another. The pool is of irregular depth, and the 

 discharge from it has no regular pulsation. Never- 

 theless, as the water rushes over the slightly 



