30 



Prof. G. H. Darwin, 



[Nov. 22, 



the furrow, the root leaves its crest and moves with very great speed 

 to the left. In iv the root is just passing under the convolutions. 

 The whole system is moving with its maximum velocity, but the root 

 outstrips the stem. The two slopes of the crest are nearly symme- 

 trical. In v the root has gained so far on the convolutions as to have 

 again reached a crest. 



Fig. 10. 



In vi the convolutions have caught up the root, and the crests ar& 

 being displaced. 



Finally vii is a repetition of i in the opposite direction, and the 

 half oscillation is completed. 



If in these figures i to vii we take the wave-length of ripple-mark 

 as unity, the amplitude of oscillation of the main body of water is 2*1, 



