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THE POPULAR SCIENCE MONTHLY. 



drilles of rhombs, often with the most charming effect. By the 

 direction of these lines the observer divines the course of the cur- 

 rent, and their inclination furnishes him with an exact measure 

 of its velocity. 



In the case of cascades, the greater variety of the phenomena 

 forces us to go more into detail. We begin with an inclined ves- 

 sel, glass, pot, or pail, in process of emptying. How does the sur- 



Eig. 3. System of Lozenges produced by Eddy-waves. 



Fig. 4. System of Lozenges produced by Eddy-waves. 



face of the outrunning liquid look ? It would be safe to wager 

 ten to one that any person at the first instance would represent it 

 as in Fig. 5, v, by parallel parabolic lines. We not rarely find 

 artistic productions in this style dating from the time when they 

 composed landscapes from fancy in their studios. Without being 

 too severe on these errors, which are still not far away from us, 

 we will try to do better, and to correct the faults of the figure, 

 one at a time. 



We lay aside, for the moment, the usual ribbon-like form, 

 which is false, and examine first the question of the vertical lines. 

 They are formed by the series, A, a, a, of points by which the 

 same molecule of water passes (or is supposed to pass) successively. 

 Is there any proof of their material existence ? No. It must be 

 admitted that in certain cases, like that of a thin sheet falling from 



