VIEWS OF RUNNING WATER. 



6 47 



lake. Besides, the two points being possibly distant from one 

 another, the effect, or the eddy, appears before the cause, the ob- 

 stacle (Fig. 1, ii). It is in this way, by the appearance of the surface, 

 that the raftsman going down a river can judge, from the varia- 

 tions of speed, of the depth of the stream, and the size and posi- 

 tion of reefs hidden under the water, frequently a considerable 

 distance below the point where he is. Is not this the supreme 

 end of art to cause to be foretold by outer forms what is going 

 on in the domain of invisible things, and to divine the reality 

 without laying it bare ? Water lends itself eminently to this end. 

 It obeys mechanical laws, not as a machine which exposes them 

 bluntly and fatally, but with a variety of suggestions and a light- 

 ness that leave the field clear for the imagination. 



Let us, in our experimental canal, reduce the dam to a single 

 obstacle in the middle of the stream. The eddy-wave, instead of 

 being straight, bends around on either side, and takes the form of 

 a parabola with a A more or less open according to the velocity 

 of the stream. Moreover, the branches of the parabola, turned 

 back by the side-walls of the canal, if it is not too broad, take a 

 figure below the obstacle in which the first traces of a lozenge 

 appear (Fig. 2, iii). Lastly, let us place the obstacles on the sides 



Fig. 2. Forms of Eddy-waves. 



of the canal. We find that the waves are turned toward the mid- 

 dle of the stream, and that by intercrossing with those coming 

 from the opposite bank, and by their own return, a system of 

 lozenges is produced on the surface of the water (Fig. 2, iv, and 

 Figs. 3 and 4). 



In this we see the pre-eminently typical phenomenon of run- 

 ning water. Every inequality of the shore, whether promontory 

 or bay, plant or pebble, stake or bridge pier, is the starting-point 

 for centripetal lines which go on in graceful undulations to lose 

 themselves in the stream, or, meeting with others, to form qua- 



