APPLICATIONS TO MECHANICS 



97 



above and below. Behind the obstacle they form a 

 number of eddies. We have also investigated the 

 effect of a current of water coming in contact with 

 a body of pisciform shape, that is to say, a solid body, 

 the section of which tapers off unequally at the two 

 extremities.* 



Fig. 66. — A current meeting a pisciform body at its thick end. 



Experiments of this kind demonstrate in the case of 

 fish the mechanism of swimming. They might also be 

 useful for ascertaining experimentally the shapes which 

 offer least resistance, either in the case of bodies im- 

 mersed in flowing: water or of those moving in still 



-A current- meeting a piscifu 



water. The conditions, according to most authorities, 

 are reversible. 



The extent to which eddies occur, or, in other words, 

 the loss of energy, may be regarded as a measure of 

 the resistance offered to bodies immersed in a current. 



* In order that the light might pass up through such a body, the 

 sides were made of ebony, and the superior find inferior surfaces of 

 celluloid — the contour of a fish being preserved throughout. The 

 light which pas.-ed through the layers of celluloid was sufficient to 

 illuminate the bright beads which happened to pass above the 

 obstacle, and consequently their images appeared in the chrono- 

 phot graphic negatives, and showed the paths taken by the various 

 eddies. 



