98 MOVEMENT 



Now, it can be seen that if a fish-shaped body 

 presents its thick end to the moving water the 

 currents track along the sides, thus minimizing the 

 deviation of the stream (Fig. (36) ; but if the direction 

 of the current is reversed, so that the water comes in 

 contact with the pointed end, the water having passed 

 the midship-frame, falls into strong eddies (Fig. 67). 

 This experiment confirms the opinion already held, that 

 a " piscifbrm " shape is the most favourable one that 

 a fish could possess, since the water offers very little 



Fig. 68.— Fluid wave surmounting an obstacle. 



resistance to sncn forms as have the pointed end at 

 the posterior extremity.* 



When a stream rushes violently against an opposing 

 obstacle situated near the surface, the water rises up 

 in a heap, and falls down on the other side in a cascade. 

 This transient phenomenon, the details of which are 

 not visible to the eye, can be registered in all its 

 phases by chronophotography, and in a photograph 

 the successive phases of the heaping up of the water, 

 as it Monies in contact with the obstacle, are shown by 

 the variations in the water-level, while the bright beads 

 serve as an index of the molecular movements- in the 

 depth of the basin. This brief enumeration of the 

 applications of chronoJDhotography for the analysis of 



* Chronophotography might, it appears to us, be applied to the 

 study of movements in air when one wanted to find the rerjistance 

 offered by a body <>f particular shape to a current of greater or le^s 

 velocity. For this purpose a number of light and luminous objects 

 would have to be set floating in the air. 



