January 7, 1892' 



NATURE 



231 



dulatory movement of the body, propagating from the 

 head to the tail. 



In observing the movements of many other different 

 species of serpents, both in and out of water, Prof. Marey 

 says : " La reptation des uns et la natation des autres 

 pr^sentent de grandes analogies avec la natation de 

 I'anguille, mais nous n'y avons pas trouvd la meme 

 rdgularitc des mouvements." 



But in the study of the movements of objects as small 



-Eel swimming in a horiz ntal plane. The horizontal line ^o shows 

 j plainly the inclination of those lines which join the crests and troughs of 



! the waves formed by the body, so that the velocity of progression of the 



a;iimal is expressed by the inclination of the line oa. 



as these, Prof. Marey does not here conclude his obser- 



: vations, but has constructed a special piece of apparatus, 



I as shown in Fig. 9, for recording the movements of 



: microscopical objects. The general working of this 



apparatus can be seen at a glance, c is the large 



condenser which concentrates all the light from some 



artificial source on to the small holder/, in which the 



object is placed. The micrometer objective marked O, 



performed by a < 



turning itself over. 



Fig. 8, illustrating an eel swimming horizontally, brings 

 out clearly the wave produced by the effect of the un- 



NO. I 158, VOL. 45] 



Fig. 9. — Special piece of apparatus for studying the movements of micro- 

 scopical objects. 



is placed on the other side of this holder, but in the axis 

 of the condenser. The micrometer head B regulates the 

 distance of p from o, and can be moved either by the 

 rod viv, or by its milled head. An important adjunct to 

 the instrument is the microscope that is placed obliquely 

 at the side of the camera ; by its means, and by that of a 

 small prism that can be placed in the axis of the light by 

 simply pulling or pushing the knob P, the object about 



