94 MOVEMENT 



best marked, and sometimes indeed the only portion 

 visible.* 



Intrinsic Movements of Fluid Waves. — A number of 

 the bright beads previously spoken of should be 

 thrown into the tank and the water disturbed, so as 

 to create either waves or a chopping condition. The 

 trajectory of these beads in different parts of the 



Fig. 62.— Molecular movements within a simple chopping wave. 



waves can then be seen in the photographs, and 

 consequently the intrinsic or molecular movements 

 which occur in the same situations. In Fig. 62 is 

 represented the appearance of a simple chopping wave 

 as viewed from the side. Within this wave the mole- 

 cules are seen oscillating, vertically in the ventral seg- 

 ments, horizontally at the nodes, and obliquely in the 



Fig. 63.— Molecular movements within a series of chopping waves of short period. 



intermediate positions. To follow the phases of this 

 movement with greater facility the waves should possess 

 a very short period, for there the molecules may be 

 seen describing curves, the centres of which are at the 

 nodal points. These facts confirm the analytical 

 studies of my colleague Boussinesq. 



* It seems that, owing to the advance of the wave, the meniscus 

 disappears from the advancing surface of the wave, that is to say, 

 from the anterior side. 



