236 



THE FORMS OF CELLS 



[CH. 



splashes, it was found that the fall of a round pebble into water 

 from a considerable height, caused the rise of a filmy sheet of water 

 in the form of a cup or cylinder ; and the edge of this cylindrical 

 film tended to be cut up into alternate lobes and notches, and the 

 prominent lobes or "jets" tended, in more extreme cases, to break 

 off or to break up into spherical beads (Fig. 70)*. A precisely 

 similar appearance is seen, on a great scale, in the thin edge of a 

 breaking wave : when the smooth cylindrical edge, at a given 

 moment, shoots out an array of tiny jets which break up into 

 the droplets which constitute " spray " (Fig. 71, a, b). We 

 are at once reminded of the beautifully symmetrical notching on 

 the calycles of many hydroids, which little cups before they became 

 stiff and rigid had begun their existence as liquid or semi-liquid 

 films. 



Fig. 71. A breaking wave. (From Worthington. ) 



The phenomenon is two-fold. In the first place, the edge of 

 our tubular or crater-like film forms a liquid ring or annulus, 

 which is closely comparable with the liquid thread or cylinder 

 which we have just been considering, if only we conceive the thread 

 to be bent round into the ring. And accordingly, just as the thread 

 spontaneously segments, first into an unduloid, and then into 

 separate spherical drops, so likewise will the edge of our annulus 

 tend to do. This phase of notching, or beading, of the edge of 

 the film is beautifully seen in many of Worthington's experiments'}". 

 In the second place, the very fact of the rising of the crater means 

 that liquid is flowing up from below towards the rim ; and the 

 segmentation of the rim means that channels of easier flow are 



* A Study of Splashes, 1908, p. 38, etc. ; Segmentation of a Liquid Annulus, 

 Proc. Roy. Soc. xxx, pp. 49-60, 1880. 



f Cf. ibid. pp. 17, 77. The same phenomenon is beautifully and continuously 

 •evident when a strong jet of water from a tap impinges on a curved surface and then 

 shoots off it. 



