V] 



THE SHAPE OF A SPLASH 



•237 



created, along which the Hquid is led, or is driven, into the pro- 

 tuberances: and these are thus exaggerated into the jets or arms 

 which are sometimes so conspicuous at the edge of the crater. 

 In short, any film or film-like cup, fluid or semi-fluid in its consis- 

 tency, will, like the straight liquid cylinder, be unstable : and its 

 instability will manifest itself (among other ways) in a tendency 

 to segmentation or notching of the edge ; and just such a peripheral 

 notching is a conspicuous feature of many minute organic cup-like 

 structures. In the case of the hydroid calycle (Fig. 72), we are led 

 to the conclusion that the two common and conspicuous features 

 of notching or indentation of the cup, and of constriction or 

 annulation of the long cylindrical stem, are phenomena of the 

 same order and are due to surface-tension in both cases alike. 



Fig. 72. Calycles of Campanularian zoophytes. (A) C. Integra; 

 (B) C. groenlandica ; (C) C. bispinosa; (D) C. raridentafa. 



Another phenomenon displayed in the same experiments is the 

 formation of a rope-like or cord-like thickening of the edge of the 

 annulus. This is due to the more or less sudden checking at the 

 rim of the flow of liquid rising from below : and a similar peri|)heral 

 thickening is frequently seen, not only in some of our hydroid 

 cups, but in many Vorticellas (cf. Fig. 75), and other organic 

 cup-like conformations. A perusal of Mr Worthington's book 

 will soon suggest that these are not the only manifestations of 

 surface-tension in connection with splashes which present curious 

 resemblances and analogies to phenomena of organic form. 



The phenomena of an ordinary liquid splash are so swiftly 



