1894.] on the Splash of a Drop and Allied Phenomena. 295 



centres of contiguous drops would be equal to the circumference of the 

 cylinder. This can be shown by calculation to be a consequence of 

 the surface tension, and the calculation has been closely verified, by 

 experiment. If the liquid cylinder were liberated on a plate, it 

 would still topple into a regular row of drops, but they would be 

 further apart ; this was shown by Plateau. Now imagine the cylinder 

 bent into an annulus. It will still follow the same law,* i. e. it will 

 topple into drops just as if it were straight. This I can show you 

 by a direct experiment. I have here a small thick disc of iron, with 

 an accurately planed face and a handle at the back. In the face is 

 cut a circular groove, whose cross section is a semicircle. I now lay 

 this disc face downwards on the horizontal face of the lantern con- 

 denser, and through one of two small holes bored through to the 

 back of the disc I fill the groove with quicksilver. Now, suddenly 

 lifting the disc from the plate I release an annulus of liquid, which 

 splits into the circle of very equal drops which you see projected on 

 the screen. You will notice that the main drops have between them 

 still smaller ones, which have come from the splitting up of the thin 

 cylindrical necks of liquid which connected the larger drops at the 

 last moment. 



Now this tendency to segment or topple into drops, whether of a 

 straight cylinder or of an annulus, is the key to the formation of the 

 arms and satellites, and indeed to much that happens in all the 

 splashes that we shall examine. Thus in Fig. 12 we have an annular 

 rim, which in Figs. 13 and 14 is seen to topple into lobes by which 

 the rays are united in pairs, and even the special rays that are seen 

 in Fig. 9 owe their origin to the segmentation of the rim of the thin 

 disc into which the liquid has spread. The proceeding is probably 

 exactly analogous to what takes place in a sea wave that curls over 

 in calm weather on a slightly sloping shore. Any one may notice 

 how, as it curls over, the wave presents a long smooth edge, from 

 which at a given instant a multitude of jets suddenly shoot out, and 

 at once the back of the wave, hitherto smooth, is seen to be furrowed 

 or " combed." There can be no doubt that the cylindrical edge 

 topples into alternate convexities and concavities ; at the former the 

 flow is helped, at the latter hindered, and thus the jets begin, and 

 special lines of flow are determined. In precisely the same way the 

 previously smooth circular edge of Fig. 8 topples, and determines 

 the rays and lines of flow of Fig. 9. 



Before going on to other splashes I will now endeavour to reproduce 

 a mercury splash of the kind I have described, in a manner that shall 

 be visible to all. For this purpose I have reduplicated the apparatus 

 which you have seen, and have it here so arranged that I can let the 

 drop fall on to the horizontal condenser plate of the lantern, through 

 which the light passes upwards, to be afterwards thrown upon this 



* See Worthington on the " Spontaneous Segmentation of a Liquid Annulus," 

 Pioc. Roy. Soc. No. 200, p. 49 (1879). 



