THE SPLASH OP A DROP AND ALLIED PHENOMENA. 203 



regular row of drops, but they would be farther 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 topide into drops just as if it were 

 straight. This I can show you by a direct experiment. I have here a 

 small thick disk 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 disk face downward on the horizontal 

 lace of the lantern condenser, and through one of two small holes 

 bored through to the back of the disk I iill the groove with quick- 

 silver. Now, suddenly lifting the disk from the plate I release an annu- 

 lus of liquid, which splits into the circle of very equal droj^s which you 

 see projected on the screen. You will notice that the main drops have 

 between them still suuiller 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 hai)pens in all the splashes 

 that we shall examine. Thus in iig. V2 we have an annular rim, which 

 in figs. 13 and 14 is seen to topple into lobes by which the rays are 

 united in i)airs, and even the si)ecial rays that are seen in Iig. 9 owe 

 their origin to the segmentation of the rim of the thin disk 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. Anyone may notice how, as it curls over, the 

 wave presents a long smooth edge, from which at a given instant a 

 a multitude of jets suddeidy 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 topi^les into alternate convexities 

 and concavities; at the former the liow is helped, at the latter hin- 

 dered, 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 endeavor 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 onto the horizontal condenser plate of the lantern, through 

 wliich the light passes upward, to be afterwards thrown ui)on this 

 screen. The illuminating flash will be made inside the lantern, where 

 the arc light would ordinarily be placed. I have now set a drop of 

 mercury in readiness and put the timing si)here in place, and now if 

 you will look intently at the middle of the screen I will darken the 

 room and let off the splash. [The experiment was repeated four or 



' See WortliiugtDU on tlie "Spontaneous segmentation of a liquid annulus," Proc, 

 Roy. Soc, No. 200, page 49 (1879). 



