1894.] on the Splash of a Drop and Allied Phenomena. 293 



thus cuts off the current of the electromagnet C. This lets off drop 

 and sphere, and produces the flash. The stage of the phenomenon 

 that is thus revealed having been sufficiently studied by repetition 

 of the experiment as often as may be necessary, he lowers the plate 

 D a fraction of an inch and thus obtains a later stage. Not only is 

 any desired stage of the phenomenon thus easily brought under ex- 

 amination, but the apparatus also affords the means of measuring the 

 time interval between any two stages. All that is necessary is to 

 know the distance that the timing sphere falls in the two cases. 

 Elementary dynamics then give us the interval required. Thus, if 

 the sphere falls one foot and we then lower D J inch, the interval 

 between the corresponding stages will be about ■ 0026 second. 



Having thus described the apparatus, which I hope shortly to show 

 you in action, I pass to the information that has been obtained by it. 



This is contained in a long series of drawings, of which a selec- 

 tion will be presented on the screen. The First Series that I have 

 to show represents the splash of a drop of mercury 0*15 inch in dia- 

 meter that has fallen 3 inches on to a smooth glass plate. It will be 

 noticed that very soon after the first moment of impact, minute rays 

 are shot out in all directions on the surface. These are afterwards 

 overflowed or united, until, as in Fig. 8, the outline is only slightly 

 rippled. Then (Fig. 9) main rays shoot out, from the ends of which 

 in some cases minute droplets of liquid would split off, to be left 

 lying in a circle on the plate, and visible in all subsequent stages. 

 By counting these droplets when they were thus left, the number of 

 rays was ascertained to have been generally about 24. This exquisite 

 shell-like configuration shown in Fig. 9, marks about the maximum 

 spread of the liquid, which, subsiding in the middle, afterwards flows 

 into an annulus or rim with a very thin central film, so thin, in fact, 

 as often to tear more or less irregularly. This annular rim then 

 divides or segments (Figs. 14, 15, 16) in such a manner as to join 

 up the rays in pairs, and thus passes into the 12-lobed annulus of 

 Fig. 16. Then the whole contracts, but contracts most rapidly be- 

 tween the lobes, the liquid then being driven into and feeding the 

 arms, which follow more slowly. In Fig. 21 the end of this stage is 

 reached, and now the arms continuing to come in, the liquid rises in 

 the centre ; this is, in fact, the beginning of the rebound of the drop 

 from the plate. In the case before us the drops at the ends of the 

 arms now break off (Fig. 25), while the central mass rises in a 

 column which just fails itself to break up into drops, and falls back 

 into the middle of the circle of satellites which, it will be understood, 

 may in some cases again be surrounded by a second circle of the 

 still smaller and more numerous droplets that split off the ends of 

 the rays in Fig. 9. The whole of the 30 stages described are accom- 

 plished in about -^ second, so that the average interval between 

 them is about ^^ second. 



It should be mentioned that it is only in rare cases that the sub- 

 ordinate drops, seen in the last six figures, are found lying in a very 



