296 Professor A. M. Worthington [May 18, 



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 sphere 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 five times, and the figures seen were like those of Series X.) 

 Of course all that can be shown in this way is the outline, or rather 

 a horizontal section of the splash; but you are able to recognise 

 some of the configurations already described, and will be the more 

 willing to believe that a momentary view is after all sufficient to give 

 much information if one is on the alert and has acquired skill by 

 practice. 



The general features of the splash that we have examined are not 

 merely characteristic of the liquid mercury, but belong to all splashes 

 of a liquid falling on to a surface which it does not wet, provided the 

 height of fall or size of the drop are not so great as to cause complete 

 disruption,* in which case there is no recovery and rebound. Thus 

 a drop of milk falling on to smoked glass will, if the height of fall 

 and size of drop are properly adjusted, give forms very similar to 

 those presented by a drop of mercury. The whole course of the 

 phenomenon depends, in fact, mainly on four quantities only : (1) the 

 size of the drop; (2) the height of fall ; (3) the value of the surface 

 tension ; (4) the viscosity of the liquid. 



The next series of drawings illustrates the splash of a drop of 

 water falling into water. 



In order the better to distinguish the liquid of the original drop 

 from that into which it falls, the latter was coloured with ink or 

 with an aniline dye, and the drop itself was of water rendered turbid 

 with finely-divided matter in suspension. Finally drops of milk 

 were found to be very suitable for the purpose, the substitution of 

 milk for water not producing any observable change in the phe- 

 nomenon. 



In Series II. the drop fell 3 inches, and was I inch in diameter. 



[In most of the figures of this and of succeeding series the central 

 white patch represents the original drop, and the white parts round 

 it represent those raised portions of the liquid which catch the light. 

 The numbers at the side of each figure give the time interval in 

 seconds from the occurrence of the first figure, or of the figure 

 marked T = 0.] 



It will be observed that the drop flattens itself out somewhat, and 

 descends at the bottom of a hollow with a raised beaded edge 

 (Fig. 2). This edge would be smooth and circular but for the 

 instability which causes it to topple into drops. As the drop descends 

 the hollow becomes wider and deeper, and finally closes over the 



* Readers who wish a more detailed account of a greater variety of splashes 

 are referred to papers by the author. Proc. Roy. Soc, vol. xxv. pp. 261 and 498 

 (1877); and vol. xxxiv. p. 217 (1882). 



