THE SPLASH OF A DROP AND ALLIED PHENOMENA.' 



By Prof. A. M. WoRTiiiNfrTON, M. A., F. R, S. 



The splash of a drop is a transaction which is accomplished in the 

 twinkling' of an eye, and it may seem to some that a man who proposes 

 to disconrse on the matter for an hour must have lost all sense of i)ro- 

 portion. It' tliat oi)inion exists, I hope this evening to be able to 

 remove it and to convince you that we have to deal with an exquisitely 

 regulated phenomenon, and one which very happily illustrates some 

 of the fundamental in'operties of fluids. It may be mentioned also 

 that the recent researches of Lenard, in Germany, and J. J. Thomson, 

 at Cambridge, on the curious development of electrical charges that 

 accompanies certain kinds of sj)lashes have invested with a new 

 interest any examination of the mechanics of the phenomenon. It is 

 to the mechanical and not to the electrical side of the question that I 

 shall call your attention this evening". 



The first well-directed and deliberate observations on the subject 

 that I am acquainted with were made by a schoolboy at Rugby some 

 twenty years ago, and were reported by him to the Rugby Natural 

 History Society. He had observed that the marks of accidental 

 splashes of ink drops that had fallen on some smoked glasses with 

 which he was experimenting, presented an appearance not easy to 

 account for. Drops of the same size falling from the same height had 

 made always the same kind of mark, which when carefully examined 

 with a lens showed that the smoke had been swept away in a system 

 of minute concentric rings and fine stria'. Specimens of such j)at- 

 terns, obtained by letting drops of mercury, alcohol, and water fall onto 

 smoked glass, are thrown on the screen, and the main characteristics 

 are easily recognized. Such a i)attern corresponds to the footprints of 

 the dance that has been performed on the surface, and though the 

 drop may be lying unbroken on the plate, it has evidently been taking 

 violent exercise, and were our vision acute enough we might observe 

 that it was still palpitating after its exertions. 



A careful examination of a large number of such footprints showed 

 that any opinion that could be formed therefrom of the nature of the 



1 Address at weekly evening meeting, May 18, 1894, Royal Institution of Great 

 Britain. Printed in proceedings of the Eoyal Institution. 



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