Impact with a Liquid Surface. 



153 



VIII. "The Thermal Expansion of Pure Nickel and Cobalt." By 

 A. E. Tuttox, B.Sc. Communicated by Professor TlLDEN, 

 F.R.S. 



The Society adjourned over Ascension Day to Thursday, May 18. 



" Impact with a Liquid Surface, studied by the aid of Instanta- 

 neous Photography. Paper II." By A. M. Worthtngton, 

 M.A., F.R.S., and E. S. Cole, M A. Received March 21 — 

 Read May 4, 1899. 



(Abstract.) 



This paper is a continuation of a paper under a similar title, published 

 in the ' Philosophical Transactions,' A, vol. 189, 1897. 



It was there shown that between the splash of a rough and that of a 

 polished sphere falling the same distance into water, there is a remark- 

 able difference from the first moment of contact. The causes of this 

 difference are now investigated. 



The configuration of the water surface below the general level, when 

 a rough sphere enters, is first studied by instantaneous photography, 

 and the origin is traced of the bubble that follows in the wake of the 

 sphere and of the emergent jet which follows its disappearance. The 

 depression or crater formed round the entering sphere is surprisingly 

 deep. This cavity segments, the lower part following as a bubble in 

 the wake of the sphere, while the upper part fills up by the influx of 

 surrounding water, which gathers velocity as it converges towards the 

 axis of the disturbance, and so produces the upward spurt of the jet. 



Experiments are described in which some idea of the actual dis- 

 placements in the liquid has been obtained by letting the sphere 

 descend between two vertical slowly ascending streams of minute 

 bubbles liberated by electrolysis from two pointed electrodes. 



It is found that with a gradual increase in the height of fall of a 

 well-polished sphere, the splash changes in character, and that the 

 sphere soon begins to take down air. But the height at which this is 

 first noticeable is largely dependent on minute differences in the con- 

 dition of the surface, and even on its temperature. It was further 

 found that dropping a smooth sphere through a flame, under certain 

 conditions, invariably alters entirely the course of the splash. This 

 action of the flame is proved to be no action of electrical discharge, 

 and reasons are given for attributing it to the burning off of fine dust 

 which has collected on the surface during the fall. 



The influence of dust was proved by dusting one side only of a 

 polished sphere, a proceeding which always results in completely 

 changing the character of the splash on the dusted side. 



