148 
ON IMPACT WITH A LIQUID SURFACE. 
series the number afterwards diminishes, often by coalescence, as the annulus subsides 
and thickens. This view of their origin appears to gain confirmation fi.’om the fact 
that there is a larger number in the crater with the thinner walls. It is not, however, 
easy, even from the photographs, to estimate the number very accurately. The 
reader will best ascertain the nature of the difficulty by trying. Sometimes, on 
account of the foreshortening of the front rays, these are more easily counted in 
the image of the crater, that is, reflected by the smooth liquid surface in front of it. 
In Series IX., we have the splash of a rough stone sphere, 1’25 centims. in diameter, 
falling 60 centims., into milky water. Photograph No. 1 shows even better than 
No. 1 of the previous series the way in which the liquid, from the very first, is 
driven away from the sphere. The subsequent crater is very like that of Series II. 
or III. obtained from a liquid sphere, and the manner in which the bubble is formed 
does not seem to differ materially from the course followed in Series III. It is 
jDerhaps doubtful whether the creasing on the left of the neck of the bubble in 
Photograph No. 5 is due to an excess of external air pressure, as suggested on p. 145, 
or whether it is a puckering due to radial inflow, as when the sheath closes over a 
smooth sphere. 
This series terminates the record of phenomena that we have at present to lay 
before the Society. We hoi^e next year to be able to complete the survey, and to 
obtain information as to what is proceeding below the surface, and to secure also a 
succession of photographs of different stages of the same identical splash. 
It will have been noticed that useful information is yielded by the comparison of 
one kind of splash with another, and for this reason it appears desirable that the 
study of each shall be fairly complete and minute. Observations that we have already 
made on the impact of a drop with a solid surface, seem to throw light on some of 
the phenomena that are here described. 
In presenting the results so far obtained without waiting for a further accumulation, 
we are influenced by the reflection that there can be, happily, no doubt about the 
accuracy of the photographic record, and by the hope of eliciting from competent 
judges some expression of opinion as to the value of the investigation, with 
suggestions as to the points which it would be most profitable to elucidate. So little 
seems to be known about the actual behaviour of real, as opposed to imaginary fluids 
that we cannot but think that trustworthy information about the motions that follow 
very simple initial conditions may jirove of real value, and not of merely curious 
interest. 
