ON IMPACT WITH A LIQUID SURFACE. 
147 
millimetre scale, just in contact with the liquid surface at one side. Photograph 
No. 9 shows the general rise of level due to the entry of the sphere. The rise at the 
edge of the scale is about 3 millims., but the rise at the spout of the vessel is much 
more marked, though this is at a greater distance from the place of impact, and the 
liquid enveloping the sphere seems to rise very abruptly out of the flat surface on 
this side. We think that all the facts point to rise of level at great distances from 
the impact even when the vessel is much wider. 
When the ivory sphere, which when dry and well polished gave the splash of 
Series IV., was allowed to fall wet into the liquid, all other circumstances remaining 
the same, the splash of Series VII. (Plate 7) was obtained, which from the very 
first is entirely different. The wetting was effected by dipping the sphere into the 
bowl of milky water in which it was to fall and then shaking off as much as possible 
of the adherent liquid, but in all cases the splash quickly becomes unsymmetrical, 
probably through the liquid during the fall drifting to one side of the sphere, indeed, 
in all the figures from 4 onward, but especially in 4 and 5, there is seen a tendency 
to behave as a smooth dry sphere on the left-hand side where convergent foldings 
may (in the original photographs) be seen on the surface. The confusion arising 
from this want of symmetry made it seem unprofitable to examine this splash any 
further. 
This disturbing want of symmetry entirely disappears, however, when we employ a 
rough sphere, as in Series VIII. and IX. (Plate 8). In Series VIII. the impiuging 
sphere was of marble 1‘5 centims. in diameter, and the height of fall was 15 centims. 
The sphere was on each occasion dried and then well rubbed with emery paper. 
When dipped into the liquid it was at once “ wetted ” in the usual sense of the 
term. Yet the liquid on impact seems to do anything but wet it. The first flow is 
evidently very much along the surface away from the place of impact, and the 
subsequent behaviour of the crater, as far as Photograph No. 14, is very similar to 
that of Series I., which w'as due to the impact of a liquid sphere. Indeed, 
figs. 8 to 10 of tins series hardly differ from Nos. 17-20 of Series I. In the column 
that afterwards emerges there is, however, a very wide difference. In each case it 
rises from the bottom of a hollow, but in the present series it is a far finer jet and 
moving with much greater velocity. This jet was, in fact, observed with the naked 
eye, in continuous daylight, to rise even to a greatei’ height than that from which 
the sphere had fallen. 
Comparing the crater of this series with that of Series I., we observe that while 
the outside dimensions are not very different, the crater of the present series is 
distinctly thinner in the wall, also that the number of lobes or arms is larger. The 
number seems always to be decided at a very early stage, and to be due, as was 
suggested (Worthington, ‘ Proc. Pmy. Soc.,' 1882, Joe. cit.), to the instability of the 
annular rim. Thus, in Series I., fourteen appears to be a frequently recurring number 
in the earlier stages, and in Series VIII., twenty-six or twenty-eight, and in both 
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