]44 
PROFESSOR A, M. WORTHIXGTOX AND MR. R. S. COLE 
studies showing the babble opening quite centrally I’ound the emergent column, and 
the fact that the base of this does not photograph shows how completely the original 
milk drop is collected at the top of the column. Sub-group B illustrates what 
happens when, as in Photograph 18, the top of the bubble is struck by the column 
and burst at one side. Under the influence of the surface tension, rotundity of form 
is soon regained, and by the time the stage of Photograph 21 is reached all traces of 
previous irregularities have disappeared. 
Examination with a lens of Photographs 3, 4, and 5 shows how the drop, on fli’st 
entering, punches a very sheer-walled hole.* From the fact that these early stages 
photograph so Avell as compared (see next series) Avith corresponding stages when the 
drop is of Avater and the liquid is milk, we infer thaP the first liquid thrown up is 
milk drawn from the fringe of the drop itself. It must be remembered that OAving to 
the closeness of the camera, front and back parts of the crater cannot be quite in 
focus together. The first flow of the liquid appears to be very much along the 
surface, afterAvards it is much more perpendicular to the surface, and this alone 
appears sufficient to account for the sharp curling-OA’er of the edge of the crater 
(Photograjahs 4 to 6); for superposition of the photographs seems to show- that in the 
early stages each particle continues to moAm for some distance in the straight line 
along Avhich it Avas first projected from the surface. As to the reason of the closing 
in of the crater shall make some remarks in connection with the next series. 
Series III. (Pla,te 3).—This gives, in 24 photographs, the splash of a Avater-drop 
Aveighing '4 gram, falling from a still greater height, 137 centims., into milk mixed 
with Avater. Taken Avith the quartz spectacle lens. Scale -g linear. The crater 
closes up at a much earlier stage and forms a bubble Avhich becomes smoother in out¬ 
line as the liquid drains doAvn its sides or distributes itself more evenly OAmr its Avails. 
This bubble may remain closed (Photograph 16) or may open at a comparatUely early 
stage, following the course shoAvn by Photographs 13, 11, and 18. Or it may be 
from the first much depressed by the hearty mass of liquid at its top (Photographs li, 
15, and 17). Sub-group A shoAvs the configurations of earlj" stages Avhen the Avater- 
drop is exchanged for an equal drop of milk and falls into Avater. The increase in 
visibility is very marked. The original of No. 1A bears examination Avith a lens. In 
Sub-group B the crater obtained Avas smaller than usual, perhaps through the drop 
striking the Avater in a very prolate form, as in Series I., Photograph ]. 
With respect to the closing-in of the crater, it Avill be noticed that in Photographs 6, 
7, and 8, the upper edge is surmounted by a rim of greater thickness than the walls 
beloAV ; there can be no doubt that the accumulation of liquid here is due to the 
upAvard floAv being checked by the surface tension. When such an annular rim is 
formed, an elementary calculation shoAvs that the centripetal acceleration Avith Avhich 
*■ So much of the detail of the oi’igiiial photographs has been lost in the reproductions tliat it is only 
in fig-. 5 that the edge of the vertical cliff of liquid is visible at tlie far side of the crater. Tins edge 
marks the free horizontal surface of the, as yet, undisturbed liquid, 
