It will be observed that as the drop descends into the liquid the upper portion is at first not appreciably distorted, but that a little cup or crater of liquid is thrown up round it. As the drop descends further, this crater grows wider and higher and thicker in the wall, and jets are shot out from its edge or rim. These jets are visible even in the second figure. The black marks on the inside wall of the crater are due to the lamp-black carried down with the drop from the smoked surface of the supporting cup: though in one sense a disfigurement, they serve to show by their presence that the interior of the crater _is lined by the original liquid which formed the drop_, and thus afford useful information as to the nature of the flow. The crater rises with great rapidity up to Fig. 4. In Fig. 5 the walls are beginning to grow thicker, while the next three figures show the crater subsiding and widening, till in Fig. 9 it lies as a mere ring of lobes on the surface, surrounding a central hollow. [Illustration: SERIES I Milk into water (40 cm.). Scale 3/4. 1 2 T = 0 3 0·002 sec. 4 0·007 sec. 5 0·018 sec. 6 0·031 sec. 7 0·040 sec. 8 0·050 sec. 9 0·056 sec.] Fig. 10 shows the beginning of the rebound, in the rising of a central column. It will be seen that the lamp-black is now all swept to the middle, indicating that _the liquid of the original drop emerges at the head_ of the central column. Full confirmation of this is obtained from Fig. 12, which represents the emergent column obtained when the circumstances are all the same, except that we have a drop of milk falling into water instead of water falling into milk. It will be observed that the upper part only of the column is visible, precisely because it contains nearly all the milk of the drop, while the lower part, consisting chiefly of transparent water, remains invisible. [Illustration: SERIES I--(_continued_) 10 0·064 sec. 11 0·073 sec. 12 13 0·093 sec.] No. 15 shows the column at its greatest height, and it should be noticed that Figs. 16 and 17 show a tendency on the part of the head of this column to split off as a separate drop. [Illustration: SERIES I--(_continued_) 14 0·103 sec. 15 0·116 sec. 16 0·129 sec.] The column in subsiding forms a "cake" of liquid round the base. The edge of this circular cake (see Figs. 17, 18, and 19) is the first well-marked ripple spreading outwards in an ever-widening circle. [Illustration: SERIES I--(_continued_) 17 0·153 sec. 18 0·197 sec. 19 0·217 sec.]