By very careful rubbing of such a polished, steel sphere, it was found possible to increase the height of fall to 162·5 cm. (well over 5 feet) and yet to secure a perfectly "airless," "smooth" splash. But the equilibrium of the splash, if I may use the phrase, is, at this high velocity of entry (564 cm. per sec., or about 18 feet per sec.), very unstable, and was found to depend on minute differences in the condition of the surface. How minute this difference may be, which yet makes the whole difference in the character of the splash, may be gathered from the following extract from the original paper:-- "A polished steel sphere 15·9 cm. in diameter was found (by naked-eye observation) to give an airless splash when falling into water from a height of 132·5 cm.; at 137·5 cm., there was much air taken down. This observation at 137·5 cm. was repeated three times, observer C. doing the polishing. Then observer W. polished, and the splash was first _nearly_ airless and then _quite_ airless. Then, by persevering in the rubbing, the height of fall was gradually raised to 162·5 cm., and a perfectly airless splash was secured, and even at 172·5 cm. the record was 'very little air indeed.' "Again, a polished marble sphere 2·57 cm. in diameter falling into water from a height of 112 cm. was found to take down 'much air' when rubbed with a certain clean handkerchief A, and 'none at all, or only very little,' when rubbed with clean handkerchief B. This result was confirmed four times with B and five with A. These handkerchiefs were subsequently examined under the microscope, but were found to be extremely similar, and the cause of the difference remained for the time beyond conjecture. "On another occasion, of two similar nickel-plated steel spheres, each 19 millimetres in diameter, and each treated in exactly the same way, falling 22 cm. into paraffin oil, one would always take down much air and the other little or none, and again microscopic examination showed only a very slight difference in the surfaces." [Illustration: SERIES XII Smooth sphere of polished serpentine falling 100 centim. into water. Scale 3/4. 1 T = 0 2 0·001 sec. 3 0·002 sec.] By wetting the surface of a smooth sphere we can always convert a smooth or "sheath" splash into a rough or "basket" splash. Thus when the ivory sphere (which when dry and well-polished gave, with a fall of 60 cm., the splash of Series XI, p. 97), was allowed to fall _wet_ into the liquid, all other circumstances remaining the same, the splash of Series XIII, p. 103, was obtained, which is entirely different from the first. The wetting was effected by dipping the sphere into the bowl of milky water into which it was to fall, and then shaking off as much as possible of the adherent liquid, but in all cases the splash quickly became unsymmetrical, probably through the liquid, during the fall, drifting to one side of the sphere. INFLUENCE OF THE NATURE OF THE LIQUID.