THE SPLASH OF A DROP AND ALLIED PHENOMENA. 209 



sufficient for pliotograi)hy. When the current strength was increased, 

 so as to make the ilkimiuation bright enough for the camera, then the 

 spark became of too great duration, for it lasted for between four and 

 five thousandths of a second, within which time there was very per- 

 ceptible motion of the drop and consequent blurring. It was therefore 

 necessary to modify the apparatus so as to employ a Leyden-jar spark 

 whose duration was probably less than ten-millionths of a second. A 

 very slight change in the apparatus rendered it suitable for the new 

 conditions, but time does not permit me to describe the arrangements 

 in detaih It is, however, less necessary to do so as the method is in 

 all essentials the same as that described in this room two years ago by 

 Lord Eayleigh in connection with the photography of a breaking soap- 

 film.' I therefore pass at once to the photographs themselves. 



The first two series (Plates X, XI) may be described as shadow photo- 

 graphs. They were obtained by allowing a drop of mercury to fall 

 onto the naked photographic plate itself, the illuminating spark being 

 produced vertically above it, and they give only a horizontal section of 

 the drop in various stages. The first series corresponds to a mercury 

 splash very similar to that first described, and the second to the splash 

 of a larger drop such as was not described. In each series the tearing 

 of the thin central film to which allusion was made is well illustrated. 

 I think the first comment that anyone would make is that the photo- 

 graphs, while they bear out the drawings in many details, show greater 

 irregularity than the drawings would have led one to expect. On this 

 point I shall presently have something to say. 



Comparing the first set of drawings with the photographs of Series 

 X, it will be seen that photograph 2 corresponds to drawing 4 or 5; 

 photograph 3 to that of 9; photograph 4 to that of 18; i)hotograph G 

 to that of 20, and photograph 7 to that of 24, but the irregularity of 

 the last photograi)h almost masks the resemblance. 



ISeries XII (Plate XII) gives an objective view of a mercury splash as 

 taken by the camera. Only the first of this series shows any detail in the 

 interior. The polished surface of the mercury is, in fact, very trouble- 

 some to illuminate, and this splash proved the most difficult of all to 

 l^hotograph. 



Series XIII (Plate XIII) shows the splash of a drop of milk falling 

 onto a smoked-glass plate, on which it runs about without adhesion, 

 just as mercury would. Here there is much more of detail. In fig. 4 

 the central film is so thin in the middle that the black plate beneath it 

 is seen through the liquid. In fig. 8 this film has been torn. 



Series XIV (Plates XIV, XV) exhibits the splash of a water drop 

 falling into milk. The first four photographs show the oscillations of 

 the droi) about a mean spherical figure as it apjiroaches the surface. 



'A tletailed account of the optical, mechanical, and electrical arrangements 

 emi)loyed, written by Mr. Cole, will be found in Nature, Vol. 1, page 222 (July 5, 

 1894). 



SM 94 H 



