1894. J on the Splash of a Drop and Allied Phenomena. 301 



sufficient for photography. When the current strength was increased, 

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

 the spark became of too great duration, for it lasted for between 

 4 and 5 thousandths of a second, within which time there was very 

 perceptible motion of the drop and consequent blurring. It was 

 therefore necessary to modify the apparatus so as to employ a 

 Ley den-jar spark whose duration was probably less than 10-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 detail. 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 (X. and XI.) may be described as shadow pho- 

 tographs ; they were obtained by allowing a drop of mercury to fall 

 on to 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 any one would make 

 is that the photographs, 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, 



J? " )> >? " 



4 „ „ 18 



6 „ „ 20 



7 „ „ 24 



but the irregularity of the last photograph almost masks the resem- 

 blance. 



Series 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 photograph. 



Series XIII. shows the splash of a drop of milk falling on to a 

 smoked glass plate, on which it runs about without adhesion just as 



* A detailed account of the optical, mechanical, and electrical arrangements 

 employed, written by Mr. Cole, will be fouud in • Nature,' vol. 1. p. 222 (July 5, 

 1894). 



