302 Professor A. M. Worthington [May 18, 



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 XIII. exhibits the splash of a water drop falling into milk. 

 The first four photographs show the oscillations of the drop about 

 a mean spherical figure as it approaches the surface. 



In the subsequent figures it will be noticed that the arms which 

 are thrown up at first, afterwards segment into drops which fly off 

 and subside (see Fig. 8), to be followed by a second series which 

 again subside (Fig. 11), to be again succeeded by a third set. In 

 fact, so long as there is any downward momentum the drop and the 

 air behind it are penetrating the liquid, and so long must there be 

 an upward flow of displaced liquid. Much of this flow is seen to be 

 directed into the arms along the channels determined by the segmen- 

 tation of the annular rim. This reproduction of the lobes and arms 

 time after time on a varying scale goes far to explain the puzzling 

 variations in their number which I mentioned in connection with 

 the drawings. I had not, indeed, suspected this, which is one of the 

 few new points that the photographs have so far revealed. 



With respect to these photographs,* the credit of which I hope 

 you will attribute firstly to the inventors of the sensitive plates, and 

 secondly to the skill and experience of Mr. Cole, I desire to add that 

 they are, as far as we know, the first really detailed objective views 

 that have been obtained with anything approaching so short an 

 exposure. 



Even Mr. Boys' wonderful photographs of flying bullets were 

 after all but shadow-photographs, and did not so strikingly illustrate 

 the extreme sensitiveness of the plates, and I want you to distinguish 

 between such and what (to borrow Mr. F. J. Smith's phrase) I call 

 an " objective view." 



It remains only to speak of the greater irregularity in the arms 

 and rays as shown by the photographs. The point is a curious and 

 interesting one. In the first place I have to confess that in looking 

 over my original drawings I find records of many irregular or un- 

 symmetrical figures, yet in compiling the history it has been inevit- 

 able that these should be rejected, if only because identical irregu- 

 larities never recur. Thus the mind of the observer is filled with 

 an ideal splash — an " Auto-Splash " — whose perfection may never 

 be actually realised. 



But in the second place, when the splash is nearly regular it is 

 very difficult to detect irregularity. This is easily proved by pro- 

 jecting on the screen with instantaneous illumination such a photo- 



* Three of these photographs, viz. Nos. 11, 12 and 17, are reproduced full 

 size, as a frontispiece, by a photographic process, to enable the reader to form a 

 more correct idea than can be gathered from the engravings, of the amount 

 of detail actually obtained. 



The black streaks seen in Figs. 11, 15, 16 and 17 are due to particles of lamp- 

 black carried down by the drop from the smoked surface on which it rested. 



