11)0 



MESSRS. A. M. WOUTHIXGTON .VXD 1!. S. DOLE 



after the photographs had been developed. In each case the sphere was dusted on 

 the right-hand side along a narrow vertical strip. In No. 5 the tangent from the 

 highest drops on the right again leads accurately to the place of departure of the 

 liquid. In fig. 6 the pocket of air has apparently been swept up the surface of the 

 sphere, perhaps by the converging flow already noted. 



Fig. 5. 



Series XX. 



Fig. <-. 



We observe that in figs. 1 and 2 (same Series XX., Plate 3) the continuous film or 

 shell of liquid no longer reaches the outermost droplets that once have been at its 

 edge. It must evidently have been pulled in by its own surface tension, which of 

 course will cease to exercise any inward pull on a drop that has once separated. 



The influence of dust, thus incontestably proved, seems to afford a satisfactory 

 explanation of 



(1) The effect of a flame. 



(2) The effect of heating. 



(3) The variable and uncertain effects of electrification. 



For (1) we may suppose that the flame burns off minute particles of dust ; (2) we 

 know from AITKEN'S experiments that dust from the atmosphere will not settle on a 

 surface hotter than the air ; (3) an electrified sphere descending through the air 

 would attract dust to its surface unless it happened, as well might happen, that the 

 air round about it, with its contained dust, had become itself similarly charged 

 through the working of the electrical machine. 



At the same time we cannot claim that our explanation of the influence of a flame 

 is more than a conjecture. For we found that it was only when the brightly 



