﻿Effect of Electricity on Streams of Water Drops. 149 



(1) No perceptible difference in the appearance of the 

 streams as they break into drops is betrayed. 



(2) In each stream there is very apparent non-uniformity 

 in the size of the drops in the stream ; this is perhaps to be 

 expected on account of the disturbing influences due to the 

 velocity of the stream and the random vibrations in the air 

 at the point of breaking into drops. 



(3) One striking difference between the jets — a difference 

 much more accentuated in photographs which follow — is the 

 alignment of the drops of the charged stream as they proceed 

 to the summit, and the scattering of the uncharged drops. 

 This is of course in apparent contradiction to the repulsive 

 action one might expect from the fact that the drops in the 

 charged stream are all charged with electricity of the same sign. 



(4) As a consequence of the phenomenon in (3) the charged 

 drops coalesce at the ton of the stream into large non-uniformly 

 sized drops ; the coalescence takes place at the portion of 

 the stream where the velocities have become small and 

 consequently when, as Rayleigh points out, the water in the 

 stream collects into smaller total volume on account of the 

 continuity of the flow. 



Photographs such as those above reveal, however, only 

 half truths ; they represent the effect in the charged streams 

 under only feeble electrifications. When the stream was 

 influenced by charges at the potentials as high as those given 

 by electrical machines or induction-coils, Rayleigh found 

 that the stream indicated strong repulsion between the 

 drops. 



Rayleigh ascribes the whole action in both streams to 

 collisions. In the uncharged stream the drops rebound 

 after collision, and we have the consequent scattering ; while 

 in the charged stream the electrification in some way leads 

 to coalescence. His words are as follows *: — 



" As the liquid masses approach one another the inter- 

 vening air has to be squeezed out. In the earlier stages 

 of approximation the obstacle thus arising may not be 

 important ; but when the thickness of the layer of air is 

 reduced to the point at which the colours of thin plates are 

 visible, the approximation must be sensibly resisted by the 

 viscosity of the air which still remains to be got rid of. 

 No change in the capillary conditions can arise until the 

 interval is reduced to a small fraction of a wave-length of 

 light. But such a reduction, unless extremely local, is 

 strongly opposed by the remaining air. It is of course true 

 that that this opposition is temporary. The question is 

 * Sc. Papers, iv. p. 415, § 251. 



