THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



APRIL 1894. 



XXXI. On the Electricity of Drops. By J. J. Thomson, 

 M.A., D.Sc, F.R.S., Cavendish Professor of Experimental 

 Physics , Cambridge*. 



DROPS offer many advantages for the investigation of 

 electrical effects, especially of those which involve the 

 contact of dissimilar substances. Perhaps the greatest of these 

 advantages is that when the drops are formed they present a 

 perfectly clean surface to the gas by which they are sur- 

 rounded ; so that the conditions are much more definite than 

 they can be where the surfaces have been long exposed, and 

 have had time to get contaminated by dirt or coated with films 

 of gas of unknown composition. 



The experiments described in this paper relate to the elec- 

 trical effects which occur when a drop of liquid falls on to a 

 plate already coated with a film of the same liquid. It has 

 been known for a long time that peculiar electric effects 

 occur at the feet of waterfalls : at such places the normal 

 distribution of the atmospheric electric potential is disturbed 

 in such a way as to indicate a distribution of negative elec- 

 tricity in the region at the foot of the fall. These effects cannot 

 be due to the waterfall acting like the falling drops in Lord 

 Kelvin's water-dropping electrophorus ; for they are found 

 to occur when the waterfalls are inside caves whose sides are 



* Communicated by the Author. 

 Phil. May. S. 5. Vol. 37. No. 227. April 1891. 2 A 



