342 On the Electricity of Drops. 



dripping with moisture, in which cases the water would be 

 falling inside an equipotential surface. 



The subject of the electrification produced by falling drops 

 has been investigated by Lenard, who gives the results of his 

 researches in a most interesting paper, entitled " Ueber die 

 Electricitat der Wasserfalle " (Wiedemann's Annalen, xlvi. 

 p. 584). In this paper Lenard shows that when drops of 

 distilled water fall on to a plate wetted by the water, the drops 

 after striking the plate are positively electrified, while in the 

 air around the place where the drops fall there is a distribu- 

 tion of negative electricity : that no electrical separation 

 takes place until the drops strike against the plate : and that 

 the electrical effect with drops of tap-water is very much less 

 than with drops of distilled water. 



Lenard attributes these effects to the formation of a double 

 coating of electricity over the surface of the drop, the drop 

 itself being coated with positive electricity, while in the air 

 close to the surface of the drop there is a coating of negative 

 electricity. When the drop strikes against the plate some of 

 this external coating gets knocked off, leaving the drop with 

 a preponderating positive charge, the corresponding negative 

 charge going off into the air near to where the drop strikes 

 against the plate. 



Some phenomena I observed when an electric discharge 

 was passing through an exhausted tube led me to the con- 

 clusion that bodies were covered with this double coating of 

 electricity, but that its moment and even its sign depended 

 very much on the nature of the gas surrounding the body on 

 which the coating was situated. I was therefore led to make 

 a series of experiments on the phenomena which accompany 

 the splashing of drops, especially on the effect produced by 

 altering the gas through which the drops fall and the liquid 

 of which the drops are made. 



The methods I used are very similar to those employed by 

 Lenard; they are represented in figs. 1 and 2. The arrange- 

 ment shown in fig. 1 was used to test the effect when different 

 liquids fell through air; that in Hg. 2 when the drops fell 

 through gases other than air. A is an insulated funnel from 

 which the drops fall : the substance of which this funnel was 

 made was not found to produce any effect upon the results. 

 I tried funnels of glass, lead, brass, iron, and silver : the 

 mouth of this funnel dips below the top of a metal tube 

 connected to earth. In fig. 2 the top of this tube is closed by 

 a paraffin stopper through which the funnel passes. The 

 drops fall on the plate B, and after striking against it fall 

 into the vessel C, which is insulated and connected to the 

 liquid in the funnel and to one pair of quadrants of the 



