1879.] Electricity on Colliding Water Drops. 



407 



Under moderate electrical influence there is no material change in 

 the resolution into drops, nor in the subsequent motion of the drops 

 up to the moment of collision. The difference begins here. Instead 

 of rebounding after collision, as the unelectrified drops of clean water 

 generally or always do, the electrified drops coalesce, and thus the jet 

 is no longer scattered about. When the electrical influence is more 

 powerful, the repulsion between the drops is sufficient to prevent 

 actual contact, and then of course there is no opportunity for amal- 

 gamation. 



These experiments may be repeated with extreme ease and with 

 hardly any apparatus. The diameter of the jet may be about ~ inch, 

 and may be obtained either from a hole in a thin plate or from a 

 drawn-out glass tube. I have generally employed a piece of glass 

 tube fitted at the end with a perforated tin plate, and connected with 

 a tap by india-rubber tubing. The pressure may be such as to cause 

 the jet to rise 18 or 24 inches, or even more. A single passage of a 

 rod of gutta-percha, or of sealing-wax, along the sleeve of the coat is 

 sufficient to produce the effect. The seat of sensitiveness may be in- 

 vestigated by exciting the extreme tip only of a glass rod, which is 

 then held in succession to the root of the jet and to the place of reso- 

 lution into drops. An effect is observed in the latter but not in the 

 former position. Care must be taken to use an electrification so feeble 

 as to require close proximity for its operation, otherwise the dis- 

 crimination of the positions will not be distinct. 



The behaviour of the colliding drops becomes apparent under in- 

 stantaneous illumination. I have employed sparks from an induc- 

 torium, whose secondary terminals were connected with the coatings 

 of a Leyden jar. The jet should be situated between the sparks and 

 the eye, and the observation is facilitated by a piece of ground glass 

 held a little beyond the jet, so as to diffuse the light ; or the shadow 

 of the jet may be received on the ground glass, which is then held as 

 close as possible on the side towards the observer. 



If the jet be supplied from an insulated vessel, the coalescence of 

 colliding drops continues for a time after the removal of the in- 

 fluencing body. This is a consequence of the electrification of the 

 vessel. If the electrified body be held for a time pretty close to the 

 jet, and be then gradually withdrawn, a point may be found where 

 the rebound of colliding drops is re-established. A small motion to 

 or from the jet, or a discharge of the vessel by contact of the finger, 

 again induces coalescence. 



Although in these experiments the charges on the colliding drops 

 are undoubtedly of the same name, it appeared to me very improbable 

 that the result of contact of two equal drops, situated in the open, could 

 be affected by any strictly equal electrifications. At the same time an 

 opposite opinion makes the phenomena turn upon the very small 



