4 Dr. G. C. Simpson on the 



nozzle a cylindrical metal tube, 1^ cm. wide, was fixed so 

 that the orifice of the sprayer was in the middle o£ the tube. 

 The sprayer and tube were connected to earth, thus pre- 

 venting any electrical field acting on the nozzle and so 

 charging the drops by influence. 



" By this arrangement a large proportion of the spray 

 was reflected from the water surface. Above the spray- 

 cloud was suspended an insulated sphere, of 2 cm. radius, 

 which could be connected at will to the positive or negative 

 pole of a Zamboni pile having 2000 pairs of plates. It was- 

 then found that when the sprayer was in action the insulated 

 vessel containing the reflecting water surface took on a 

 charge which was of the same sign as the charge on the 

 metal sphere. The charge was so large that it could not be 

 read by the telescope and scale. At the same time the spray 

 was found to carry a charge of the opposite sign. From the- 

 latter fact we see that there was no transference of charge 

 from sphere to surface through the spray-cloud. The spray 

 particles bouncing from the water surface acted exactly like- 

 the drops in a Thompson ' water dropper'' and tbe vessel 

 containing the water surface like the collector itself. This,, 

 however, was only possible if the bouncing drops came into 

 electrical contact with the water surface. " 



Elster and Geitel's explanation of this experiment was the 

 only one possible in 1885, but a much more reasonable one 

 is obvious now. As shown by Eve * and others, when water 

 is sprayed in the manner described the air in the blast is 

 highly ionized. Thus in the experiment the fine water 

 particles were carried along in a stream of ionized air. 

 When this stream came into the strong electrical field 

 between the positively charged sphere and the water surface,, 

 the positive ions were driven into the latter, and part of the 

 excess of negative ions became attached to the spray particles. 

 The reverse happened when the sphere was charged nega- 

 tively. This explanation accounts for the facts without 

 supposing any rebounding of water-drops. In fact the 

 result would have been the same if all the drops could have 

 been removed before the air-blast came into contact with the 

 water surface. 



When one considers that the cause of a drop bounding 

 from a water surface is the film of air between the two, it is 

 difficult to see how electrical contact could take place until 

 this layer has been removed and the two surfaces joined up. 

 In this connexion it maybe pointed out that C. R. Englund f 

 * Eve, Phil. Mag. [6] xiv. p. 382 (1807). 

 t Englund, Phil. Mag. xxvii. pp. 457-458, March 19] 4. 



