1892.] 



connected ivith Cloudy Condensation. 



411 



when the electrified body is removed. As in Lord Rayleigh's experi- 

 ments, a very feeble electrification is sufficient to cause the absorption 

 of the drops into the body of the liquid. It is therefore not because 

 there is supposed to be any difference in the action of electricity 

 on large and on very small drops that a different conclusion from 

 Mr. Bidwell's has been arrived at, but because all the experiments to 

 be described point to the conclusion that the dense form of condensa- 

 tion is not due to an increase in the size of the drops, but to an 

 increase in the number, accompanied of course by a diminution in 

 the size. 



We may suppose the following to be something like the manner in 

 which the electricity acts on the jet : — In a steam jet the rapid move- 

 ments of the drops give rise to frequent collisions, and these result in 

 the coalescence of many of the drops, so that each drop in ordinary 

 condensation is made up of a number ; but, when the jet is electrified, 

 the electrification prevents the particles coming into contact, as they 

 repel each other, and the consequence is, we have a greater number 

 of particles in a dense and electrified jet than in an ordinary one. 



Lord Rayleigh's experiments on the action of electricity on water 

 jets support this view. He has shown that, in order to produce 

 coalescence, the electrification must be very slight, and he also points 

 out that the coalescence does not seem to be so much due to electrifi- 

 cation as to a difference of electrification, which would appear to 

 cause a discharge of electricity to take place between the drops, 

 which ruptures the films, so causing contact. Further, he has shown 

 that when the electrification is strong, and the conditions are such 

 that the drops become electrified, the effect is diametrically the 

 opposite, and instead of coalescence, the particles now scatter far 

 more than the unelectrified drops. Now from the conditions of the 

 experiments with electrified steam jets it is evident that the drops are 

 electrified, and are in the same condition as the electrified scattering 

 water jet. We are, therefore, entitled to expect that the electricity 

 will prevent and not aid the coalescence of the small drops in the 

 steam jet. 



Other considerations also point to the increase in the density of the 

 jet being due to an increase and not to a diminution in the number of 

 drops. We know that if we blow steam into air, that the fewer dust 

 nuclei there are in the air, the thinner is the condensation, and when 

 the dust is nearly all out of the air, only a fine rain falls which can 

 scarcely be detected by the unaided eye: Further, the evidence from 

 condensation produced by expanding moist air points to the same 

 conclusion, namely, that the more dust particles there are in the air, 

 the denser is the condensation when cooled by expansion, and the 

 purer the air is, the thinner is the cloud.* These experiments all 



* ' Trans. Roy. Soc. Edinburgh,' vol. 30, Part I, p. 340. 



