PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 205 



the air is the tliiuner is the cloud.* These experinieiits all point to 

 the conclusion that the dense form of condensation is due to a large 

 number of water drops, and the thinner form to a smaller number, 

 though of greater individual size. The only condition under which it 

 seems probable that tbe increase in number will not give rise to 

 increase in density is when the particles are so small that they are 

 unable to retle(.'t waves of any color of light. So far as has yet been 

 observed, this never happens. However slight the amount of expan- 

 sion, the greater number of particles always gives the denser form of 

 condensation. 



The action of the electricity on the jet does not appear to be any- 

 thing positive; it rather seems to prevent something which takes place 

 under ordinary conditions. For instance, electricity has no effect in 

 thickening the cloud of so-called steam rising from a hot and wet sur- 

 face. The electrically driven current of air from a point when directed 

 to the steaming suri^iee has no effect whatever on the density of the 

 condensation. Nor has electricity any effect (m the steam rising from 

 an open vessel. The small drops of water under these conditions move 

 but slowly, and there is but little tendency for them to come into col- 

 lision with each other. There are therefore few collisions for the elec- 

 tricity to prevent, and little or no thickening is produced by electrilica- 

 tion under those conditions. Further on we shall have frequent oppor- 

 tunities of seeing that the dense form of condensation is the result of 

 an increase in the number of particles, and that whatever gives rise to 

 an increase in the number causes an increase in the density. 



When the jet is electrified and becomes dense, it has been noticed 

 by others that it emits at the same time a peculiar sound, and I find 

 that whenever the jet becomes dense, from whatever cause, it begins 

 "to speak." But when the density is due to electrification, the sound 

 is slightly different from the sound emitted when dense from any 

 of the other causes. When dense from cause other than electri- 

 fication, the sound is similar to that produced by the jet striking an 

 obstruction; but when electrified, the sound is a combination of this 

 sound with another due to tlie discliarge of the electricity, and this 

 second sound depends on the manner in which the electric discharge 

 takes place. If the discharging point is not sharp, and the potential 

 is just sufficient to cause discharge, then the discharge is not continu- 

 ous, but takes place at short intervals. It becomes, in f^ict, a series 

 of disruptive discharges, and gives rise to a tluttering noise. This 

 rtuttering sound is greatly increased if the ])oint terminates in a small 

 ball of about 1 millimeter diameter, and it is entirely abolished if we 

 use a very sharp point, or better, a llame. The discharge with either 

 the very sharp i^oint or the flame is perfectly continuous, and nothing 

 but the slight hissing that accompanies all dense forms of condensa- 

 tion is heard when the jet is electrified. 



Trans. Roy. Soc, Edinburgh, vol. xxx, Part i, pp. 340. 



