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Mr. J. Aitken. On some Phenomena [Apr. 28, 



particles, and the condensation becomes dense. But if the nozzle 

 be not pointed, then the presence of the electrified body produces no 

 change, as there is no discharge of electricity. But if now we hold a 

 needle or other pointed conductor near the jet issuing from the 

 rounded nozzle it at once becomes dense, by the induction discharge 

 from the point. In place of a point in the last experiment, we may 

 use a flame ; in fact, we may use any influence which will enable the 

 electrified body to electrify the particles in the jet. 



Another way of making this experiment is to insulate the boiler, 

 and electrify it. If the nozzle be pointed, the jet becomes dense on 

 electrification ; but, if it be rounded, the electrification has no effect. 

 If, however, we bring a needle or aflame near the rounded nozzle, the 

 jet becomes dense. To get no effect from the electrification it is neces- 

 sary that the nozzle be a ball of some size, the orifice through which 

 the steam issues being, of course, the same diameter as that of the 

 pointed jet. 



The effect of the electrification has been studied by R. Helmholtz 

 and by Mr. Shelford Bidwell,* but neither of them seems to be satis- 

 fied with any explanation they offer. Mr. Bidwell, from a spectro- 

 scopic examination of the light transmitted through the jet under the 

 two conditions, came to the conclusion that in the dense condition the 

 particles were larger than in the ordinary form of condensation ; and 

 he thinks that the increase in size is due to the electricity causing 

 the small drops of water to coalesce and form larger drops. In 

 support of this explanation, he quotes Lord Rayleigh's experiments 

 on the coalescence of drops in water jets while under the influence of 

 electricity. As Mr. Bidwell does not put forth this opinion as final, 

 there is less reason for hesitation in stating that the conclusion I 

 have come to is diametrically opposed to Mr. Bidwell's. 



There seems to be no doubt that electricity will act on these very 

 small drops of water in the same way as it acts on the drops in a jet 

 of water. That its action is similar is easily proved by the following 

 experiment with mist drops : — Take a small open vessel full of hot 

 water — it is better to colour the water nearly black for convenience 

 of observation — a cup of tea without cream does very well for the 

 purpose. Place the cup on a table between the window and the 

 observer. On now looking at the cup from such a position that no 

 bright light is reflected from the surface of the liquid, there will be 

 seen what looks like scum on the surface of the tea. That scum is, 

 however, only a multitude of small mist-drops which have condensed 

 out of the rising steam and have fallen on the surface of the liquid, 

 where they are seen floating. If now we take a piece of brown paper, 

 or any convenient material, and rub it slightly and hold it over the cup, 

 the " scum " will disappear at once, and be replaced by other drops 

 * < Phil. Mag.,' February 1890. 



