1892.] 



connected with Cloudy Condensation. 



409 



tion may be changed into the dense form. These five ways of 

 changing the ordinary into the dense form of condensation are : — 



1. Electrification of the jet. 



2. An increase in the number of dust nuclei. 



3. Cold or low temperature of the air. 



4. High pressure of the steam. 



5. Obstructions in front of the jet and rough or irregular nozzles. 

 We shall now describe some experiments to illustrate each of these 



different ways of causing the ordinary condensation to change and 

 take the dense form. In the experiments to be described, the steam 

 was generally generated in a copper boiler, which could be pressed 

 up to fully one atmosphere. The nozzle from which the steam 

 escaped was placed at some distance from the boiler to prevent the 

 hot gases influencing the jet. The steam was conveyed by means of 

 a metal pipe to the nozzle, and a water trap was placed near the end 

 of this pipe to prevent the irregularities which would be produced if 

 the water condensed in the pipe were allowed to issue from the nozzle. 

 The nozzle generally used was made of brass, carefully bored to a 

 diameter of 1 mm., the diameter of the bore widening inwards, while 

 the outside of the nozzle was turned to a fine edge in front. With 

 this apparatus most of the experiments were made, but occasionally 

 glass vessels and nozzles were used, as well as vessels and nozzles of 

 other materials, but with no marked difference in the results. 



1. Electrification. 



In the experiments with electricity only steam of a low pressure 

 should be used. The reason of this will be understood from what 

 follows under division 4. In these experiments slight electrification 

 was used, as only an old-fashioned cylinder electrical machine was 

 available for the purpose, and in the damp atmosphere produced by 

 the steam jet the electrification was only capable of giving a spark of 

 about 1 cm. or generally less. 



The necessary condition for the electricity producing any effect on 

 the jet is that the particles in the jet be electrified either by direct 

 discharge or by an induction discharge. The mere presence of an 

 electrified body near the jet has no influence whatever. In order 

 that it may have an effect, the electrified body must terminate in a 

 point placed near the jet, and the potential must be great enough to 

 cause a discharge of the electricity to the jet. When this takes 

 place the jet at once becomes dense and remains in that condition 

 while the discharge continues. The electrified body may, however, 

 electrify the jet by induction. If, for instance, the electrified body 

 be a sphere, and the nozzle from which the steam is issuing be 

 pointed, the electricity discharged by the nozzle will electrify the 



