202 PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 



ieuee ot'descrii)tion we sliall call this secoiid form ofeoiidcusatioii dense 

 condensation^ while that usually observed we shall call ordinary con- 

 densation. Xot that there is any hard and fast line between these two 

 forms, as the one may be made to change by imperceptible dej»rees 

 into the other. All that is meant is that the (Mie is dense compared 

 Avith the other. 



One result of this investigation is that in addition to electrification 

 of the jet, there are four other ways in which the ordinary condensa- 

 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 



dift'erent ways of causing the ordinary condensation to change and 

 take the dense form. In the exi^eriments 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 i)revent the irregularities which would be produced if the water 

 condensed in the pipe were allowed to issue from the nozzle. The noz- 

 zle generally used was made of brass, carefully bored to a diameter of 

 1"""., 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. Elect riji vat ion. — In the exi)eriments with electricity only steam of 

 a low i)ressnre should be used. The reason of this will be understood 

 from what follows under division 4. In these experiments slight electri 

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

 was available for the purjtose, and in the dam]) atmosphere produced 

 by the steam jet the electrificaticm was only capable of giving a spark 

 of about l*^^'". or generally less. 



The necessary condition for the electricity producing any effecton the 

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

 charge or by an induction discharge. The mere presence of an elec- 

 trified 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 



