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LV. On the Change of the Colours of Cloudy Condensation 

 with the Number of Available Nuclei, and on the Effect of 

 an Electric Field. By C. Barus*. 



1. fTlHE steam-tube f in which an ordinary jet is used to 

 A produce the colours of cloudy condensation has two 

 disadvantages, inasmuch as in the first place the quantity of 

 steam issuing at a given pressure cannot be varied, and in 

 the second place the manner in which the nuclei are brought 

 into the jet is not easily understood. One is not sure that 

 the whole of the " dust " J is active in producing condensation 

 when the charged air comes in contact with the jet from 

 without. Again, the colours of a relatively high order are 

 best, seen at relatively low temperature and pressure, and 

 require a large volume of steam if they are not to be too 

 faint for recognition. Both desiderata are met in the follow- 

 ing device, in which the steam flux is annular, the air influx 

 axial, and which has the final advantage of making the jet 

 more easily accessible ; for the saturation of colours even of 

 high order is now such that the lower window and lateral 

 influx of charged air may be dispensed with . 



The body of the jet (fig. 1) is of a bullet-shaped pattern,. 



Fig. 1.— Section of Steam- Jet, Scale 1/2. 



* Communicated by the Author. 



t The present paper is a continuation of my earlier experiments given in 

 this Magazine [o] xxxviii. pp. 19-35 (1894). The old apparatus referred to- 

 is there described, together with the conditions under which colours are 

 obtained. The new series of researches with the steam-jet (a brief 

 account of which will be given in this and subsequent papers) were made 

 possible by a grant from the Smithsonian Institution, and are published 

 by permission of the Secretary. 



X I shall continue to use the antiquated term " dust" for convenience. 



