﻿Production of Condensation Nuclei in Air. 



819 



Thus, if — is the mean free path for 1 mm. pressure, Y 



the least potential difference between the ends of a path to 

 cause a negative ion to acquire sufficient velocity to generate 

 others by collision, then when p = 1 



NT 

 a = N<?~ X. 



The agreement of the as found with this formula for the 

 values N = 2'8, V = 12*3, is given below. 



Table XII. 



X 



200 



1G0 



120 



80 



40 



20 



a. found experimentally ... 



. XV 

 Ne X 



2-37 

 2-35 



2-27 



2-26 



2-1 

 21 



1-83 



1-82 



107 

 1-18 



•57 

 •50 





This value of V is also lower than for any other gas, the next, 

 among those examined, being hydrochloric acid for which 

 V=16*5 volts. For air it is 25 volts. 



In conclusion, we wish to express our thanks to Prof. 

 Townsend for valuable advice during the course of the 

 experiment. 



LXXX. Remarks on the Production of Condensation Nuclei in 

 Air and in Vapours by Intense Cooling and by Ultra- Violet 

 Light. 



To the Editors of the Philosophical Magazine. 



Gentlemen, — 



N connexion with the paper by Mr. Gwilym Owen which 

 appeared in the Philosophical Magazine for October, 

 1911, p. 563, entitled "Note on the Production of Nuclei in 

 Air by Intense Cooling," I should like to lay before you 

 some considerations which seem to explain the results there 

 obtained. These considerations are based on a series of 

 experimental researches on allied subjects which I carried 

 out together with Professor P. Lenard *. 



* P. Lenard and C. Ra 



Ueber die Wirkungen sehr kurz- 



welligen ultravioletten Lichtea auf Gase und iiber eine sehr reiehe 

 Quelle dieses Lichtes," Heidelberger Akademie. Five Parts: I. Aug, 2, 

 19.10; II. Nov. 5, 1910; III. Dec* 20, 1910; IV. June 9, 1911 ; V. Aug. 4. 

 1911. 



Phil Mug. S. 6. Vol. 2?,. No. 137. May 1912. 3 iv 



