PROCEEDINGS 



OF 



THE ROYAL IRISH ACADEMY 



PAPERS READ BEFORE THE ACADEMY 



I. 



THE LARGE IONS IN THE ATMOSPHERE. 



By H. KENNEDY, M.A., M.Sc, University College, Dublin 



Read April 14. Published June 27, 1913. 



This paper is a continuation of a previous one 1 by Prof. McClelland and the 

 author dealing with observations of the large ions in the atmosphere. In the 

 previous work over 400 sets of observations were made of the number of 

 large ions per cc. at intervals over a period of more than a year. The 

 extreme values obtained were 3,700 per cc. and 60,000 per cc, the average 

 value being about 16,000 per cc. The observations were made at University 

 College buildings in Dublin, and it seemed to us that the number of large ions 

 might be very different in purer air at a distance from the city, in view of the 

 fact that large ions, which have the same mobility as those that occur in the 

 atmosphere, are found in gases drawn from flames of various kinds, when 

 sufficient time has elapsed after leaving the flame. The vast number of 

 sources of combustion in the city must produce great numbers of such ions, 

 and as, unlike the case of small ions, the time necessary for them to disappear 

 by recombination when once produced is very great, it seemed likely that the 

 atmosphere of the city must contain a great number of large ions artificially 

 produced. It was, therefore, desirable to make observations at some place at 

 a distance from the city. An opportunity of doing this was afforded through 

 the kindness of Prof. A. W. Conway, 2 who provided at his house in Dalkey a 

 room in which to set up the necessary apparatus. Dalkey is a small town 



1 Proc. Roy. Irish Acad., vol. xxx, Sec. A, pp. 72-91. 



2 I am also much indebted to Mr. J. M. Walsh of Dalkey for the use of his electrical 

 supply to charge the accumulators necessary for the observations. 



PROC. R.I. A., VOL, XXXII., SECT. A. [1] 



