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V. 

 THE LARGE IONS IN THE ATMOSPHERE. 

 By professor J. A. McCLELLAND, D.Sc, F.R.S., 



AND 



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



Read June 24. Published Decrmker 1 1, 1912. 



In recent years much work has been done in the study and measurement of 

 the ions in the atmosphere. In practically the whole of this work, however, 

 atteiltiou has been devoted solely to ions similar to those produced directly 

 when a gas is subjected to an ionising agent, and having a mobility of the 

 order of 1'6 cms. per second in an electric field of 1 volt per cm. Although 

 Langevin,* in papers published in 1905, drew attention to the existence in the 

 atmosphere of another class of ions of much smaller mobility and even more 

 niimerous than the ordinary ions, work on atmospheric ionisation has 

 continued to deal solely with the ordinary ions. 



Langevin showed that these large atmospheric ions have a mobility of the 

 order of -joVo cm. per second as compared with 1-6 cm. per second for the 

 ordinary ions, and that they are about fifty times more numerous than the 

 ordinary ions. Further, the theory of the production and nature of these 

 large ions developed by Langevin suggests that they are probably of great 

 importance in general meteorological theory. The only other detailed 

 investigation of these large atmospheric ions is that of Pollockf and LusbyJ 

 at Sydney in 1909 ; aud their results, while giving a smaller number than 

 Langevin's for the large ions per c.c, agree in showing their general occurrence 

 and importance. 



The object of the present investigation is to obtain further data regarding 

 the number of these large ions in the atmosphere, and their origin and 

 properties. Further reference to the important work of Langevin and of 

 Pollock and Lusby will be deferred until we are discussing the observations 

 recorded in this paper. 



*Comptes Rendus, 190.5, cxl, pp. 232-234: Le Radium, 1907, p. 218. 



tPioc. Roy. Soc. N.S.W., 1909, pp. 61-68, and pp. 198-203, Science, 19.09, pp. 919-92S. 



JProc. Roy. Soc. N.S.W., 1909, pp. 5.5-60. 



