[379] 



XV. On the Electricity of R'lin and its Origin in TJmnderstorms, 



By GEORGE C. SIMPSON, D.Sc. 

 Communicated by DR. GILBERT T. WALKER, F.R.S. 



(Received January 6, Read February 11, -Revised April 14, 1909.) 



SINCE FRANKLIN first showed that thunder and lightning are caused by electrical 

 discharges, there have been numerous theories to account for the production of 

 electricity in thunderstorms, but none has been generally accepted by meteorologists. 

 When attacking the problems of thunderstorm electricity, two methods naturally 

 present themselves : we may either investigate the actual phenomena in the 

 atmosphere, or try to repeat on a small scale in the laboratory the processes which 

 may be supposed to take place during thunderstorms. During 1907-8 an 

 investigation was undertaken on both these lines at the Meteorological Office of the 

 Government of India in Simla. A systematic record was obtained by automatic 

 instruments of the electricity brought down by the rain during practically the whole 

 of one rainy season, and laboratory experiments were made to find the origin of the 

 electricity of thunderstorms. The work has resulted in the formation of a new 

 theory, which appears to account in a satisfactory manner for the electrical effects 

 observed during thunderstorms. 



The following paper is divided into three parts : Part I deals with the 

 measurements of the electricity of the rain, Part II with the laboratory experiments, 

 and Part III contains the new theory based on the results detailed in the previous 

 parts. 



PART I. Measurements of the Electricity of the Rain. 



The electricity brought down by rain had previously been measured by ELSTER 

 and GEITEL* in Wolfenbiittel, by GERDiENf in Gottingen, and WEISSJ in Vienna. 

 The apparatus used in Simla differed from the form used by each of these in several 

 particulars, chiefly in that it was entirely self-registering and was kept constantly 

 in action during the whole of the rainy season, whether precipitation was expected 

 or not. 



The final form of the Simla apparatus is diagrammatically shown in fig. 1. 

 A corrugated iron hut, 8 feet square, was erected on a suitable site in the grounds 



* ELSTEK and GEITEL, 'Wien. Ber.,' vol. 99, Abth. II. a, p. 421, 1890; 'Terr. Magn.,' vol. 4, p. 15, 

 1899. 



t GERDIEN, 'Phys. Zeit.,' vol. 4, p. 837, 1903. 

 t WEISS, 'Wien. Ber.,' vol. 115, Abth. II. a, p. 1285, 1906. 

 VOL. CCIX. A 455. 3 C 2 12.8.09. 



