PROCEEDINGS 



OF THE 



A self-recording electrometer for Atmospheric Electricity. By 

 W. A. Douglas Rudge, M.A., St John's College. 



[Received 18 October 1915.] 



In the course of the writer's work on the local variations of the 

 atmospheric potential gradient, the need was felt for a simple self- 

 recording electrometer. Most of those in use are costly and at the 

 same time rather elaborate in construction. A new arrangement 

 has therefore been devised which has answered the purpose in view, 

 and as the apparatus may be useful in other directions a description 

 is now given. 



It has been shown* that very considerable variations of the 

 normal potential gradient are produced by clouds of dust raised by 

 the wind, etc. ; and also by clouds of steam escaping under pressure 

 from steam boilers f. These variations are very sudden and do not 

 last for a long time, so that an instrument used for recording them 

 must be fairly quick acting. After a considerable amount of 

 preliminary work, the type of instrument adopted was a modified 

 form of the quadrant electrometer, the record being photographed 

 upon a piece of bromide paper attached to a revolving cylinder. 

 One special use to which the electrometer was to have been applied 

 was to find the relation between the potential gradient and the 

 altitude of the place of observation, and for this purpose it was 

 proposed to construct ten or more instruments, so that a number 

 of observations could have been carried out simultaneously. Some 

 work of this kind has already been done in South Africa from 

 which it appears that the potential gradient near to the ground 

 diminishes with the height of the place of observation above sea 

 level;]:. In order to get satisfactory results it is necessary for the 



* Proc. Roy. Sor. A, Vol. 90. t Proc. Pflij. Soc. A, Vol. 90. 



J Trans. Poy. Soc. SnntJi Afrirn, Vol. vi, pai-t 5. 



VOL. XIX. PT. I. 1 



