659 



Physics. - - "A neio electrometer, specialii/ arranged for radio-active 

 investiqations" . Part I. By Miss H. J. Folmkr. (Communicated 

 by Prof. H. Haga). 



(GommunicatL'd in the meeting of May 30, 1914). 



Introduction. 



In trying to find an accurate method for measurements of the 

 natural ionisation of air in closed vessels, radio-active radiation of 

 the elements, etc., researches in which very small ionisation currents 

 are to be measured, it seemed to me that the need is felt of an 

 electrometer, which, besides possessing a great sensibility of charge, 

 will also be able to measure \ery minute currents with accuracy. 



As to the mentioned conditions, the latter is fulfilled by C. T. R. 

 Wilson's electroscope (the gold-leaf type), which owes this favour- 

 able quality to the very simplicity of the system; this namely renders 

 it possible to bring about the ionisation which is to be measured, in 

 the air contained in the apparatus itself, to avoid connecting wires, 

 together with electrostatic and other influences, the disturbance 

 caused by insulators being confined to that of a single one. In my 

 opinion this is the reason that this electroscope is generally preferred 

 for various measurements requiring great accuracy to say a sensitive 

 DoLEZALEK electrometer, which lacks these advantages, notwithstand- 

 ing the fact of a much greater sensibility of charge óf the latter ; 

 in consequence of this sudden changes in the natural ionisation of 

 air in closed vessels, for instance, the existence of which is accepted 

 by many investigators, cannot manifest themselves clearly when the 

 electroscope is used ; moreover measurements of small currents will 

 take much time. 



This has led me to construct an electrometer, the principle and the 

 method of working of which I shall discuss in what follows, and 

 which in my opinion can supply the mentioned need. It appeared 

 from the results obtained, that with this apparatus currents can be 

 measured both very accurately and very sensitively ; accordingly 

 it seems to me, that for these reasons the apparatus may be very 

 suitable for various radioactive researches requiring the above 

 mentioned qualities, as was also corroborated by experience. 



Description of the yrincijjle of the apparatus. 

 In the figure a schematic representation of the arrangement is given ^); 

 the apparatus consists of: 



^) An accurate description of the apparatus will follow in a 2nd communication. 



