28 THE ROYAL SOCIETY OF CANADA 



tube s.s. which could be slid down over the electrical system. The 

 use of this sliding tube was to limit the volume from which ions could 

 be drawn to the fibres to as low a value as possible. With this tube 

 raised the effective volume as given by the makers was 2021 •! cc, but 

 with it lowered the effective volume was only 31 -5 cc. 



The fibres were illuminated by light thrown into the instrument by 

 a mirror through a window, and the readings were taken with a micro- 

 scope piovided with a scale. The air in the receiver was kept dry with 

 a small quantity of sodium carried in a small receptacle attached to the 

 body of the instrument. The electrical system in practice was charged 

 by means of a Zamboni pile through the intermediary of an insulated 

 metallic sound which passed through the case and which could be turned 

 when desired so as to come into contact with a metal piece which con- 

 nected the fibres to their upper insulating support. All the openings into 

 the receiver, with the exception of the covering tube A were either closed 

 by soldered contacts or by fluted joints provided with leather washers. The 

 lower end of the covering tube A had a ground conical surface and when 

 in position was held hermetically connected to the body of the instrument 

 with a shoulder piece provided with a thread. The instrument was pro- 

 vided with a covering tube for the microscope and a cover plate for the 

 window. Both of these could be screwed tightly against leather washers. 



When all the openings into the receiver were carefully closed the 

 instrument was both water-tight and air-tight. 



The electrical system was calibrated in the ordinary way and by 

 means of a calibration curve the readings were transcribed from changes 

 in deflections into potential falls. 



The capacity of the electrical system was 1*04 cm. 



The theory of the instrument is as follows — 



Let Q be the loss of charge observed in one second and A the part 

 of Q due to the leak over the insulating supports. 



Let V be the effective volume with the tube s.s. up and V^ its 

 effective volume with the tube down. 



Then Q = A -I- BV where B is a constant 



and Qi = A + BVi 



VQ, - V.Q 



or A = 



V-V, 



V V . * 



= Q, pQ ifrr^is a small quantity. 



The charge on the ions generated per cubic centimetre per second 

 is then given by 



B = Q~Q ^ 



