29 



could pass into the chamber only for a short period during 

 the motion of the pendulum. The pendulum at the same 

 time operated a contact Kr^ by means of the pin L^, and this 

 operation connected the electrode, C, to a high potential de- 

 rived from the small accumulator cells, T, joined in series 

 with a high resistance, R. Prior to the movement of the 

 pendulum these cells were connected to earth through the 

 key, /i,. A second pin, L^, attached to the pendulum, oper- 

 ated another key in such a way as to complete an auxiliary 

 circuit which released a second pendulum at a definite in- 

 stant. This second pendulum, after an interval of 1.25 sec, 

 operated a second relay, which connected the electrode, G , to 

 earth by means of the key, K^. 



The pins, L^ and L^, could be set in any position upon 

 the pendulum, and by this means the field between the elec- 

 trodes, C and D, could be applied at any definite instant 

 during the swing of the pendulum, and removed after always 

 the same lapse of time, viz., 1.25 sec. With the range of 

 field strength employed, this time was sufficient to allow for 

 the collection of all the ions which had been produced by the 

 o particles crossing the chamber. 



The distance between the electrodes, C and D, was ad- 

 justable. To make the effects of ordinary recombination small 

 it was advisable to keep the distance between C and D small, 

 but as this decreased the volume of gas which could be ion- 

 ized, it was found necessary to work with a distance between 

 the electrodes of I'S cm. 



To perform an experiment, the pendulum, having been 

 drawn to one side and held by means of a catch, the lead 

 plate, TI, was set so as to screen the chamber from the radium, 

 the keys, K, K^, K^, being closed, make contact to earth, the 

 key A'g, being left open. The second pendulum was drawn 

 aside and held in position by a clutch. The condenser wias 

 closed. By means of electromagnets the main pendulum is 

 released, and at the same time the key K raised. The pin, 

 L, is set so that the gauze, C, is not electrified until the lead 

 screen, //, again shuts off the radium ; L^ and L^ then strike 

 their keys respectively at the same instant ; C is thus electri- 

 fied, and the second pendulum set swinging. The first pen- 

 dulum is caught at the end of its swing. When the second 

 pendulum has accomplished its swing it causes the key, E^, to 

 be closed, and the gauze C is thereby connected to earth. 



A constant interval of 4 sec. was now allowed befo-re 

 opening the condenser, (S' — this for each reading — and at the 

 end of that time the electrometer was disconnected from 

 earth by K, and the key, K, closed. The charge communica- 

 ted to the electrometer was measured in t-erms of the first and 



