406 Messrs. Wilson and Makower on the Rate of 



one pair of quadrants of an electrometer, the other pair of 

 which was permanently connected to earth. The vessel A 

 was 6*4 cms. long and 5 cms. in diameter, and its end 

 was closed by an aluminium-leaf which would allow the 

 a rays to pass through. The vessel B was 15*4 cms. long 

 and had a diameter of 8*4 cms., its end being closed by 

 a copper plate thick enough to absorb all the a. rays, but 

 thin enough to allow much of the /3 radiation to pass 

 through. 



A wire which had been exposed to the radium emanation 

 for a sufficient length of time to allow the deposit to assume 

 a steady state was broken in two pieces, one of which was 

 fixed outside the vessel B, the other being fastened to an iron 

 bar I which, by means of the screw S, could be moved towards 

 and away from the vessel A. The vessel A was connected 

 to one terminal of a battery of two hundred small storage- 

 cells, the middle point being connected to earth and the other 

 terminal to B. Two lead screens, L L, were made which 

 could slide so as to leave an opening between them, and were 

 placed close to the end of the vessel A. The distance between 

 the plates could be varied from the whole width of the vessel 

 to nothing. By altering the width of this opening and 

 varying the distance of the wire from the ionization-vessel A, 

 a balance could be obtained between the ionizations produced 

 in A and B by the two wires respectively. 



After removal from the emanation to which they had been 

 exposed, the wires were left for a sufficient length of time 

 to allow the radium A practically to disappear. The balance 

 was then made, roughly at first by means of the lead screens 

 and then more carefully by the screw S. In the earlier 

 experiments the difference of the ionizations produced in the 

 two vessels in one minute was measured at intervals of about 

 five minutes, the value of the ivhole ionization in the vessel B 

 also being determined from time to time. It was found that 

 the needle did not move uniformly from its position of rest 

 to its final position, but moved irregularly, as is often the 

 case when the difference between two nearly equal large 

 ionizations is being measured*. These irregularities could, 

 however, be to some extent eliminated by measuring the 

 difference of the ionizations produced in five minutes instead 

 of one minute. 



The results obtained in this manner for two distances D of 

 the wire from the vessel A, 7 cms. and 1*4 cms. respectivelyj 



* Bronson, Phil. Ma?. Jan. 1906. 



