Duarie — Emission of Electricity. 11 



19. Experiments were made to measure the ratio between 

 the charge carried by the rajs from the induced activity and 

 the charge carried by the maximum number of ions that can 

 be produced in air by the same induced activity when all the 

 a rays are absorbed in the air. As the latter is several thou- 

 sand times the former, it is better to measure the ratio in two 

 steps. In the first step, with the electrode A in the tube i?, 

 the ratio between the currents at atmospheric pressure and in 

 a liquid air vacuum was measured, and in the second, with a 

 smaller amount of activity, the ratio between the currents 

 with the electrode in the tube, and in a larger condense]*, was 

 measured, both at atmospheric pressure. The product of the 

 two ratios is the ratio required. 



20. For the first step, the brass electrode having been made 

 radio-active as before, it was placed in position in tube B and 

 currents measured with the piezo-electric quartz at atmospheric 

 pressure. Then the tube was rapidly exhausted by opening a 

 stop-cock communicating with the reservoir containing carbon 

 cooled to the temperature of liquid air, and the currents meas- 

 ured again. The electromotive force each time wa's 2*2 volts 

 (i. e. a 50 volts per cm.). The data appear in Table IT. 

 Making the small corrections for the decay of the activity, we 

 find for the ratio of the currents in air to that in vacuum, 61 

 for t = 13, and 69 for t = 64. Other experiments gave values 



Table IV. 



Time Positive Current 



10 52*5 ) w , . 



,, _, j- Atmospheric pressure 



13 

 14 

 60 21-0 ) 



0-82 ) T . •-,. 

 „o y Liquid air vacuum 



~, - Atmospheric pressure 

 61 0-322 Liquid air vacuum 



ranging from QQ to 70 for 60 to TO minutes after the electrode 

 had been removed from the emanation. Earlier than this the 

 ratio is smaller, owing undoubtedly to the fact that there is 

 then proportionately more radium B on the electrode. 



21. To measure the ratio of the current in the tube B at 

 atmospheric pressure and the saturation current when all the 

 a rays produce ions in air, a large cylindrical condenser was 

 constructed 19'8 cm long and 17*9 cm in diameter. A rod of 

 brass suitably insulated held the electrode A at the center of 

 the condenser, and at the same time acted as the electrode. A 

 verv much smaller amount of induced activity than before 



