856 Ionization in Gases. 



Table II. 



V 40 260 



Copper 26-6 1160 



Zinc 1-07 44«2 



Ratio 25 26-2 



(The units in Table II. are not the same as in Table I.) 



Thus with the same external source o£ light the ratios of 

 the currents obtained with different forces are practically the 

 same. It was difficult to maintain the light at constant 

 intensity, and the differences between the radios do not 

 exceed the differences due to this cause. 



The results in Table II. are especially striking. For 

 Y = 40 there is practically no ionization by collision, and 

 V=260 therefore magnifies the initial ions produced by the 

 factor 40 ; yet this magnification is nearly exactly the same 

 for both copper and zinc electrodes, whose photo-electric 

 activities are widely different. 



5. A few experiments were made with the iron plate 

 comparing it with zinc, including one at a high pressure. 



The iron was about four times as active as the zinc, and 

 the results for various voltages V and pressures p, in mm. of 

 mercury, are given in Table III. 



Table III. 



p -6 1-4 47 4-7 150 



Y 80 120 120 240 80 



Eatio 3-85 3'76 3-8 3*8 3"6 



For p = 150 and V = 80 there is no measurable ionization 

 by collision, and the currents were so small that it was not 

 easy to get their ratio accurately. 



All the above experiments combine to show that any 

 ionization due to radiation from the gas is negligible com- 

 pared to the ordinary ionization by collision of Townsend's 

 theory. 



The above experiments were conducted in the laboratory 

 of Professor Townsend, at whose request they were under- 

 taken and to whom I am indebted for advice and assistance. 



