920 Prof. H. A. Bumstead on Emission of Electrons 



electrode was about 13 percent, less than from the aluminium 

 but the variation with the speed o£ the a-rays was very nearly 

 the same. In the following table are given the averages for 

 all the experiments with both metals (with positive potential 

 on the case) ; the currents with 2 foils are called 100 as 

 before. Included in the table are two' series of ionization 

 measurements. These were made by removing the foil from 

 the electrode E, admitting a small quantity of air (pressure 

 •032 mm.), and charging the case positively. The first of 

 the two ionization measurements is with the aluminium leaf 

 on F and F', the second with the gold leaf. 



Table II. 



No. of Foils. 



Al 



Gold .. 

 Air(l) 



Air (2) ! 100 



! 2. 



3. 



4. 



5. 



6. 



100 



105-2 



117(5 



107-3 



39-1 



100 



1056 



1182 



115-6 



72-2 



100 



110-5 



134 



143 



573 



100 



110 



130 



143 



96-5 



As will be seen, the course of the series with the two metals 

 is nearly identical ; the differences in the last column are to 

 be attributed to the greater stopping-power of the aluminium 

 leaf ; it appears also in the two ionization experiments with 



CM. 

 4 



Fig. 4. 





























"~oS< 





"® 











' 



Y 







O ALU 

 X QQU 

 © AIR 



MINIUM 

 D 



f 















20 40 60 80 100 120 140 160 



the two metals on the ring F. Fig. 4 gives a graphical 

 reprsentation of these results; it is to be remembered, 



