582 



Sir E. Rutherford on Collision of 



oxygen gives rise to numerous bright scintillations which have 

 a range of about 9 cm. in air. These scintillations have about 

 the range to be expected if they are due to swift N or atoms, 

 carrying unit charge, produced by collision with a particles. 



Fig. 1. 



12 















\ \? 











\o 











^X<^ 











10 



14 18 22 



Absorption in cms. of stir 



26 



28 



All experiments have consequently been made with an ab- 

 sorption greater than 9 cm. of air, so that these atoms are 

 completely stopped before reaching the zinc sulphide screen. 

 It was found that these long-range scintillations could not 

 be due to the presence of water vapour in the air ; for the 

 number was only slightly reduced by thoroughly drying 

 the air. This is to be expected, since on the average the 

 number of the additional scintillations due to air was equi- 

 valent to the number of H atoms produced by the mixture 

 of hydrogen at 6 cm. pressure with oxygen. Since on the 

 average the vapour pressure of water in air was not more 

 than 1 cm., the effects of complete drying would not reduce 

 the number by more than one sixth. Even when oxygen 

 and carbon dioxide saturated with water vapour at 20° C. 



