22 Dr. N. Bohr : Theory of Decrease of Velocity of 



ranges in air o£ the a-rays, when entering the absorbing 

 sheets, varied in these experiments from about 5 to about 

 2 cm. The figures in the table below for the absorption 

 relative to air are obtained by interpolation in Taylor's 

 Tables II. and III. (loc. cit. pp. 608-610), the range quoted 

 is the mean value of the ranges for the a-rays entering and 

 leaving the absorption sheets, and the values for the absorp- 

 tion are the mean values calculated from the different series 

 of experiments using same absorbing material. 



Range in air 



2-24. 



4-87. 





Hydrogen 



Air 



0267 

 100 



1-69 . 10 3 

 2-33 . 10 3 

 4-71 . 10 3 

 3-06 . 10 3 



0-224 



100 



1 75 . 10 3 



2-56 . 10 3 

 5-57 . 10 3 

 3-53 . 10 3 



i 



Aluminium 



Tin 



i 



Gold 



Lead 





The ranges 2*24 and 4*87 are chosen as those corresponding 

 to the velocities 1*35. 10 9 and 1*75. 10 9 according to the 

 formula (5). According to the same formulae we further 



dY 



get that for these velocities, -=- in air is equal to respectively 



— 2-01 . 10 8 and -1*20 . 10 8 . From this we get by help of 



dY 

 the above table the following values for — — : 



ft dx 



Velocity 



1-35 . 10 n 



1-7/i 109 







Hydrogen 



5-4 . 10 7 

 201 . 10 8 

 3-4 . 10 u 

 4-7 . 10 u 

 9-5 . 10 11 

 6-1 . 10 u 



2-7 . 10 7 

 1-20 . 10 s 

 2-1 . 10 n 

 3-1 . 10 11 

 6-7 . 10 u 

 4-2 . 10 11 





Aluminium 



Tin 



Gold 



Lead 



Hydrogen. 



Comparing the above values with the theory, we shall 

 start with hydrogen as the substance for which the assump- 

 tions mentioned on p. 20 are satisfied in the highest decree. 



