542 Mr. -K. R. Campbell on Radiation 



In what follows we shall calculate all quantities on the 

 assumption that the rays are ejected normally ; we shall 

 thus get a qualitative description of the phenomena which 

 will not be quantitatively correct. We will give one set of 

 readings to exemplify each method. 



Method 1. — Tin-plate: window '00033 cm. of aluminium. 



log e 1000I. > _ log g I 1 -log g I 2 | 



3 ' 04 > o'P 



2 ' 89 > 0-72 



2*71 



1 {1 > 0-66 



2-08 



Mean 0*66 



The value of A obtained by moving the plate from to 

 •5 cm. was always abnormally small and therefore rejected. 



Method 2. — Lead. 



1= increase of I' = increase with 



leak through one log e 10G0 I. two leaves over log^.1000 1'. >V(A1)* A(air)* 

 leaf over window. window. 



•023 3-14 -0095 2-23 2700 1-3 



The increase given by zinc and aluminium was too small 

 to be measured by this method. 



Distance of plate 

 from window =x. 



Increase of 

 leak = I. 



0*5 cm. 



•021 



0-75 „ 



•018 



1-00 „ 



•015 



1-50 „ 



•008 



Method 3.— Lead. 



Window covered by Window covered by 

 foil -00033 cm. thick, foil -00053 cm. thick. 



X'(A1). X(air). 



I = -023 r=*014 2500 1*18 



In the first column of Table III., column 1, are given the 

 values of X deduced from the curves by a simple geometrical 

 method on the assumption that all rays are projected nor- 

 mally ; in columns 2, 3, 4 are given the values found by 

 methods 1, 2, and 3 above. In Table IV. the increases which 

 should be caused by the various materials placed outside the 

 window are calculated on the same assumption and compared 

 with those actually found. 



§ 12. The agreement in Table III. and in Table IV. is only- 

 qualitative ; but it must be remembered that the assumption on 

 which the figures are calculated is almost certainly incorrect. 



* The absorption coefficients for air and aluminium are compared 

 throughout on the assumption that they are proportional to the densities 

 of those substances. 



