from Ordinary Materials. 



537 



experimental curves we know c, d, />, 6, hence s and v 2 can 

 be calculated. The values found in this way are given in 

 Table I., columns 2 and 3. 







T. 



LBLE I. 











1 



Material. 



2 3 



Without Screen. 



4 



6 



7 8 



With Screen. 



Dimensions of Box. 



Lead 



sXlO* 



tfo X 10 5 



*'X10 1 



y 2 ' x 10 s 



cd. 



777 

 792 

 710 

 710 

 780 

 710 



c+d. Range. 



3-86 



33 



10 



0-8 



092 



2-04 



322 



092 



3-19 

 2-76 

 336 

 1-54 



3-84 



215 



1-0 



0-47 



00 



1-69 



1-31 



043 



0-88 



T33 



22 



0-83 



f>6-4 



21 



Tinfoil 



Aluminium. . 

 Zinc 



57-0 

 53-8 

 53-8 

 56-6 

 53-8 



20 

 22 

 20 

 21 

 22 



Platinum ... 

 Graphite ... 



§ 7. The curved portion of the trace requires further con- 

 sideration. In this region the distance between the sides is 

 so small, that the absorbable radiation is not wholly absorbed 

 in traversing the layer of air. and consequently does not 

 exert its full ionizing effect. For this part of the curve the 

 ionization due to each sq. cm. of the walls will be an ex- 

 ponential function of x and X, the absorption coefficient, say 

 /(./-. X). Of course 5 = f(y?,X). 



If we could determine the form of the function we could 

 determine X from the curve, but in order to do this we must 

 know the relation between the intensity of the radiation 

 emitted in each direction and the angle that direction makes 

 with the normal to the radiating surface. Thus, if the rays 

 were all projected normally, 



where I is the ionization caused actually at the surface, 

 the rays are emitted equally in all directions. 



If 



ft 



C 1 — t*-*' 



+ 



- . 



Ideally it would be possible to determine from the earlier 

 part of the curve the function applicable to the case and the 

 value of X for any metal. But actually it is not possible to 

 draw this portion with sufficient accuracy for the purpose ; 



Phil. Mag. S. 6. Vol. 9. No. 52. April \ ( J0:>. 2 N 



