56 



BIOLOGICAL EFFECTS OF RADIATION 



the ZF-axes; and CB plotted (on transparent paper) on the rc^'-axes. 

 The second is laid over the first and shifted to that position where it is 

 found to fit the first. The difference d in the two filter thicknesses, for 

 corresponding points on the two curves, is given by the difference {x - x') 

 for the point C and is the magnitude sought. 



1.5 2.0 2.5 



Copper Filter MM 



FiQ. 8.— Superposition of copper absorption curves obtained with thick and thin tubes. 



Having outlined the general procedure, it will next be inquired if like 

 excitation potentials in the two tubes of Figs. 5 and 6 produce absorption 

 curves which are subject to the same correlation as curves CB and AB 

 (Fig. 4) just treated. In other words, is the radiation from the thick-wall 

 pyrex tube (Fig. 6) of the same quality as that from the thin-wall tube 

 (Fig. 5) after passing through some unknown thickness of copper? 



By taking the curves of Fig. 6 and fitting them as just described to the 

 curves of like excitation potential in Fig. 5, a very satisfactory correlation 

 is obtained. The curves of Fig. 8 are those of Fig. 5 reproduced; the 



