318 



BELL SYSTEM TECHNICAL JOURNAL 



Another series of photographs, in I'"ig. 8, shows the two scattered 

 rays produced when a beam of the A'a-radiation of inoK bdenum falls 

 upon various scattering substances: carbon (the sixth element of the 

 periodic table), aluminium (the thirteenth), copper (the twenty-ninth), 

 and silver (the forty-seventh). The relative intensity of the two 

 rays — that is to say, the proportion between the number of quanta 

 which rebound as from free electrons, and ilie nuinlier of quanta 

 which recoil as from immobile oiistacles — varii'^ in .1 curious manner 



Fig. 8 — Above, the A' a-line of molybdenum; below, the same radiation after scatter- 

 ing at 90° from carbon, aluminium, copper and silver. (P. A. Ross) 



from one of these elements to .mother. Mo^~i ol the (|uanta scat- 

 tered by lithium undergo the alter, ilion in wa\e1eni;th which we have 

 calculated; nearly all of the quanta scatlcreil by lead emerge with 

 the same frequency as the incident quanta. Apparently, the heavier 

 the atoms of a substance are, the less conspicuous does Compton's 

 effect become. Further, the relative intensity of the two rays as- 

 sumes different values for one and the same substance, depending 

 on the direction of scattering. This is illustrated in Fig. 9, the curves 

 of which may be interpreted as graphical representations of photo- 

 graphs like those of the foregoing Figure, the ordinate standing for 

 the density of the image on the photographic plate. (Actually, the 

 ordinate stands for a quantity which is much more nearly propor- 

 tional to the true intensity of the rays — that is, the amount of ioniza- 

 tion which they produce in a dense gas.) These cur\es show, in the 

 first place, that the separation between the two scattered rays has 

 the proper theoretical values at the angle 45°, at i)0°, and at 135°; in 

 the second place, among the quanta scattered at 45°, those that 



