CONTEMPORARY ADVANCES IN PHYSICS 



689 



their observations however to those which had been deflected only a 

 Httle or not at all. They found that many suffered an energy-loss of 

 about 12.6 equivalent volts, evidently the same which Harnwell was 

 later to observe. Arnot used Dymond's method in a study of mercury 

 vapor; he detected energy-losses corresponding to excitation and 

 ionization, and traced curves resembling those of Fig. 11. Rudberg, 

 working with nitrogen, and likewise concerning himself only with 



5 10 15 20 25 30 35 40 45* 



e 



Fig. 11 — Distribution-in-angle of electrons scattered from molecules and atoms of 

 hydrogen. (G. P. Harnwell, Physical Review.) 



electrons which were practically not deflected at all in their collisions, 

 obtained curves with maxima remarkably sharp, indicating several 

 distinct and very precisely determined energy-transfers, the two most 

 prominent amounting to 12.78 and to 9.25 equivalent volts. 



Yet another device is that of R. Kollath, which is much simpler 

 than Harnwell's, but functions only for one small range of angles of 

 scattering; it is shown in Fig. 12. The primary electron-beam passes 

 through the slits Bi and B^, then onward into the collecting-chamber 

 A\ those corpuscles which are scattered at angles between (roughly) 

 87° and 93° are able to pass between the flat metal rings L of which one 



