ARTICLES 585 



It is, of course, very interesting to inquire whether this 

 critical electron energy which is required to excite the charac- 

 teristic radiation of an atom is related to any other known 

 characteristics of the atom. It is found that the velocity of 

 the electron is very nearly 2ire 2 N/h, where e is the charge of the 

 electron and N the atomic number, so that Ne, according to 

 present ideas, is the charge on the atom nucleus. If this is an 

 exact relation, it is a proper jumping-off place for a theory. 

 It would be impossible, having got so far, not to make a pass- 

 ing allusion to the ingenious theory of atomic structure put 

 forward by Bohr : but no discussion of it will be attempted. 



This short account of recent work on the spectra of X-rays 

 will show, it is hoped, what great importance lies in work of 

 this kind. The laws which govern the conversion of X-ray 

 energy into electron energy and of the reverse process must 

 be fundamental so far as radiation is concerned. They are 

 sure to throw light both on the processes of radiation and on 

 the nature of the atoms from which radiation proceeds. 



