RECENT ADVANCES IN SCIENCE 29 



limit too seriously the possible number of rings and the chance 

 of their resultant moment being zero (most substances are dia- 

 magnetic) ; while, if their radii are not very different from one 

 another, an altogether chaotic motion would result quite in- 

 consistent with the precise and definite properties which the 

 atom of each element possesses. This means, for stability, 

 coplanar rings — a state of affairs quite inadequate to account 

 for the facts of stereochemistry. 



Further, on Parson's view purely electrostatic forces of 

 attraction and repulsion between the individual electrons and 

 the positive parts of the atom are insufficient to account for 

 valencies. With his electron shaped as a rapidly rotating 

 ring, he can appeal as well to electromagnetic forces with a 

 magnitude comparable under certain circumstances with the 

 electrostatic. Thus, it is simple enough on electrostatic grounds 

 to explain the bond between a hydrogen atom and a chlorine 

 atom in the molecule of hydrochloric acid, but not so easy to 

 explain the bond between the two hydrogen atoms in the 

 hydrogen molecule. This, however, is rendered more easy if 

 the electromagnetic attraction of two similar electronic orbits 

 is brought into consideration. 



By his ring structure hypothesis, Parson gets rid of two 

 difficulties ab initio — the difficulty of stability and that of 

 energy waste by radiation. His hypothesis is frankly designed 

 for this purpose. Its merits must be judged by its subsequent 

 success in dealing with all the other difficulties which have met 

 the other theories and all the problems which have been raised 

 by the multitude of experimental results available. As regards 

 chemical considerations, no one will deny that the introduc- 

 tion of the ring electron furnishes a means of avoiding many 

 serious difficulties which are met when the attempt is made to 

 apply earlier conceptions of the electron to problems of chemi- 

 cal constitution and stereochemistry. In particular, Parson 

 has shown that a group of eight of his ring electrons forms an 

 extremely stable system of low magnetic energy. They have 

 their centres on the corners of a cube, and wide limits of 

 orientation are possible for the rings without upsetting the 

 stability of the group. Now this compact group of eight is 

 just what is required to account for the presence of eight 

 groups in the periodic table, and a considerable portion of 

 Parson's paper is devoted to a close discussion of the periodic 



