432 Dr. H. Stanley Allen on Optical Rotation, 



are held conjointly by two atoms (fig. 2). According to a 

 suggestion- made by Lewis and adopted by Langmuir, the 

 electrons, which are held in common between two octets or 

 an octet and a stable pair, are drawn together to form pairs, 



Fiar. 2. 



perhaps by the action of magnetic forces. Thus in methane 

 (CH 4 ) the 8 electrons are located in pairs at the 4 corners 

 of a tetrahedron, each hydrogen nucleus being held by one 

 pair. 



On this view, dextro- and lsevo-rotatory forms of a com- 

 pound may be represented, as I have pointed out previously*, 

 by mirror images as in fig. 3. In this diagram the letters 

 N and S may be supposed to indicate the polarity of the 

 exposed face of the ring-electron. 



Fig. 3. 



A suggestion has been made by W. E. Garner t that a 

 large number of optical isomerides may possibly exist amongst 

 organic compounds in consequence of the right-handed or 



* ' Nature,' vol. cv. p. 71 (1920). 



t W. E. Garner, « Nature,' vol. civ. p. 661 (1920) ; vol. cv. p. 171 

 (1920). See also letters from A. E. Oxley, id. vol. cv. pp. 105, 231 



(1920). 



