402 



Mr. S. A. Sworn on the Constitution 



(5') In fig. 4 and also in fig. 5, 



IC " sc + / 



where / is the focal length of the lens. 



I am, &c, 



Magnus Maclean. 



Physical Laboratory, The University, 

 Glasgow, October 16, 1889. 



XL VII. The Constitution of the Aromatic Nucleus. By S. A. 

 Sworn, B.A., Assoc. R.C.Sc.L, late Brakenbury Scholar 

 . of Balliol College, Oxford.* 



ONE of the most important developments of theoretical 

 chemistry in recent times has been the view that sym- 

 metry plays an important part in the aggregation of those 

 atoms which, when combined together, form the fundamental 

 molecular units of organic chemistry. Van't Hoff, in the case 

 of the derivatives of marsh-gas, has brought forward views 

 which have received much, and for the most part favourable, 

 criticism. On the other hand the views of R. Meyer {Ber. 

 xv. p. 1823) and of J. Thomsen (Ber. xix. p. 2944), who have 

 each proposed a symmetrical formula for benzene, have been 

 less favourably received. 



It is a remarkable fact that closed chains consisting of six 

 carbon atoms (never five or seven atoms) are produced by 

 the action of dehydrating agents upon such bodies as acetone, 

 and by other condensations. Observations on the specific 

 volumes of aromatic compounds further show that these 

 closed chains are characterized by a compactness of molecular 



* Communicated by the Author. 



