56 On Atomic Arrangement in Compounds. 
specific refraction of benzene that the old view is the correct 
one.’ I presume that Dr. Carnelley was here referring to 
the paper in the Berlin Berichte, vol. xiii. p. 1808 (1880); 
and if this is so, there is little doubt that he has misinterpreted 
Thomsen’s conclusions, as the formula given represents only 
six single linkings. The ‘heat of combustion of benzene, if 
the carbons are linked as in Kekulé’s formula, would amount 
to 846,000 units, whereas if there are nine single linkings in 
the molecule it would be 802,330 units. The experimental 
number obtained by Thomsen was found to be 805,800; hence 
he concludes that the six carbon-atoms in benzene are nine 
times singly linked with each other.”” J quote here from my 
own paper, entitled “ Researches on the Relation between the 
Molecular Structure of Carbon Compounds and their Absorp- 
tion-Spectra,” published in the Journal of the Chemical 
Society for April 1881; and my conclusion was that, “ subject 
to the correciness of this deduction, I consider the following 
conclusion to be established :—No molecular arrangement of 
carbon-atoms causes selective absorption unless each carben is 
itself united to other three-carbon atoms, as in the case of 
benzene.” 
In accordance with this view, benzene could be represented 
by a formula such as the following :— 
which is practically the same as Ladenburg’s prism ; and we 
have yet to learn that this is not in harmony with Bruhl’s 
determination of the refraction equivalent. It may be ob- 
served that I have carefully guarded myself against uncon- 
ditionally accepting this last expression, since there are other 
considerations which tend towards favouring that of Kekulé. 
Single, double, or treble linkings are simply an incomplete 
method of representing the relation of the carbon-atoms to 
each other at some particular phase of their vibrations. Such 
representations are fictitious, since they give us no idea of the 
vibrations which are the cause of all the properties of these 
