164 
Proceedings of the Royal Society of Edinburgh. [Sess. 
ago.* This line of reasoning has doubtless also occurred to others. 
But even with the best will in the world I have never found anything 
that could be interpreted in the sense of the above theories.f All shifts 
of absorption bands are accompanied by changes of shape and intensity 
which are usually much more important ; for example, cf. a little-known 
paper by G. J. Katzj which is quite the best on the subject. Kundt’s 
law, I feel, has been a false clue, and should be forgotten. 
Recently a considerable amount of work has been done by Jones and 
his colleagues § photographing various absorption spectra. They started 
their work in the belief that the dissolved substance usually formed loose 
compounds or “ solvates ” with the solvent, and that from the absorption 
spectra it would be possible both to adduce evidence in support of this 
view and at the same time assign the different bands to their sources, 
solvates, ions, or whatever these were. The solvate coincides to a con- 
siderable extent with my own view as to the watery atmosphere. I 
cannot help feeling, however, that they would have made more progress 
if they had restricted themselves to a narrower field, and used spectro- 
photometry instead of photography. Photographic results are liable to 
misinterpretation ; e.g ., cf. Jones and Strong, Publications of the Carnegie 
Institution, No. 130, p. 141, and elsewhere, where the gradual shift of an 
absorption band as one salt is transformed into another by replacement 
of the acid radical is said to indicate intermediate compounds. This shift 
is merely apparent, and Merton’s criticism || on the point is fully justified. 
With regard to work done from the side of organic chemistry, I think 
the theory of chromophores, chromogenes, etc., is more a question of 
terminology than any thing else ; also that the chemists have too high an 
opinion of Stark’s theories^ 
The benzene ring has given rise to much speculation owing to its 
seven bands in the ultra-violet, and a connection has been sought between 
these bands and the ways in which the ring can oscillate. For this purpose 
the absorption bands in the infra-red are always ignored. I have had 
rough measurements made on the molecular extinction coefficient of 
* “ Untersuchungen fiber den Einfluss der Temperatur auf die Absorption des Lichtes 
in isotropen Korpern,” Ann. d. Phys. (4), 21, p. 572, 1906. 
t This applies also to Dr Havelock’s theory, Proc. Roy. Soc., A, 86, p. 15, 1911. 
f “ Verschiebung der A.bsorptionsstreifen in verschiedenen Losungsmitteln,” Inaug. 
Diss., Erlangen, 1898, Arch. f. wissensch. Photogr., 1, p. 21, 1899. 
§ Publications of the Carnegie Institution , Washington , Nos. 60, 110, 130, 160. 
|| “The Changes in Certain Absorption Spectra in Different Solvents,” Thos. Kalph 
Merton, Proc. Roy. Soc., A, 87. p. 138, 1912. 
TF Cf. Die Beziehungen zwischen Farbe und Konstitution bei organisclien Verbindungen, 
H. Ley, Leipsic, 1911. 
