199 
1879J -* Proceedings of Societies. 
1. The- normal alcohols of the series C n H 2u + I OH are remark- 
able for transparency to the ultra-violet rays of the 
spectrum, pure methylic alcohol being as nearly so as 
water. 
2. The normal fatty acids exhibit a greater absorption of the 
more refrangible rays of the ultra-violet spectrum than 
the normal alcohols containing the same number of carbon 
atoms. 
3. There is an increased absorption of the more refrangible 
rays corresponding to each increment of CH 2 in the mole- 
cule of the alcohols and acids. 
4. Like the alcohols and acids, the ethereal salts derived from 
them are highly transparent to the ultra-violet rays, and 
do not exhibit absorption-bands. 
In order to ascertain whether isomeric bodies exhibited similar 
or identical absorption-spectra, a series of benzene derivatives 
was examined. The results may be summarised as follows : — 
1. Benzene, and the hydrocarbons, the phenols, acids, and 
amines derived therefrom, are remarkable — first, for their 
powerful absorption of the ultra-violet rays ; secondly, for 
the absorption-bands made visible by dissolving them in 
water or alcohol, and diluting ; and thirdly, for the extra* 
ordinary intensity of these absorption-bands, — that is to 
say, their power of resisting dilution. 
2. Isomeric bodies, containing the benzene nucleus, exhibit 
widely different spectra, inasmuch as their absorption-bands 
vary in position and in intensity. 
3. The photographic absorption-spectra can be employed as a 
means of identifying organic substances, and as a most 
delicate test of their purity. The curves obtained by co- 
ordinating the extent of dilution with the position of the 
rays of the spedtrum absorbed by the solution form a 
strongly-marked and often a highly characteristic feature 
of many organic compounds. 
There is a curious feature in connection with the position of 
the absorption-bands ; at the less refrangible end they either 
begin at line 12 Cd or line 17 Cd, and those which begin at 12 
end a little beyond 17. 
“ On the Electromagnetic Theory of the Reflection and Re- 
fraction of Light,” by George Francis Fitzgerald, M.A., Fellow 
of Trinity College, Dublin. The author shows that the mtthod 
adopted in his former paper on Magnetic Reflection, in the 
“ Proceedings of the Royal Society” for 1876 (No. 176), is justi- 
fied, and that it is legitimate to consider an incident plane polar- 
ised ray as composed of two oppositely circularly polarised rays, 
each of which is reflected according to its own laws. He con- 
siders next the cases of the magnetisation being all normal to 
the surface, and all in the surface and the plane of incidence, and 
