The spectra, therefore, always indicating the molecular constitution of
^ises, ought to be more complicated also, than it was thought at first
By these considerations, a new importance, a rather physical one, is
given to spectral analysis. You may recognize by the spectrum of a
gas, not only the chemical nature of the gas, but you may also obtain
mdications of its more intimate molecular structure — quite a new
branch of science. Allow me now to select out of the results already
obtained two instances only. Let me try to give what I may call the
history of the spectra of two elementary bodies — of sulphur and nitro-
gen. In order to analyze by the prism the beautiful light produced
by the electric current, if it pass through a rarefied gas, 1 gave to the
tube in which the gas is included such a form that its middle part was
capillary. Thus I got within this part of the tube a brilliant film of
lignt, extremely fitted to be e2canuned by the prism. After having
provided myself with apparatus more suited to my purposes, I asked,
about a year ago, my friend. Prof. Hittorf, of Munster, to join me in
taking up my former researches. The very first results we obtained
in operating on gases of a greater density opened to us an immense
field of new investigation. We found that the very same elementary
substance may have two, even three, absolutely difierent spectra,
which only depend on temperature. In our experiments we made use
of RuhmkorfTs induction coil, whose discharge was sent through our
spectral tubes. In order to increase at other times the heating power
of the discharge, we made use of a Leyden jar. Now, let us sup^^ a
spectral tube, most highly exhausted by Geisslex^a xaexcxxx^ ^vmi^^ ^^^ti-^



136 ANNUAL OF SCIBKTIFIC DISCOYEBY.
