ed beam to the
filtrate renders this at once evident.]

But we have it in our power to imitate, far more closely than we have
hitherto done, the natural conditions of this problem. We can
generate, in air, artificial skies, and prove their perfect identity
with the natural one, as regards the exhibition of a number of wholly
unexpected phenomena. By a continuous process of growth, moreover, we
are able to connect sky-matter, if I may use the term, with molecular
matter on the one side, and with molar matter, or matter in sensible
masses, on the other. In illustration of this, I will take an
experiment suggested by some of my own researches, and described by M.
Morren of Marseilles at the Exeter meeting of the British Association.
Sulphur and oxygen combine to form sulphurous acid gas, two atoms of
oxygen and one of sulphur constituting the molecule of sulphurous
acid. It has been recently shown that waves of aether issuing from a
strong source, such as the sun or the electric light, are competent to
shake asunder the atoms of gaseous molecules. [Footnote: See 'New
Chemical Reactions produced by Light,' vol. i.] A chemist would
call this, 'decomposition' by light; but it behoves us, who are
examining the power and function of the imagination, to keep
constantly before us the physical images which underlie our terms.
Therefore I say, sharply and definitely, that the components of the
molecules of sulphurous acid are shaken asunder by the aether-waves.
Enclosing sulphurous acid in a suitable vessel, placing it in a dark
room, and sending through it a powerful beam of light, we at first see
nothing: the vessel containing the gas seems as empty as a vacuum.
Soon, however, along the track of the beam a beautiful sky-blue colour
is observed, which is due to light scattered by the liberated
particles of sulphur. For a time the blue grows more intense; it then
becomes whitish; and ends in a more or less perfect white. When the
action is continued long enough, the tube is filled with a dense cloud
of sulphur particles, which by the application of proper means may be
rendered individually visible. [Footnote: M. Morren was mistaken in
supposing that a modicum of sulphurous acid, in the drying tubes, had
any share in the production of the 'actinic clouds' described by me. A
beautiful case of molecular instability in the presence of light is
furnished by peroxide of chlorine as proved by Professor Dewar. 1878.]

Here, then,