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Brﬁcke, I may say, also found the particles to be of ultra-
microscopic magnitude.

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, as many of you know,
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 ex-
periment described by M. Morren of Marseilles at the last
meeting of the British Association. Sulphur and oxygen
combine to form sulphurous acid gas. It is this choking
gas that is smelt when a sulphur-match is burnt in air.
Two atoms of oxygen and one of sulphur constitute the
molecule of sulphurous acid. Now it has been recently
shown in a great number of instances that waves of ether
issuing from a strong source, such as the sun or the
electric light, are competent to shake asunder the atoms
of gaseous molecules. A chemist wouldlcall this “ decom-
position” by light; but it behooves us, who are examin-
ing 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 ether-waves. Enclosing the sub-
stance 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 is as empty
as a vacuum. Soon, however, along the track of the
beam ,a beautiful sky-blue color is observed, which is
due to the liberated particles of sulphur. For a time
the blue groWs more intense; it then becomes whitish;

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