432 FRAGMENTS OF SCIENCE. 
to keep constantly before us the physical images which 
underlie our terms. Therefore I say, sharply and defi- 
nitely, that the components of the molecules of sulphurous 
acid are shaken asunder by the ether-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 color 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.* 
Here, then, our ether-waves untie the bond of chemical 
affinity, and liberate a body sulphur which at ordinary 
temperatures is a solid, and which therefore soon becomes 
an object of the senses. We have first of all the free atoms 
of sulphur, which are incompetent to stir the retina 
sensibly with scattered light. But these atoms gradually 
coalesce and form particles, which grow larger by continual 
accretion, until after a minute or two they appear as sky- 
matter. In this condition they are individually invisible; 
but collectively they send an amount of wave-motion to the 
retina, sufficient to produce the firmamental blue. The 
particles continue, or may be caused to continue, in this 
condition for a considerable time, during which no micro- 
scope can cope with them. But they grow slowly larger, 
and pass by insensible gradations into the state of cloud, 
when they can no longer elude the armed eye. Thus, 
without solution of continuity, we start with matter in the 
atom, and end with matter in the mass; sky-matter being 
the middle term of the series of transformations. 
Instead of sulphurous acid, we might choose a dozen 
other substances, and produce the same effect with all of 
them. In the case of some probably in the case of all it 
is possible to preserve matter in the firmamental condition 
* M. Morren was mistaken in supposing that a modicum of sulphur- 
ous acid, in the drying tubes, bad any share in the production of the 
" actinic clouds " described by me. A beautiful case of molecular 
instability in tbe presence of light is furnished by peroxide of 
chlorine as proved by Professor Dewar. 1878, 
