continuous spectrum derived from it proved it to be a white-hot solid or
liquid. Herschel and Secchi[439] indicated a cloud-like structure as
that which would best harmonise the whole of the evidence at command.
The novelty introduced by Faye consisted in regarding the photosphere no
longer "as a defined surface, in the mathematical sense, but as a limit
to which, in the general fluid mass, ascending currents carry the
physical or chemical phenomena of incandescence."[440] Uprushing floods
of mixed vapours with strong affinities--say of calcium or sodium and
oxygen--at last attain a region cool enough to permit their combination;
a fine dust of solid or liquid compound particles (of lime or soda, for
example) there collects into the photospheric clouds, and descending by
its own weight in torrents of incandescent rain, is dissociated by the
fierce heat below, and replaced by ascending and combining currents of
similar constitution.

This first attempt to assign the part played in cosmical physics by
chemical affinities was marked by the importation into the theory of the
sun of the now familiar phrase _dissociation_. It is indeed tolerably
certain that no such combinations as those contemplated by Faye occur at
the photospheric level, since the temperature there must be enormously
higher than would be needed to reduce all metallic earths and oxides;
but molecular changes of some kind, dependent perhaps in part upon
electrical conditions, in part upon the effects of radiation into space,
most likely replace them. The conjecture was emitted by Dr. Johnstone
Stoney in 1867[441] that the photospheric clouds are composed of
carbon-particles precipitated from their mounting vapour just where the
temperature is lowered by expansion and radiation to the boiling-point
of that substance. But this view, though countenanced by Angstrom,[442]
and advocated by Hastings of Baltimore,[443] and other authorities,[444]
is open to grave objections.[445]

In Faye's theory, sun-spots were regarded as simply breaks in the
photospheric clouds, where the rising currents had strength to tear them
asunder. It followed that they were regions of increased heat--regions,
in fact, where the temperature was too high to permit the occurrence of
the precipitations to which the photosphere is due. Their obscurity was
attributed, as in Dr. Brester's more recent _Theorie du Soleil_, to
deficiency of emissive power. Yet here the verdict of the spectroscope