atories. These were held by Lockyer to be
simply the finer constituents of their predecessors, dissociation having
been effected by the higher temperature ensuing upon increased solar
activity. But Father Cortie's supplementary investigations at
Stonyhurst[658] modified, while they in the main substantiated, the
South Kensington results. They showed that the substitution of unknown
for known lines characterizes disturbed spots, at all stages of the
solar cycle, so that no systematic course of chemical change can be said
to affect the sun as a whole. They showed further[659]--from evidence
independent of that obtained by Young in 1892[660]--the remarkable
conspicuousness in spot-spectra of vanadium lines excessively faint in
the Fraunhofer spectrum. Lockyer's "unknown lines" may probably thus be
accounted for. They represent absorption, not by new, but by scarce
elements, especially, Father Cortie thinks, those with atomic weights of
about 50. The circumstance of their development in solar commotions,
largely to the exclusion of iron, is none the less curious; but it
cannot be explained by any process of dissociation.

The theory has, however, to be considered under still another aspect. It
frequently happens that the contortions or displacements due to motion
are seen to affect a single line belonging to a particular substance,
while the other lines of _that same substance_ remain imperturbable.
Now, how is this most singular fact, which seems at first sight to imply
that a body may be at rest and in motion at one and the same instant, to
be accounted for? It is accounted for, on the present hypothesis, easily
enough, by supposing that the rays thus discrepant in their testimony,
do _not_ belong to one kind of matter, but to several, combined at
ordinary temperatures to form a body in appearance "elementary." Of
these different vapours, one or more may of course be rushing rapidly
towards or from the observer, while the others remain still; and since
the line of sight across the average prominence-region penetrates, at
the sun's edge, a depth of about 300,000 miles,[661] all the
incandescent materials separately occurring along which line are
projected into a single "flame" or "cloud," it will be perceived that
there is ample room for diversities of behaviour.

The alternative mode of escape from the perplexity consists in assuming
that the vapour in motion is rendered luminous under conditions which
reduce its spectru