rays from every portion of his surface indiscriminately. The answer to
the inquiry was prompt and unmistakable, and was again, in this case,
adverse to the French theorist's view. The obscurations in question were
found to be produced by no deficiency of emissive power, but by an
increase of absorptive action. The background of variegated light
remains unchanged, but more of it is stopped by the interposition of a
dense mass of relatively cool vapours. The spectrum of a sun-spot is
crossed by the same set of multitudinous dark lines, with some minor
differences, visible in the ordinary solar spectrum. We must then
conclude that the same vapours (speaking generally) which are dispersed
over the unbroken solar surface are accumulated in the umbral cavity,
the compression incident to such accumulation being betrayed by the
thickening of certain lines of absorption. But there is also a general
absorption, extending almost continuously from one end of the
spot-spectrum to the other. Using, however, a spectroscope of
exceptionally high dispersive power, Professor Young of Princeton, New
Jersey, succeeded in 1883 in "resolving" the supposed continuous
obscurity of spot-spectra into a countless multitude of fine dark lines
set very close together.[462] Their structure was seen still more
perfectly, about five years later, by M. Duner,[463] Director of the
Upsala Observatory, who traced besides some shadowy vestiges of the
crowded doublets and triplets forming the array, from the spots on to
the general solar surface. They cease to be separable in the blue part
of the spectrum; and the ultra-violet radiations of spots show nothing
distinctive.[464]

As to the movements of the constipated vapours forming spots, the
spectroscope is also competent to supply information. The principle of
the method by which it is procured will be explained farther on. Suffice
it here to say that the transport, at any considerable velocity, to or
from the eye of the gaseous material giving bright or dark lines, can be
measured by the displacement of such lines from their previously known
normal positions. In this way movements have been detected in or above
spots of enormous rapidity, ranging up to 320 _miles per second_. But
the result, so far, has been to negative the ascription to them of any
systematic direction. Uprushes and downrushes are doubtless, as Father
Cortie remarks,[465] "correlated phenomena in the production of a
sun-spot"; but neit