n
of the sun's velocity, apart from assumptions of any kind. M. Homann's
attempt, in 1885,[1535] to extract some provisional information on the
subject from the radial movements of visually determined stars gave a
fair earnest of what might be done with materials of a better quality.
He arrived at a goal for the sun's way shifted eastward to the
constellation Cygnus--a result congruous with the marked tendency of
recently determined apexes to collect in or near Lyra; and the most
probable corresponding velocity seemed to be about nineteen miles a
second, or just that of the earth in its orbit. A more elaborate
investigation of the same kind, based by Professor Campbell in
1900[1536] upon the motions of 280 stars, determined with extreme
precision, suffered in completeness through lack of available data from
the southern hemisphere. The outcome, accordingly, was an apex most
likely correctly placed as regards right ascension, but displaced
southward by some fifteen degrees. The speed of twelve miles a second,
assigned to the solar translation, approximates doubtless very closely
to the truth.

A successful beginning was made in nebular spectrography by Sir William
Huggins, March 7, 1882.[1537] Five lines in all stamped themselves upon
the plate during forty-five minutes of exposure to the rays of the
strange object in Orion. Of these, four were the known visible lines,
and a fifth, high up in the ultra-violet, at wave-length 3,727, has
evidently peculiar relationships, as yet imperfectly apprehended. It is
strong in the spectra of many planetaries; it helped to characterise the
nebular metamorphosis of Nova Aurigae, yet failed to appear in Nova
Persei. Two additional hydrogen lines, making six in all, were
photographed at Tulse Hill, from the Orion nebula, in 1890;[1538] and
Dr. Copeland's detection in 1886[1539] of the yellow ray D_3 gave the
first hint of the presence of helium in this prodigious formation. Nor
are there wanting spectroscopic indications of its physical connection
with the stars visually involved in it. Sir William and Lady Huggins
found a plate exposed February 5, 1888, impressed with four groups of
fine bright lines, originating in the continuous light of two of the
trapezium-stars, but extending some way into the surrounding
nebula.[1540] And Dr. Scheiner[1541] argued a wider relationship from
the common possession, by the nebula and the chief stars in the
constellation Orion, of a blue line, brigh