ceptibility
to adverse atmospheric influences, as to rouse unfounded suspicions of
its variability. The detection of this evasive object gave a hint,
barely intelligible at the time, of further revelations of the same kind
by more cogent means.

A splendid photograph of 1,421 stars in the Pleiades, taken by the MM.
Henry with three hours' exposure, November 16, 1885, showed one of the
brightest of them to have a small spiral nebula, somewhat resembling a
strongly-curved comet's tail, attached to it. The reappearance of this
strange appurtenance on three subsequent plates left no doubt of its
real existence, visually attested at Pulkowa, February 5, 1886, by one
of the first observations made with the 30-inch equatoreal.[1559] Much
smaller apertures, however, sufficed to disclose the "Maia nebula,"
_once it was known to be there_. Not only did it appear greatly extended
in the Vienna 27-inch,[1560] but MM. Perrotin and Thollon saw it with
the Nice 15-inch, and M. Kammermann of Geneva, employing special
precautions, with a refractor of only ten inches aperture.[1561] The
advantage derived by him for bringing it into view, from the insertion
into the eye-piece of a uranium film, gives, with its photographic
intensity, valid proof that a large proportion of the light of this
remarkable object is of the ultra-violet kind.

The beginning thus made was quickly followed up. A picture of the
Pleiades procured at Maghull in eighty-nine minutes, October 23, 1886,
revealed nebulous surroundings to no less than four leading stars of the
group, namely, Alcyone, Electra, Merope, and Maia; and a second
impression, taken in three hours on the following night, showed further
"that the nebulosity extends in streamers and fleecy masses till it
seems almost to fill the spaces between the stars, and to extend far
beyond them."[1562] The coherence of the entire mixed structure was,
moreover, placed beyond doubt by the visibly close relationship of the
stars to the nebulous formations surrounding them in Dr. Roberts's
striking pictures. Thus Goldschmidt's notion that all the clustered
Pleiades constitute, as it were, a second Orion trapezium in the midst
of a huge formation of which Tempel's nebula is but a fragment,[1563]
has been to some extent verified. Yet it seemed fantastic enough in
1863.

Then in 1888 the MM. Henry gave exposures of four hours each to several
plates, which exhibited on development some new features of the
entangled