third type.
Professor Pickering discovered the first example of this class, towards
the close of 1886, in Mira Ceti; further detections were made visually
by Mr. Espin; and the conjunction of bright hydrogen-lines with dusky
bands has been proved by Mrs. Fleming's long experience in studying the
Harvard photographs, to indicate unerringly the subjection of the stars
thus characterised to variations of lustre accomplished in some months.

A third variety of gaseous star is named after MM. Wolf and Rayet, who
discovered, at Paris in 1867,[1399] its three typical representatives,
close together in the constellation Cygnus. Six further specimens were
discovered by Dr. Copeland, five of them in the course of a trip for the
exploration of visual facilities in the Andes in 1883;[1400] and a large
number have been made known through spectral photographs taken in both
hemispheres under Professor Pickering's direction. At the close of the
nineteenth century, over a hundred such objects had been registered,
none brighter than the sixth magnitude, with the single exception of
Gamma Argus, the resplendent continuous spectrum of which, first
examined by Respighi and Lockyer in 1871, is embellished with the yellow
and blue rays distinctive of the type.[1401] Here, then, we have a
stellar globe apparently at the highest point of sunlike incandescence,
sharing the peculiarities of bodies verging towards the nebulous state.
Examined with instruments of adequate power, their spectra are seen to
be highly complex. They include a fairly strong continuous element, a
numerous set of absorption-lines, and a range of emission-lines, more or
less completely represented in different stars. Especially conspicuous
is a broad effluence of azure light, found by Dr. Vogel in 1883,[1402]
and by Sir William and Lady Huggins in 1890,[1403] to be of multiple
structure, and hence to vary in its mode of display. Its suggested
identification with the blue carbon-fluting was disproved at Tulse Hill.
Metallic vapours give no certain sign of their presence in the
atmospheres of these remarkable bodies; but nebulum is stated to shine
in some.[1404] Hydrogen and helium account for a large proportion of
their spectral rays. Thirty-two Wolf-Rayet stars were investigated,
spectroscopically and spectrographically, by Professor Campbell with the
great Lick refractor in 1892-94;[1405] and several disclosed the
singularity, already noticed by him in Gamma Argus, of givin