CELESTIAL SPECTROSCOPY. 85 
depth of hydrogen may be less, and possibly the hydrogen molecules 
may be affected by a larger number of encounters with dissimilar mole- 
cules. In some red stars with dark hydro-carbon bands, the hydrogen 
lines have not been certainly observed; if they are really absent it may 
be because the temperature has fallen below the point at which hydrogen 
can exert its characteristic absorption; besides, some hydrogen will 
have united with the carbon. The coming in of the hydro-carbon bands 
may indicate a later evolutional stage, but the temperature may still 
be high, as acetylene can exist in the electric are. 
A number of small stars more or less similar to those which are 
known by the names of their discoverers, Wolf and Rayet, have been 
found by Pickering in his photographs. These are remarkable for sev- 
eral brilliant groups of bright lines, including frequently the hydrogen 
lines and the line D;, upon a continuous spectrum strong in blue and 
violet rays, in which are also dark lines of absorption. As some of the 
bright groups appear in his photographs to agree in position with cor- 
responding bright lines in the planetary nebule, Pickering suggests 
that these stars should be placed in one class with them, but the bright- 
est nebular line is absent from these stars. The simplest conception of 
their nature would be that each star is surrounded by a nebula, the 
bright groups being due to the gaseous matter outside the star. Mr. 
Roberts however has not heen able to bring out any indication of 
nebulosity by prolonged exposure. The remarkable star 7 Argiis may 
belong to this class of the heavenly bodies. 
Gaseous Nebule.—M the nebule the elder Herschel saw portions of 
the fiery mist or “ shining fluid ” out of which the heavens and the earth 
had been slowly fashioned. For a time this view of the nebule gave 
place to that which regarded them as external galaxies, cosmical “ sand 
heaps,” too remote to be resolved into separate stars; though indeed, in 
1858, Mr. Herbert Spencer showed that the observations of nebulze up 
to that time were really in favor of an evolutional progress. 
In 1864, I brought the spectroscope to bear upon them; the bright 
lines which flashed upon the eye showed the source of the light to be 
glowing gas, and so restored these bodies to what is probably their 
true place, as an early stage of sidereal life. 
At that early time our knowledge of stellar spectra was small. For 
this reason partly, and probably also under the undue influence of the- 
ological opinions then widely prevalent, I unwisely wrote in my orig- 
inal paper in 1864, ‘“‘ that in these objects we no longer have to do with 
a special modification of our own type of sun, but find ourselves in 
presence of objects possessing a distinct and peculiar plan of structure.” 
Two years later, however, in a lecture before this Association, I took a 
truer position. ‘Our views of the universe,” I said, ‘“ are undergoing 
important changes; let us wait for more facts, with minds unfettered 
by any dogmatic theory, and therefore free to receive the teaching, 
whatever it may be, of new observations.” 
