1866. | in a Star in Oorona Borealis. 381 
spectrum. That this is not produced by the faint nebulosity seen 
about the star is evident by the brightness of the lines, and the 
circumstance that they do not extend in the istrument beyond the 
boundaries of the continuous spectrum. The gaseous mass, from 
which this light emanates, must be at a much higher temperature 
than the photosphere of the star, otherwise it would appear impos- 
sible to explain the great brilliancy of the lmes compared with the 
corresponding parts of the continuous spectrum of the photosphere. 
The position of two of the bright lines suggests that this gas may 
consist chiefly of hydrogen. 
If, however, hydrogen be really the source of some of the 
bright lines, the conditions under which the gas emits the light 
must be different from those to which it has been submitted in 
terrestrial observations; for it is well known that the line of 
hydrogen in the green is fainter and more expanded than the 
brilliant red Ime which characterizes the spectrum of this gas. On 
the other hand, the strong absorption indicated by the line F of the 
solar spectrum, and the still stronger corresponding lines in some 
stars, would indicate that under suitable conditions hydrogen may 
emit a strong luminous radiation of this refrangibility. 
When the information received from spectrum analysis is con- 
sidered in connection with the sudden outburst of light in the star, 
and its rapid decline in brightness from between the second and 
third magnitude down to the eighth magnitude in about twelve 
days, the bold speculation presents itself that the star has become 
suddenly enveloped in flames. In consequence of some great con- 
vulsion, on the precise nature of which it would be idle to speculate, 
enormous quantities of gas have been set free. A principal part of 
this gas consists of hydrogen, and this is burning about the star by 
combination with some other element. This flaming gas emits the 
light represented by the spectrum of bright lines. The spectrum 
of the other part of the star’s ight shows that this fierce gaseous 
conflagration has heated to vivid incandescence the solid matter of 
the photosphere. The writer regrets much that he had not the 
opportunity of examining the spectrum of the light of this star at 
an earlier period. It would be of importance to know whether, at 
the first outburst, the bright lines of the gas only would liave been 
seen. Some little time would appear to be necessary for the photo- 
sphere to acquire the temperature necessary for incandescence. 
As the free hydrogen becomes exhausted, the flames abate, the 
incandescence of the photosphere becomes less vivid, and the star 
rapidly wanes. 
We must not forget that light, though a messenger swift of 
wing, requires time to traverse celestial space. The great physical 
convulsion, of which we have been the spectators, is already a 
