CELESTIAL SPECTROSCOPY. 83 
A direct determination of the relative temperature of the photo- 
spheres of the stars might possibly be obtained in some cases from 
the relative position of maximum radiation of their continuous spectra. 
Langley has shown that through the whole range of temperature on 
which we can experiment, and presumably at temperatures beyond, the 
maximum of radiation power in solid bodies gradually shifts upwards 
in the spectrum from the infra-red through the red and orange, and 
that in the sun it has reached the blue. 
The defined character, as a rule, of the stellar lines of absorption 
suggests that the vapors producing them do not at the same time 
exert any strong power of general absorption. Consequently, we 
should probably not go far wrong, when the photosphere consists of 
liquid or solid particles, if we could compare select parts of the con- 
tinuous spectrum between the stronger lines, or where they are fewest. 
It is obvious that, if extended portions of different stellar spectra 
were compared, their true relation would be obscured by the line- 
absorption. 
The increase of temperature, as shown by the rise in the spectrum of 
the maximum of radiation, may not always be accompanied by a cor- 
responding greater brightness of a star as estimated by the eye, which 
isan extremely imperfect photometric instrument. Not only is the eye 
blind to large regions of radiation, but even for the small range of light 
that we can see the visual effect varies enormously with its color. Ac- 
cording to Prof. Langley, the same amount of energy which just enables 
us to perceive light in the crimson at A would in the green produce a 
visual effect 100,000 times greater. In the violet the proportional effect 
would be 1,600, in the blue 62,000, in the yellow 28,000, in the orange 
14,000, and in the red 1,200. Capt. Abney’s recent experiments make the 
sensitiveness of the eye for the green near F to be 750 times greater than 
for thered about C. Itis for this reason, at least in part, that I suggested 
in 1864, and have since shown by direct observation, that the spectrum of 
the nebula in Andromeda, and presumably of similar nebule, is in ap- 
pearance only wanting in the red. 
The stage at which the maximum radiation is in the green, correspond- 
ing to the eye’s greatest sensitiveness, would be that in which it could 
be most favorably measured by eye photometry. As the maximum rose 
into the violet and beyond, the star would increase in visual brightness, 
but not in proportion to the increase of energy radiated by it. 
The brightness of a star would be affected by the nature of the sub- 
Stance by which the light was chiefly emitted. In the laboratory solid 
carbon exhibits the highest emissive power. A stellar stage in which 
radiation comes, to a large extent, from a photosphere of the solid par- 
ticles of this substance would be favorable for great brilliancy. Though 
the stars are built up of matter essentially similar to that of the sun, it 
does not follow that the proportion of the different elements is every- 
where the same, It may be that the substances condensed in the pho- 
