176 
ASTRONOMY: ADAMS AND JOY 
Proc. N. a. S. 
The result of the comparison is to indicate that for normal A -type stars 
the absolute magnitude and parallax can be determined with a precision 
quite comparable with other methods from an accurate observation of 
spectral type and the characteristics of the spectral lines. For the c-stars, 
at least in such cases as a Cygni, this is not the case, but these stars appear 
to show in their spectra the phenomena connected with abnormal intrinsic 
brightness, and like the Cepheid variables of the F-type which they re- 
semble noticeably there is every reason to believe they require a separate 
method of reduction. 
Of the application of these results to individual stars it is possible to 
refer only very briefly but the following results may be of interest. 
TYPE COMP. TT OBS. X 
a Lyrae Als 0.09 0.10 
f 1 Ursae Majoris A2s 0.044 0.045 
Taurus Group (26 stars) AO-F 0.024 0.023 
Praesepe (4 stars) A2- A6 0.011 0.011 
The close relationship of these results to certain observations by other 
investigators is of interest. It was found by Hertzsprung and later con- 
firmed by Kohlschiitter^ that the stars in the Taurus cluster show approxi- 
mately a linear relationship between color index or spectral type and 
absolute magnitude. These results deal in general with the larger spec- 
tral classes and later types and not with the subdivisions of a single type as 
is the case here. 
In a recent investigation of the luminosity of the A -type stars, Lind- 
blad^ found that the intensity of the continuous spectrum in a region be- 
tween X3895 and X3907 was less for the intrinsically fainter stars of this 
type than for the brighter stars. This effect he ascribes to the increased 
intensity of the w4ngs of and the greater width and intensity of some 
of the other lines, especially those of iron and silicon, in this region. In 
other words the spectra of the fainter stars are diffuse as compared with 
those of the brighter stars, a result in agreement to that found in this in- 
vestigation. 
There seems to be little doubt that great intrinsic luminosity is associated 
with sharp and narrow lines in all spectral types and that this is due to the 
low density in the atmospheres of such stars. In stars of various spectral 
types, such as ^ Orionis, a Cygni, the Cepheid variables and a Orionis this 
effect is very marked, and the change in the character of the lines of the 
variable star o Ceti from maximum when they are well-defined to minimum 
when they are diffuse and vague is an excellent illustration of the same 
phenomenon. 
1 Hertzsprung, Astron. Nachr., 209 (115). 
2 Kohlschiitter, 211 (289). 
^Lindblad, Astroph. /., 55 (85). 
