38o 
INTERNATIONAL ASTRONOMICAL UNION Proc. N. A. S. 
REPORT OF THE COMMITTEE ON STELLAR PARALLAXES 
At the present time determinations of stellar parallax by the trigono- 
metric method form part of the regular work at the following observatories : 
APERTURB 
CHARACTER 
KOCAL LENGTH 
30 inches 
Photographic Refractor 
46 ft. 
Dearborn 
18.5 
Visual Refractor 
28 
26 
Photographic Refractor 
23 
26 
Visual Refractor 
32 
Mount Wilson 
60 
Reflector 
80 
Swarthmore 
24 
Visual Refractor 
36 
Yerkes 
40 
Visual Refractor 
62 
At these seven institutions material sufficient for the determination of 
three hundred parallaxes is obtained each year. The average probable 
error of one determination is under .01". 
Determination of stellar distances by the spectroscopic method are 
being carried out at Mount Wilson with the 60-inch reflector. When 
the 100-inch telescope is in regular operation, a larger part of the time of 
the 60-inch telescope will probably be devoted to obtaining spectrograms 
for this purpose, so that we may expect a rapid increase in our knowledge 
from this source: This committee recommends that other institutions 
be urged to undertake this work, their programs to include a large number 
of objects already observed by the spectroscopic method. Attention is 
called to the fact that existing spectrograms (obtained, for example, in 
radial velocity investigations) could profitably be examined from the point 
of view of absolute magnitudes and stellar distances, at least for the spec- 
tral types Fo to M. 
The paucity of reliable parallaxes determined by the trigonometric 
method has hitherto been a serious obstacle to the effective application 
of the spectroscopic method, since the latter depends principally upon the 
trigonometric results for the determination of relationships between line 
intensities and absolute magnitudes for the various spectral types. The 
war has delayed the publication of much material that will overcome this 
obstacle to a considerable extent, and it is likely that in a few years ample 
material of this kind will be at hand. One of the most important services 
that observers employing the trigonometric method can render at the 
present time is to arrange their programmes with the needs of the spectro- 
scopic method in mind. 
This committee makes the following recommendations in addition to 
those already mentioned: 
1. That observers employing either method should record the reason 
for each star being placed upon their observing lists, in order that their 
results may he properly used in statistical discussions. 
