44 
IOWA ACADEMY OF SCIENCE Voi,. XXIX, 1922 
distances of the stars by means of their spectra and apparent 
magnitude, though depending fundamentally on direct measure- 
ments for its scale. Dr. H. H. Turner of the Greenwich observa- 
tory, commenting upon the accordance of the trigonometric par- 
allaxes as measured by Dr. S. A. Mitchell at the Leander McCor- 
mick observatory with the spectroscopic parallaxes as determined 
by Dr. W. S. Adams at Mount Wilson, said : “It gives good as- 
surance that Dr. Adams’ working curves for inferring parallaxes 
which were necessarily formed by a series of approximations 
(trial and error), are approaching final shape, if indeed they have 
not already attained it, and I will venture to add a word of ad- 
miration for the great advance in our knowledge of the distance 
of the stars rendered conspicuous by this most beautiful accordance 
of the two methods.” 
With these methods and the ever-increasing mass of data made 
possible by our modern observatories, we have a system of 
measuring distance beyond the most daring dream of celestial 
mechanics. Dr. H. D. Curtis, director of the Allegheny observa- 
tory has examined about five thousand separate parallax results 
from which he has selected one thousand six hundred strictly 
modern values for one thousand one hundred stars, and plotted 
their absolute magnitude against spectral type, the results of 
which investigation will be shown on the screen. Through his 
extensive study of stellar clusters Dr. Shapley, director' of the 
Harvard College Observatory, has shown remarkable correlations 
between the members of star clusters and like members in the 
solar neighborhood, which has extended our knowledge of the 
star clusters and groups of stars to unbelievable limits. 
For example, in a series of papers entitled “Studies Based 
on the Colors and Magnitudes in Stellar Clusters” he finds that 
a wide range of color is present in star clusters, but that change 
of color with brightness is hardly perceptible, that magnitudes of 
the blue stars seem to indicate the remoteness of the star clusters 
and also that they are of great dimensions. He further deduces 
that cluster stars are very probably giants in luminosity and ac- 
cordingly the distance of the groups must be of the order of 
fifteen thousand light years. The wide dispersion in magnitude 
of both blue and red stars indicates a similarly great distance for 
the neighboring galactic clouds. He suggests that the extent of 
the stellar clouds in the line of sight is relatively very great. In 
fact, the depth may be as great as or greater than the distance of 
the nearer boundary. 
