PROGRESS IN ASTRONOMICAL PHOTOMETRY. 
BY 
John G. Hagen, S. J. 
[Read before the Society March 2, 1901.] 
In this report on astronomical photometry only a few of 
the most remarkable points of progress will be mentioned, 
viz: photometric catalogues, publications of original obser¬ 
vations of variable stars, explanations of physical causes of 
light variations, and charts for variable stars. 
1. Photometric catalogues .—The third volume of the Pots¬ 
dam Durchmusterung (PD.) has been delayed and may not 
appear in print for another year. A very important work is 
the forty-fifth volume of the Annals of Harvard College Ob¬ 
servatory, now ready for distribution, in which the magni- 
m 
tudes of all the stars as bright as 7.5 or brighter from the 
north pole to-—40° declination are given. This volume 
comprises all the observations of the “ Harvard Photometry ” 
and supersedes the earlier volumes on this subject, notably 
volume 14, which has been so useful for the last twenty 
years. 
For the fainter stars standard magnitudes are now being 
measured with the large telescopes of the country (of the 
Lick, Yerkes, Harvard, and Princeton Observatories). Stars 
have been selected for this purpose in various parts of the 
sky, the faintest of which are of magnitude 14 or 15. The 
results will form part II of volume 37 of the same Annals. 
Photometry comprises color as well as brightness. In this 
respect we have in addition to the Potsdam Durchmusterung 
the very important catalogue of the colors of 1,009 stars by 
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