RESEARCHES IN STELLAR PHOTOMETRY. 
By John A. Parkhurst. 
INTRODUCTION. 
The problems of stellar photometry are closely connected with many cosmic 
questions, primarily with the light changes of variable stars; but they have an 
equally important bearing on the questions of stellar distribution and evolution. 
It has been said by good authorities that it is of more importance to measure 
the light than the place of a star, and if one considers merely the astonishing 
number of variable stars now being discovered, it will be admitted that the import¬ 
ance of stellar photometry can scarcely be overestimated. The material here 
submitted is the natural outgrowth of the writer’s variable-star work, the plans 
being extended as the instrumental and other facilities were improved. 
The following contribution is offered towards the solution of several pho¬ 
tometric problems, among them being: 
(1) The accurate determination of complete light-curves of twelve variable 
stars of long period, having faint minima. 
(2) The question of the behavior of variable stars during their faint stages 
which can only be observed with the largest apertures. 
(3) The adaptation of the Pickering “equalizing wedge photometer” to the 
determinations of magnitudes. 
(4) The photometric measurement of very faint magnitudes, and their 
relation to estimates founded on the limit of visibility of different apertures of 
telescopes. 
I wish to acknowledge here the efficient assistance rendered in the reductions 
by Miss Kate Bloodgood, also by Mr. F. R. Sullivan of the observatory staff, who 
recorded all the photometric measures made with the 40-inch telescope. 
historical. 
The writer’s variable-star work began at Marengo, Illinois, in May, 1893, with 
visual comparisons by Argelander’s method of a list of long-period variables, 
including at first the circumpolar stars in Professor E. C. Pickering’s pamphlet, 
“ Variable Stars of Long Period," published in 1891; with additions, from time 
to time, of new variables which were not receiving sufficient attention elsewhere. 
By the end of 1899 the number of observations amounted to about 5,000, fur¬ 
nishing data for determining 162 maxima and 116 minima. Provisional results 
were published in the Astronomical Journal, vols. 13 to 21, and in Popular Astron¬ 
omy, vols.> 2 to 8. This work was made possible largely by the kind assistance 
of P. S. Yendell, of Dorchester, Massachusetts, who with great patience gave the 
instructions needed by a beginner and corrected the errors into which one was 
so likely to fall; also of Henry M. Parkhurst, of Brooklyn, New York, who, beside 
