. The Astrophysical journal. d produce as far as possiblea certain effect for a given brand of plates. For purposes of completeness in the application of the fourth-root law for the reduction of thermopile-measures, tests were madeupon plates taken with the 40-inch refractor through color-filter andwith isochromatic plates. Fig. 10 shows the magnitudes of thePleiades on Miiller and Kempfs scale platted against the corre-sponding 6^ of the galvanometer-readings. From other series ofmeasurements covering a variety of times of exposure, the slope of THERMOPILE IN PHOTOGRAPHIC PHOTOMETRY 277 the l
. The Astrophysical journal. d produce as far as possiblea certain effect for a given brand of plates. For purposes of completeness in the application of the fourth-root law for the reduction of thermopile-measures, tests were madeupon plates taken with the 40-inch refractor through color-filter andwith isochromatic plates. Fig. 10 shows the magnitudes of thePleiades on Miiller and Kempfs scale platted against the corre-sponding 6^ of the galvanometer-readings. From other series ofmeasurements covering a variety of times of exposure, the slope of THERMOPILE IN PHOTOGRAPHIC PHOTOMETRY 277 the line appears quite independent of the time of exposure, at leastwithin the range of exposures used. Although considerable unpublished material exists relative tothe magnitude-corrections to the center of the plate for the 40-inchrefractor, and further investigations were made using the thermopilemethod for plate measurement, consistent results have not beenobtained which may be trusted within the degree of precision c 1-4. Magnitudes Fig. 10.—From Plate 015, taken with 40-inch refractor and color-filter at YerkesObservator\-. desired. Owing to rapid and uncertain changes in seeing and thegreat focal length, it has been found practically impossible to use thesimple method employed for the caUbration of the reflector as the stars of the Pleiades platted above cover a con-siderable area on the plate, the residuals indicated are doubtlessattributable to this troublesome and uncertain correction to centerwhich has yet to be apphed. A still further difficulty in the wayof applying this correction is the uncertainty of locating with exact-ness the position of this so-called center. Although a rough 2 7S IIAKLAX TRLE STETS(XN approximation for the position of the optical axis with a givenplate may be obtained from the intersection of the prolonged majoraxis of the elongated stellar images near the edge of the plate, theerrors introduced by the uncertainty in the lo
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
