. The Astrophysical journal. so term the apparatus, has been shown to be a function of rfor any particular diaphragm, it becomes important to investigatethe changing effect of error in 6 upon the resulting magnitude. Making use of the equation of reduction (4), and difTerentiating, we obtain dm_ (3 If the galvanometer-deflections are recorded in centimeters, thevalue of 13 for the Dearborn plates is very nearly The sameis true for Cramer plates and color-filter used with the 6-inch Zeissdoublet of the Yerkes Observatory. If we assume for the error ofthe mean of several settings on a star
. The Astrophysical journal. so term the apparatus, has been shown to be a function of rfor any particular diaphragm, it becomes important to investigatethe changing effect of error in 6 upon the resulting magnitude. Making use of the equation of reduction (4), and difTerentiating, we obtain dm_ (3 If the galvanometer-deflections are recorded in centimeters, thevalue of 13 for the Dearborn plates is very nearly The sameis true for Cramer plates and color-filter used with the 6-inch Zeissdoublet of the Yerkes Observatory. If we assume for the error ofthe mean of several settings on a star an accidental error not THERMOPILE IN PHOTOGRAPHIC PHOTOMETRY 269 greater than A5 = cm, a very plausible assumption, we mayexpress the resulting error in stellar magnitudes as . ^ ,_3 ^1^1 = —^1—= *.40* A was therefore to be platted for j3 = using values of 5 asabscissae and the corresponding computed value of Am as ordinates(Fig. 6). Similarly, a family of such curves could be constructed. 40 60 Gah anometer 5 in mm Fig. 6.—Precision curve for /3 = 80 with the parameter /3. Such a curve serves at once to indicate thedegree of precision attainable with given conditions of plate,galvanometer, and diaphragm. As will be seen, for example, when^, the fall in galvanometer-deflection due to the interposition of thestellar image, is equal to i cm, the error in magnitude resulting froma reading-error of cm, will be o^oi6 and will remain less thano^^oi if 5 does not fall under cm. Unfortunately, systematic 270 HARLAN TRUE STETSON errors due to conditions of atmospheric transparency or irregu-larities in seeing and plate-sensitiveness seldom warrant higherprecision in measurement, though such should be easily obtainableif the stellar images are not too minute to afford larger values of in the case of the faintest images, readings are seldom madewhen 5<i cm. When, therefore, in a series of measurements dreaches the limiting va
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
