Memoirs . eplaced by a movable diaphragm carryingfive apertures, , , , and mm. in choosing the most suitable aperture and combining with it aslight movement of the ground glass, it was possible to give thedisk of the artificial star any required size and sharpness, to suitthe various telescopes used, and the different atmospheric condi-tions. The use of this instrument is very simple and image of the star to be measured (shown at if in the drawing)is brought between the two images of the artificial star and the wedgeis moved by the pinion R till
Memoirs . eplaced by a movable diaphragm carryingfive apertures, , , , and mm. in choosing the most suitable aperture and combining with it aslight movement of the ground glass, it was possible to give thedisk of the artificial star any required size and sharpness, to suitthe various telescopes used, and the different atmospheric condi-tions. The use of this instrument is very simple and image of the star to be measured (shown at if in the drawing)is brought between the two images of the artificial star and the wedgeis moved by the pinion R till the light of the real star is matched byE, the image formed by reflection from the first surface of the plate B. The position of thewedge is then readonascale divided to twen-ty-fifths of an inch,tenths of a division be-ing estimated. If nowthe light of a star ofknown magnitude bemeasured, the onlyunknown quantity isthe absorption of thewedge expressed in It - in thtiThe Rumfoud Photometer,. MEASURES OF FAINT STANDARD STARS. 231 Measures at Yerkes Observatory. The forty-inch refractor was used by Professor J. A. Parkhurst to measure the mag-nitudes of the stars of sixteenth magnitude, comparing them by means of the Rumfordphotometer with the standard stars of twelfth magnitude. The five faint standards inthe twenty-four Rumford regions north of the celestial equator were selected by Parkhurst. In each case three photometric settings constituted a measure. Each of the fivefaint stars was measured twice, or frequently three times, and each of the five brightstandard stars of twelfth magnitude was measured once, or occasionally twice. Eachregion was measured on at least three nights. Since the calibration of the wedge is fundamental for photometer measures it wasthoroughly investigated by Parkhurst in no less than five different ways so as to eliminateany systematic errors which might be present in a single method of calibration. Three ofthe methods depend on compa
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Keywords: ., bookauthoramer, booksubjectarts, booksubjectscience, bookyear1783
