. The Astrophysical journal. b is about 5 cm indiameter. These bulbs were selected with very great care in orderto obtain bulbs as free from defects as possible. The pyrometer lamp is so mounted that it may be moved acrossthe field of view by a screw motion. Thus the particular part of thefilament that it is desired to use may be easily brought into thecenter of the field of view. In addition to this the mounting is so AN OPTICAL PYROMETER 297 arranged that all other possible adjustments, such as raising andlowering, turning and tipping the bulb, can be easily obtained. As it is sometimes very
. The Astrophysical journal. b is about 5 cm indiameter. These bulbs were selected with very great care in orderto obtain bulbs as free from defects as possible. The pyrometer lamp is so mounted that it may be moved acrossthe field of view by a screw motion. Thus the particular part of thefilament that it is desired to use may be easily brought into thecenter of the field of view. In addition to this the mounting is so AN OPTICAL PYROMETER 297 arranged that all other possible adjustments, such as raising andlowering, turning and tipping the bulb, can be easily obtained. As it is sometimes very desirable to have the pyrometer filamenthorizontal and at other times vertical, the pyrometer lamp-holderF and the eyepiece telescope were made so as to rotate in the collarG. By this means the pyrometer filament can be set at any has been found very convenient when measuring the tempera-ture of a lamp filament. 0\^ing to the variation from the cosinelaw of emission, it is desirable to have the pyrometer filament. Fig. 2.—Optical Pyrometer parallel to the background filament. In this case it is the bright-ness of the central part of the filament that is measured rather thanthe mean brightness across the filament. This average brightnesshas been shown to be about 3 per cent greater than the normalbrightness. It is sometimes desirable to use two difterent pyrometer lampsin the same optical pyrometer. This is necessary when twodifferent observers have to use the same pyrometer but desire touse difterent pyrometer lamps. It is also desirable to have asecond pyrometer lamp to use occasionally to check the calibrationof the pyrometer lamp that is generally used. To be sure, one ^ Astrophysical Journal, 36, 345, 1912. 2q8 IT. E. FORSYTHE pyrometer lamp can be removed and the other put in its place, buta much more accurate procedure is to have the holder large enoughso that both lamps can be kept \\\ the holder at all times. Theholder for the pyrometer lamps can l)e broug
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
