The Astrophysical journal . rectdefinition of spectral hues. In most of the negatives the Fraun-hofer lines are purposely obliterated, because they interfere with themeasurement. It is, however, now a matter of common knowledgethat good-quality replica-gratings leave little, if anything, to bedesired on the score of definition, and, except for the spectroscopyof position, even those of secondary quality define jar in excess of therequirements of the work in hand. REPLICA GRATING SPECTROGRAPH The form of spectrograph suggested for use with the replica hasbeen modeled along lines somewhat simila
The Astrophysical journal . rectdefinition of spectral hues. In most of the negatives the Fraun-hofer lines are purposely obliterated, because they interfere with themeasurement. It is, however, now a matter of common knowledgethat good-quality replica-gratings leave little, if anything, to bedesired on the score of definition, and, except for the spectroscopyof position, even those of secondary quality define jar in excess of therequirements of the work in hand. REPLICA GRATING SPECTROGRAPH The form of spectrograph suggested for use with the replica hasbeen modeled along lines somewhat similar to an instrument devisedby Baker,1 but possesses several modifications. Its plan may beeasily understood by reference to the drawing (Fig. 4). Simplicitycombined with rigidity was the principal aim in the construction ofthe instrument. Lenses of greater focal length could be used for theformation of a longer spectrum without any difference ensuing save 1 Journal Royal Photograpliic Society, 46, 161, 1906. SENSITOMETRY 123. 124 ROBERT JAMES WALLACE in the length of exposure time, but the dimensions of the instrumentwould thereby be increased. With the specifications given the spec-trum measures cm from X 6900 to X-3550 (B-N), which is ofgood measurable length. For special examination of the red andinfra-red end a narrow brass wedge-frame is inserted at A2, whichchanges the angle of the collimator and brings the C line (X 6563)in the center of the plate. To enter here into a discussion of theresolving power of the instrument is unnecessary when we take intoconsideration the work for which it is intended. The spectrographmay, if furnished with slit and lenses of good quality, be used for avery high grade of spectroscopic work. For visual observation aneyepiece can be held by means of an adapter at the plane of theplate. The spectrograph should occupy a definite permanent position inthe laboratory, with the collimator pointing to the northern skyalways at the same angle. This
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
