File:Relative spectral transmission of the atmosphere (1920) (14771810975).jpg

Identifier: relativespectral1637unse (find matches)
Title: Relative spectral transmission of the atmosphere
Year: 1920 (1920s)
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Publisher: National Bureau of Standards
Contributing Library: NIST Research Library
Digitizing Sponsor: NIST Research Library

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atmosphere throughout the visible spectrum.Certain necessary corrections were applied to the observed values,as will be described later. The use of the distant mirror was re-sorted to for the reason that it minimized the equipment and num-ber of operators. The distance from the mirror to the spectro-photometer was 600 m. The nature of the intervening terrainmay be seen in Fig. 1, an aerial photograph taken by Dr. S. M.Burka. The light source and spectrophotometer are indicatedby 5, the distant mirror by D, and the near mirror by N. Aportion of the path over which the beam passed lay over a ravinewith dense woods and foliage, through which ran a brook. Themore distant part of the path lay over vacant and unimprovedcity lots, and was also nearer the ground. Fig. 2 is an approxi-mate vertical section of the country traversed by the light, show-ing these portions together with approximate height above sealevel. Karrer ; Tyndall) Transmission of the Atmosphere 379 7J,&7yj$ JAOSt/1H0/3H
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A/outas &0&£/rw 380 Scientific Papers of the Bureau of Standards (Voi.16 III. SPECTROPHOTOMETRY APPARATUS The spectrophotometric apparatus in the observing station isshown in Fig. 3. The Brace 1 spectrophotometer A was used withmodifications and accessories as noted below. The collimators3 and 7 were equipped with bilateral slits. With the final arrange-ment, the first of these was not essential. Before the slit of thecomparison field (collimator 7) was a ground glass 8 and a mirror 9.The lens 10 and mirror 11 were also necessary elements in the pathof the comparison beam from the lamp 12. The beam of lightab, impinging upon the distant mirror and returning along cd,was focused by an achromatic lens 6—diameter 6 cm, focal length54 cm—at a point in front of the slit attached to the collimator 3.The limiting slit for this collimator was mounted, together with aground glass 4 and prism 5, upon a small table which could bereadily raised to enable the beam coming directly from

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