. Relative spectral transmission of the atmosphere . 0 600 6H0 680 720 .WAVE LENGTH (MeTeRsxio-»; Fig 7.—Relative reflecting power of mirrors No. 1, range-finder mirror; No. 2, freshly silvered flat; No. 3, slightly tarnished flat; No. 4, very tarnished flat; No. s, two range-finder mirrors nearly as possible identical with those when the distant mirroris used, the near mirror must be sufficiently far away that the 1 ft2« I 80 h^JL M *1 ?l 1 fr 4 r* 1 ? « H H P ^ L4 N j>i u ] 3? Si I H * K 40 u [ ] ] 1 * 00 ^0 460 5<?<? ,*&? ^30 620 e$o WJl/r LENGTtf Qmeters x 10*) Fig. 8.—Te.^ of rel
. Relative spectral transmission of the atmosphere . 0 600 6H0 680 720 .WAVE LENGTH (MeTeRsxio-»; Fig 7.—Relative reflecting power of mirrors No. 1, range-finder mirror; No. 2, freshly silvered flat; No. 3, slightly tarnished flat; No. 4, very tarnished flat; No. s, two range-finder mirrors nearly as possible identical with those when the distant mirroris used, the near mirror must be sufficiently far away that the 1 ft2« I 80 h^JL M *1 ?l 1 fr 4 r* 1 ? « H H P ^ L4 N j>i u ] 3? Si I H * K 40 u [ ] ] 1 * 00 ^0 460 5<?<? ,*&? ^30 620 e$o WJl/r LENGTtf Qmeters x 10*) Fig. 8.—Te.^ of reliability of the method by use of near station Full line: Reflecting power of two range-finder mirrors. Points indicated: Observed relative transmission uncorrected for reflection of mirrors image of the light source formed by the lens 6, Fig. 3, is approxi-mately of the same dimensions as that when the distant mirroris used. The results of this test are represented in Fig. 8, con- Scientific Papers of the Bureau of Standards, Vol. 16. Fig. 6.—An aerial view showing the near mirror station N and the observingstation S, containing spectrophotometer and light source TynZui Transmission of the Atmosphere 385 sisting of seven sets of observations taken on the nights of May13 and 14, 14 and 15, 15 and 16, 19 and 20, 22 and 23, 26 and 27,27 and 28, 1919. The observations corresponding, respectively,to these dates are dots, hooked circles, dashes, triangles, circles,squares, and crosses. The full-line curve taken from Fig. 7 isthat of the relative reflection for the two mirrors used. The dataof May. 15 and 16, represented by dashes, are very scattered onaccount of some mist in the atmosphere that night and somesmoke carried by a north wind from the near-by power set is inserted merely to show the extremely erratic effectsof polluted atmospheres and should not be considered in forminga judgment of the results. There is in all the rest some indicationof absorption and
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