. Relative spectral transmission of the atmosphere . ion of the wave front. The flickering was greatest on theclearest nights. XII. RESULTS The most reliable data were those obtained after the distantmirror was mounted on a concrete pier, and for most of these the 396 Scientific Papers of the Bureau of Standards [Vol. 16 range-finder mirror was used. They are in part plotted in , curves 3 to 8, the observations having been made on thenights of May 5 and 8, inclusive, and May 12. Curves 1 and 2are from observations with the silvered optical flat made on April28 and 29. The silver had tarn
. Relative spectral transmission of the atmosphere . ion of the wave front. The flickering was greatest on theclearest nights. XII. RESULTS The most reliable data were those obtained after the distantmirror was mounted on a concrete pier, and for most of these the 396 Scientific Papers of the Bureau of Standards [Vol. 16 range-finder mirror was used. They are in part plotted in , curves 3 to 8, the observations having been made on thenights of May 5 and 8, inclusive, and May 12. Curves 1 and 2are from observations with the silvered optical flat made on April28 and 29. The silver had tarnished considerably, but its reflect-ing power was determined after the run on April 30 (curve 4,Fig. 7). These observations of curve 4 were the first obtainedafter mounting the mirror on the pier. They are considered tobe as reliable as those obtained with the range-finder earlier data obtained before the construction of the pier,and before certain refinements of methods had been adopted, arenot so reliable. Thev will be discussed H20O 460 500 540 580 620 660 700 WAVE LENGTH (meters x io9) Fig. 11.—Relative ira7ismission of atmosphere; generally overcast and high humidity No. 1, Apr. 2S-29; No. 2, Apr. 29-30; No. 3, May 5-6; No. 4, May 6-7; No. 5, May 6-7, second run; No. 6, May 7-8; No. 7, May 12-13; No. 8, May 12-13, second run For the curves shown in Fig. 11, the weather conditions may bedescribed as being generally overcast and characterized by highhumidity. The curves are identical, within experimental errors,for wave lengths less than 540 m/x, and shows that the transmis-sion uniformly decreases with the wave length. From 540 to690 m/x they are all of the same general type, presenting an inter-esting depression in the region of 590 to 640 nnx, with a minimumat about 610 m/x, and a subsequent rise with a maximum near660 m/x. From 660 to 690 m/x there is in all cases a decrease inrelative transmission. In certain instances, notably curves 3,7,and 8, the
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