The Beekman quartz photoeleetri c sp ectroph otcmeter , covering th e wavelength ra nge from a bout 200 to 1,200 m illi microns, is proving of great utility in swctral t ransm ission and absorption m e asurem en ts. Esse n! ia l features of the instrument are described, including a constant-temperature enc losu re (for samples) designed a nd con structed at the Bureau. Varioll s instrumental characteri stics a re noted an d possible errors di scllssed , particularl y those that may be p re ent in the m eas urement of p olarizi ng samp les. Wavelength calibrations a re shown for two i nstruments. A de tailed ove r-all chec k of t he re li ability of data obtai ned on t he Beckman spect rop hotome ter by m eans of g las stand a rds of spectral transmittance shows it to giv e res ults ove r th e wavele ngth r a nge from 390 to 750 millimicrons fu ll y as reli able a s those obtain ed with othe r spectrophotom et ers, if indi cated precauti ons are taken.
This paper is a continuation of Bureau Research Paper RP1209 and describes the cooperative work done by the Association of American Railroads Signal Section, Corning Glass Works, and the National Bureau of Standards leading to the formulation of the AAR Signal Section specifications for signal colors and glasses. Red.-Will be of such quality that all yellow rays of light are absorbed, the spectrum being either red, or red and orange. The photometric value shall be, light 125, standard 100, dark 75. Green.-Will be of the color known as admiralty green, having a slightly bluish tint. The spectrum shall show very little yellow, being a full green with some blue. The photometric value shall be, light 125, standard 100, dark 75. Yellow.-Will give a spectrum showing a full yellow band, most of the red and slightly of the green. The photometric value shall be, Jight 120, standard 100, dark 80. Blue.-Will give a spectrum having a full blue band, with a narrow band of green. The photometric value shall be, light 125, standard 100, dark 75. Purple.-Will give a spectrum showing a considerable proportion of both red and blue. The photometric value shall be, li ght 125, standard 100, dark 75. Lunar White.-Shall show a maximum of absorption for the yellow. The photometric value shall be, light 120, standard 100, dark 80.
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