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The Beckman quartz photoelectric spectrophotometer, covering the wave-length range from about 200 to 1200 millimicrons is proving of great utility in spectral transmission and absorption measurements. Essential features of the instrument are described, including a constant-temperature inclosure (for samples) designed and constructed at the Bureau. Various instrumental characteristics are noted and possible errors discussed, particularly those that may be present in the measurement of polarizing samples. Wave-length calibrations are shown for two instruments. A detailed over-all check of the reliability of data obtained on the Beckman spectrophotometer by means of glass standards of spectral transmittance shows it to give results over the wave-length range from 390 to 750 mμ fully as reliable as those obtained with our other spectrophotometers, if various precautions are taken.

Standard light sources A, B, and C were adopted by the International Commission on Illumination (C.I.E.) in 1931 for the colorimetry of materials. Source A is an incandescent lamp operated at 2854°K. Sources B and C, representative of average noon sunlight and average daylight, respectively, are produced by passing radiant flux from source A through specified Davis-Gibson filters described in Bureau of Standards Miscellaneous Publication M114 (1931).The C.I.E. published relative energy data only from 370 to 720 mµ. The present paper gives data for these sources in the ultraviolet and extends the data in the red to 780 mµ. The new data were reported through the U. S. Secretariat Committee to the C.I.E. at its 1951 meeting. The values in the ultraviolet were reported to the Optical Society of America at its March, 1952, meeting.

Standard light sources A, B, and C were adopted by the International Commission on Illumination (C.I.E.) in 1931 for the colorimetry of materials. Source A is an incandescent lamp operated at 2854°K. Sources B and C, representative of average noon sunlight and average daylight, respectively, are produced by passing radiant flux from source A through specified Davis-Gibson filters described in Bureau of Standards Miscellaneous Publication M114 (1931).The C.I.E. published relative energy data only from 370 to 720 mµ. The present paper gives data for these sources in the ultraviolet and extends the data in the red to 780 mµ. The new data were reported through the U. S. Secretariat Committee to the C.I.E. at its 1951 meeting. The values in the ultraviolet were reported to the Optical Society of America at its March, 1952, meeting.

A filter transmitting a narrow band of light at 560 mμ is of particular importance in the colorimetry of sugar solutions, in optical pyrometry, in abridged spectrophotometry, and in photometry. A new 4-component glass filter has been designed which isolates and transmits light at 560 mμ more effectively than previous filters. Two components of this filter are of Corning glass and two of Jena glass. The spectral transmissions of the filter and its components are illustrated. The spectral centroid of the light transmitted by the filter is at 560 mμ for both incandescent and daylight illuminants. Various other luminous characteristics of the filter are also defined and values given.