Identifier: com116136561915244244cobl (find matches)
Title: A comparison of stellar radiometers and radiometric measurements on 110 stars
Year: 1915 (1910s)
Authors: Coblentz, W.W.
Subjects: stars
Publisher: National Bureau of Standards
Contributing Library: NIST Research Library
Digitizing Sponsor: NIST Research Library

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Fig. 3.—Stellar thermocouples mounted in an evacuated glass container
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cobientz) Stellar Radiation Measurements 625 3. THE METHOD USED FOR MAINTAINING A VACUUM One of the difficulties with vacuum radiometers is that they cannot be evacuated and sealed permanently, because vapors are givenoff from the walls of the container and from the lampblack-absorbing surfaces. The vapors become disengaged slowly, so thatin time the radiation sensitivity of the radiometer is reduced.Provision must therefore be made to remove these vapors as theybecome disengaged. It is a well-known fact that metallic calcium, when heated, hasthe property of combining with all atmospheric gases exceptargon. The application of this property of metallic calcium asan evacuator has been suggested as a result of the researches madeby Moissan 16 and by Arndt17. Experiments on the productionof high vacua by means of metallic calcium have been made bySoddy 18. A summary of the results of these experiments may befound in Balys Spectroscopy.19 In preparing the receptacles for the thermoelements

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