File:Smithsonian miscellaneous collections (1947) (14765299264).jpg

Identifier: smithsonianmisce1041947smit (find matches)
Title: Smithsonian miscellaneous collections
Year: 1862 (1860s)
Authors: Smithsonian Institution
Subjects: Science
Publisher: Washington : Smithsonian Institution
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Smithsonian Libraries

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Fig. 1. -Cemented combination prism. 6o° Jena U.V. Crown 3199;22° Bausch & Lomb L.F.-3. prism is nearly twice as efficient as the grating. It is suitable formaking continuous energy curves over nearly the whole availablerange of wave lengths that are most interesting with respect to thestars. In the constant-temperature room of the 100-inch telescope onMount Wilson the Coude spectroscope is in frequent use. In ordernot to interfere with it, I use a removable fused-quartz lens of 2.\-inches diameter, having from no- to 120-centimeter focus for thevarious wave lengths. Just beyond the lens is to be the removableprism, of fixed angle of incidence. Just beyond the prism an alumin-ized plane mirror, rotatable by an accurate screw motion, will reflectthe collimated beam vertically downward about 20 feet upon a fused-quartz lens of 31- to 33-centimeters focus, which will form the 4 Astrophys. Journ., vol. 11, p. 135, 1900. SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I04 o.^
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NO. 22 ENERGY SPECTRA OF STARS—ABBOT 5 spectrum within the radiometer. This quartz lens may he tippedbetween stops to throw the spectrum from one vane to the other ofthe radiometer, when visual readings are being made. Radiometer.—I have preferred the radiometer to the bolometer orthe thermopile because it is so simple, does not require a highly sen-sitive galvanometer, is easily shielded from temperature, electrostatic,and magnetic disturbances, may be mounted to be very free frommechanical jars, and finally can reach, both apparently and really,a higher sensibility than either the bolometer or thermopile. If theinstrument is mounted so as to do away with electrostatic influences,its one remaining enemy is the Brownian movements which occur ingases. It is not necessary to tell of the work which has led to the form ofradiometer I now use; I will simply describe it briefly. The suspen-sion, weighing altogether 0.8 milligram, and having a moment ofinertia 5 of about 150X io~9 gr. cm

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