Lockyer, Norman, Sir, 1836-1920, Seabroke, G. M. (George Mitchell), 1848-1918 · London, Macmillan and co. · leaf 505
I 1 482 STARGAZING : PAST AND PRESENT. [book vi. require to be exposed for eight minutes, and at the lineH, which is further away from the luminous part of thespectrum than G, there the exposure requisite would betwo or three minutes. In order, to obtain a photograph of the average solarspectrum,… … Fig. 217.—Telespectroscope with Camera for obtaining Photographs of the Solar Prominences. beam, however, should be sent through an opera-glassin order to condense it, and thereby to render theexposure as short as possible. Further, if an electric lamp be mounted as shown inFig. 216, observations,…
Astronomy · Telescopes
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