Lockyer, Norman, Sir, 1836-1920, Seabroke, G. M. (George Mitchell), 1848-1918 · London, Macmillan and co. · leaf 401
ntil the shadows are equal; then if the distancesfrom the screen are unequal the lights are unequal, and 378 STARGAZING : PAST AND PRESENT. [hook VI. the intensities vary in the inverse ratio of the squaresof the distnnces. This method is practically carried out in tlie telescopeby reducing the… … Fio. 165.—Eniiifords Photonietev. the available area of the object-glass; we can thus viewa star, and gradually reduce the aperture until the staris just visible, or until it just disappears, the latter limitbeing perhaps the most accurate and most usually used ;the aperture is read off on the…
Astronomy · Telescopes
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