Lockyer, Norman, Sir, 1836-1920, Seabroke, G. M. (George Mitchell), 1848-1918 · London, Macmillan and co. · leaf 423
the direct 400 STARGAZING : PAST AND PRESENT. [book vi. vision, whicli is largely used for pocket instruments.The principle of it is that the light passing through it isdispersed but not turned from its course, just the reverseof the achromatic combination of the object-glass ; acrown-glass prism… … Fig. 178.—Direct Vision Prism. the flint-glass is to a great extent neutralized, therefore,in order to make the instrument as powerful as oneof the ordinary construction, a number of flint-glassprisms are combined with crown-glass ones, as shown inFi^. 178. There is another form of direct-vision…
Astronomy · Telescopes
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