Stars and telescopes; a hand-book of popular astronomy founded on the 9th ed. of Lynn's Celestial motions (1901)
Todd, David P. (David Peck), 1855-1939, Lynn, William Thynne, 1835-1911 · Boston, Little, Brown · leaf 405
is work Professor Picker-ing devised a novel form of double objective which isequallv efficient for both photographic and opticalwork. This long-sought result is obtained by figuringthe two faces of the crown lens very different in curva-ture, and modifying the cell so that the flint lens maybe… … HALES TYPE OF SPECTRO-HELIOGRAPH (Constructed by BrasHHAR) Telescopes and Houses for Them 353 and separating the flint three inches from it, the com-bination becomes an objective perfectly corrected forthe actinic rays — or nearly so. The fact, however,seems to be that there is a trifling sacrifice…
Astronomy
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