Stars and telescopes; a hand-book of popular astronomy, founded on the 9th ed. of Lynn's Celestial motions (1899)
Todd, David P. (David Peck), 1855-1939, Lynn, William Thynne, 1835-1911. Celestial motions · Boston, Little, Brown and company · leaf 411
is work Professor Picker-ing devised a novel form of double objective which isequally 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 Brashear) Telescopes and Hoitses 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…
Astronomy
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