Carpenter, William Benjamin, 1813-1885, Dallinger, W. H. (William Henry), 1842-1909 · Philadelphia, Blakiston · leaf 282
a T\,th, and atransmitted by Powells drylarge as could be utilised. Butwith aperturas such as these, andthe subsequent introduction ofthe apochromatic system oflenses, much larger cones wererequired. To meet this necessityPowell and Lealand, at the urgentsuggestion of English experts,made first a… … Fig. 200.—Powell and Lealands new low-power condenser. This combination consists of aduplex front with two doublet backs ; it is nearly of the same poweras their dry achromatic condenser, but is of much greater aperture.It lias been brought still more recently to a very high state of per-
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