A London encyclopaedia, or universal dictionary of science, art, literature and practical mechanics : comprising a popular view of the present state of knowledge : illustrated by numerous engravings, a general atlas, and appropriate diagrams (1829)
Curtis, Thomas, fl. 1820 · London : Thomas Tegg · leaf 269
393. Parallel rays passing through a doubleconcave lens may also be made to diverge. Thus … the rays a, h, c, &c.,after passing through the doubleconcave lens A, will go on in a diverging state, thesame as if the lens were taken away and the rayshad proceeded from a radiant point F in thevirtual focus or centre of concavity of the lens. 394. The manner in which the foci of lensesof…
Encyclopedias and dictionaries · Aeronautics
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