The book of stars; being a simple explanation of the stars and their uses to boy life, written to conform to the tests of the Boy scouts (1915)
Collins, A. Frederick (Archie Frederick), 1869- · New York, D. Appleton and company · leaf 153
134 THE BOOK OF THE STARS holding a sheet of paper, or the hand under the lens and lettingthe sunlight pass through it; where the spot of light is smallest … Fig. 145.—Prism Forming a Spectrum. and brightest the distance of this point from the lens is calledthe focal length. A concave lens is a lens which is thinner at the middle than
Astronomy · Stars
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