Tyndall, John, 1820-1893 · London : Longmans, Green · leaf 79
librium. Permitting a slender beam of intense light tofall upon the mirror, the beam is thrown back by reflec-tion. In my hands is held a small looking-glass, whichreceives the reflected beam, and from which it is againreflected to the screen, forming a small luminous discupon the white surface.…
Sound
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