Tyndall, John, 1820-1893 · London : Longmans, Green · leaf 36
sible. When a candle is placed at this lower focus,you see its image on the gallery above, and I have only toturn the mirror on its stand to make the image of the flamefall upon any one of the row of persons who occupy thefront seat in the gallery. Eemoving the candle, andputting the watch, w, fig.… … One of these two parabolic mirrors, n 7i, fig. 9, is placedupon the table, the other, ni m, being drawn up to aheight of five-and-twenty feet. When the electric lightis placed in the focus a of the lower mirror, a parallel beamrises like a luminous pillar to the upper mirror, whichbrings the beam…
Sound
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