Lectures on light, delivered in the United States in 1872-'73; with an appendix (1873)
Tyndall, John, 1820-1893 · New York, Appleton · leaf 56
the fork by a violin-bow con- OPTICAL EXPRESSION OF SOUND-BEATS. 51 verts that disk into a hand of liglit, and if you simplymove your heads to and fro you cause the image ofthe band to sweep over the retina, drawing it out toa sinuous line, thus proving the periodic character ofthe motion which… … Instead of receiving the beam reflected from thefork on a piece of looking-glass, we now receive it upona second mirror attached to a second fork, and cast byit upon the screen. Both forks now act in combinationupon the beam. The disk is drawn out, as before, theband of light gradually shortening…
Optics
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