Tyndall, John, 1820-1893 · New York : Appleton · leaf 179
ring fine sand over the plate, the middle point ofone of its edges is damped by touching it with the finger-nail, and a bow is drawn across the edge of the plate, nearone of its corners. The sand is tossed away from certainparts of the surface, and collects along two nodal lineswhich divide the… … that the two squares on which they occur are always mov-ing in opposite directions. When the squares marked -f-are above the average level of the plate those marked —are below it; and when those marked — are above theaverage level those marked + are below it. The nodallines mark the boundaries of…
Sound
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