Experimental science. Elementary, practical and experimental physics (1890)
Hopkins, George M. (George Milton), 1842-1902 · New York, Munn & co. · leaf 188
h rings of large wire, soldered to-gether so as to form a single wide ring with two circumfer-ential grooves. In the central part of the ring, at the bot-tom, is inserted a standard, and in the top is inserted a shortmetal tube. Over the edges of the ring are stretched disksof the thinnest elastic… … Sound Lens. gas, it may be focused as desired. A watch placed at thefocus upon one side of the lens can be distinctly heard at thefocal point on the opposite side of the lens, when it can beheard only faintly or not at all at points Fig. i6S. only slightly removed from the focus, thusshowing that…
Physics · Lantern projection · Electric apparatus and appliances
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