. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. sounds, the fundamental with some over-tone that will give a beautiful compound figure upon thescreen, some circle or ellipse made up of small undu-lations,, which will vary as the wire is struck in differentplaces. If the wire be made fast at its middle, and theother end of it be plucked, the end with the glass willtake up the vibrations at once — a case of sympatheticvibration. If it is not fastened in the middle there willbe little or no movement when th
. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. sounds, the fundamental with some over-tone that will give a beautiful compound figure upon thescreen, some circle or ellipse made up of small undu-lations,, which will vary as the wire is struck in differentplaces. If the wire be made fast at its middle, and theother end of it be plucked, the end with the glass willtake up the vibrations at once — a case of sympatheticvibration. If it is not fastened in the middle there willbe little or no movement when the lower end is struck.(See Tyndall on Sound, pp. 133, 135.) MELDE S EXPERIMENT. To one prong of a small pocket tuning-fork tie apiece of silk thread, six or eight inches long, and tothe other end tie a pin-hook and hang upon it a smallweight, say a shirt-button. Project this with the large 6o THE ART OF PROJECTING. lens, as represented in Fig. 38. First, with the forkheld as indicated, make it to vibrate. The string willdivide up into segments, all of which can be plainly seenand counted. Second, turn the fork so that it vibrates. Fig. 38. in a horizontal plain. The number of segments willbe doubled. Third, hang another button upon the pin-hook, so that the weight will be doubled. Count thesegments while the fork vibrates, both perpendicularlyand horizontally. In this way some of the laws ofvibrating strings can be demonstrated. Fasten a small piece of wire to one prong of the tun-ing-fork, and when the latter is vibrating draw it quicklyacross a piece of smoked glass. The undulating linewill show well when projected. THE OPEIDOSCOPE. Take a tube, of any kind, that is five or six incheslong and an inch or more in diameter, tie a thin rub-ber membrane or a piece of tissue-paper over one end,and on the middle of the membrane glue a piece oflooking-glass that is not more than the eighth of aninch square. The light from the por^e lumiere falls ACOUSTICS. 61 upon a mirror a, and
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherbosto, bookyear1877
