Sound : a course of eight lectures delivered at the Royal Institution of Great Britain / by John Tyndall.

  • John Tyndall
Date:
1869
Catalogue details

Licence: Public Domain Mark

Credit: Sound : a course of eight lectures delivered at the Royal Institution of Great Britain / by John Tyndall. Source: Wellcome Collection.

    161/400 page 141
    tingen, made me presume that the different vibratory motions of a sonorous plate might also present different appearances, if a little sand or some other similar substance were spread on the surface. On employing this means, the first figure that presented itself to my eyes upon the cir- cular plate already mentioned, resembled a star with ten or twelve rays, and the very acute sound, in the series alluded to, was that which agreed with the square of the number of diametral lines.’ I will now illustrate the experiments of Chladni, commen- cing with a square plate of glass held by a suitable clamp at its centre. The plate might be held with the finger and thumb, if they could only reach far enough. Scattering fine sand over the plate, the middle point of one of its Fig. 61. Fig. 62. Fig. 63. edges is damped by touching it with the finger nail, and a bow is drawn across the edge of the plate, near one of its corners. The sand is tossed away from certain parts of the surface, and collects along two nodal lines which divide the large square into four smaller ones, as in fig. 61. This division of the plate corresponds to its deepest tone. The signs + and — employed in these figures denote that the two squares on which they occur are always moving in opposite directions. When the squares marked + are above the average level of the plate those marked — are below it; and when those marked —are above the average level those marked + are below it. The nodal lines mark the boundaries of these opposing motions.
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