XXV. On the figures obtained by strewing sand on vibrating surfaces, commonly called acoustic figures

Half a century has nearly elapsed since the attention of philosophers was first called to the curious phenomena exhibited when sand is strewed on vi­brating surfaces. Long before this time, Galileo had noticed that small pieces of bristle laid on the sounding-board of a musical instrument, were vio­lently agitated on some parts of the surface, whilst on other parts they did not appear to move; and our own countryman Dr. Hooke, whose sagacity in anti­cipating many of the discoveries of later times has been so frequently remarked, had proposed to observe the vibrations of a bell by strewing flour upon it. But to Chladni is due the sole merit of having discovered the symmetrical figures exhibited on plates of regular forms when caused to sound. His first investi­gations on this subject, Entdeckungen über die Theorie des Klanges, were published in 1787; this work was followed by his Akustik in 1802, and his Neue Beyträge zur Akustik, 1817. A French translation, by himself, of his second work was published at Paris in 1809. All the figures obtained by Chladni on square surfaces are delineated in pages 611, 613, 615; they are copied from the Neue Beyträge, which work contains his most mature experiments; but not having been translated either into French or English, it is but little known in this country. The following are the general results deduced by Chladni from his observations respecting these figures: his works may be referred to for the details omitted, and for those concerning the vibrations of plates in general.