1831.] On a Pectdiar Class of Acoustical Figures. 315 



developed by Chladni, are so striking as to be recalled to the 

 minds of those who have seen them by the slightest reference. 

 They indicate the quiescent parts of the plates, and visibly 

 figure out what are called the nodal lines. 



2. Afterwards M. Chladni observed that shavings from the 

 hairs of the exciting violin bow did not proceed to the nodal 

 lines, but were gathered together on those parts of the plate 

 the most violently agitated, i. e. at the centres of oscillation. 

 Thus when a square plate of glass held horizontally was 

 nipped above and below at the centre, and made to vibrate by 

 the application of a violin bow to the middle of one edge, so 

 as to produce the lowest possible sound, sand sprinkled on the 

 plate assumed the form of a diagonal cross; but the light 

 shavings were gathered together at those parts towards the 

 middle of the four portions where the vibrations were most 

 powerful and the excursions of the plate greatest. 



3. Many other substances exhibited the same appearance. 

 Lycopodium, which was used as a light powder by Oersted, 

 produced the effect very well. These motions of lycopodium 

 are entirely distinct from those of the same substance upon 

 plates or rods in which longitudinal vibrations are excited. 



4. In August 1827, M. Savart read a paper to the Royal 

 Academy of Sciences*, in which he deduced certain important 

 conclusions respecting the subdivision of vibrating sonorous 

 bodies from the forms thus assumed by light powders. The 

 arrangement of the sand into lines in Chladni's experiments 

 shows a division of the sounding plate into parts, all of which 

 vibrate isochronously, and produce the same tone. This is 

 the principal mode of division. The fine powder which can 

 rest at the places where the sand rests, and also accumulate at 

 other places, traces a more complicated figure than the sand 

 alone, but which is so connected with the first, that, as M. 

 Savart states, " the first being given, the other may be anti- 

 cipated with certainty ; from which it results that every time 

 a body emits sounds, not only is it the seat of many modes of 

 division which are superposed, but amongst all these modes 

 there are always two which are more distinctly established than 

 all the rest. My object in this memoir is to put this fact beyond 

 a doubt, and to study the laws to which they appear subject." 



* Annales de Chiinie, xxxvi. p. 187. 



