1885.] 



Note on an Experiment hy Chladni. 



247 



April 16, 1885. 



THE TREASURER in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Papers were read : — 



L "Note on an Experiment by Chladni." By CHARLES Tom- 

 lixson, F.R.S. Received March 14, 1885. 



[Plate 1.] 



Lord Rayleigh, in a memoir " On the Circulation of Air in Kundt's 

 Tubes." &c, remarks ("Proc.Roy.Soc," xxxvi, 10, and "Phil. Trans.," 

 1884, Part I, p. 1) that "it was discovered by Savart that very 

 fine powder does not collect itself at the nodal lines, as does sand in 

 the production of Chladni's figures, but gathers itself into a cloud, 

 which, after hovering for a time, settles itself over the places of 

 maximum vibration." 



In Savart's memoir, " Sur les Vibrations Nbrmales" ("An. de Ch. 

 et de Ph." for 1827, xxxvi, 187), the author distinctly claims the 

 above-named discovery. At p. 190 he refers to the nodal lines of 

 Chladni, but adds that by mixing with the sand a finer dust, such as 

 lycopodium, " la poussiere fine se reunit pour tracer d'autres lignes 

 circulaires que ce physicien n'a pas connues," &c. 



Faraday, in his critical examination of Savart's memoir (" Phil. 

 Trans.," 1831, p. 299), apparently takes it for granted that Savart 

 started with an original observation. 



But this interesting discovery, which has been so fruitful in beauti- 

 ful results, is really due to Chladni. In his " Traite d'Acoustique," 

 Paris, 1809, he remarks, p. 125: " Si un pen de poussiere fine est 

 melee au sable, elle pourra mieux servir pour faire voir aussi les 

 centres des vibrations, c'est-a-dire, les endroits ou. les parties vibrantes 

 font les plus gran des excursions : les molecules les plus petites de la 

 poussiere s'accumuleront sur ces endroits." 



Chladni is even more explicit in his "Neue Beytrage zur Akustic," 

 (4to, Leipzig, 1817). At p. 7 he recommends " etwas Pulvis lyco- 

 jpodii" as the fine dust to be mixed with the sand; and at p. 69, he 

 remarks that when fine dust accumulates on the centres of vibration, 

 it is in heaps more or less round or long, &c, according to the form 

 assumed by the vibrating part. 



VOL. XXXVIII. ' T 



