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XVII. On a peculiar class of Acoustical Figures ; and on certain Forms assumed 
by groups of particles upon vibrating elastic Surfaces. By M. Faraday, 
F.R.S. Corr. Mem. Royal Acad. Sciences of Paris, 8$c. 8$c. 
Read May 12, 1831. 
i. The beautiful series of forms assumed by sand, filings, or other grains, 
when lying upon vibrating plates, discovered and 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 ex- 
citing 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 excur- 
sions 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 sub- 
stance 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 
* Annales de Chimie, xxxvi. p. 187. 
