316 On a Peculiar Class of Acoustical Figures. [1831. 



5. M. Savart then proceeds to establish a secondary mode 

 of division in circular, rectangular, triangular and other plates ; 

 and in rods, rings, and membranes. This secondary mode is 

 pointed out by the figures delineated by the lycopodium or 

 other light powder ; and as far as I can perceive, its existence 

 is assumed, or rather proved, exclusively from these forms. 

 Hence much of the importance which I attach to the present 

 paper. A secondary mode of division, so subordinate to the 

 principal as to be always superposed by it, might have great 

 influence in reasonings upon other points in the philosophy of 

 vibrating plates ; to prove its existence therefore is an important 

 matter. But its existence being assumed and supported by 

 such high authority as the name of Savart, to prove its non- 

 existence, supposing it without foundation, is of equal con- 

 sequence. 



6. The essential appearances, as far as I have observed 

 them, are as follows: Let the plate before mentioned (2), 

 which may be three or four inches square, be nipped and 

 held in a horizontal position by a pair of pincers of 

 the proper form, and terminated, at the part touching the 

 glass, by two pieces of cork ; let lycopodium powder be 

 sprinkled over the plate, and a violin bow be drawn down- 

 wards against the middle of one edge so as to produce a clear 

 full tone. Immediately the powder on those four parts of the 

 plate towards the four edges will be agitated, whilst that 

 towards the two diagonal cross lines will remain nearly or 

 quite at rest. On repeating the application of the bow several 

 times, a little of the loose powder, especially that in small 

 masses, will collect upon the diagonal lines, and thus, showing 

 one of the figures which Chladni discovered, will also show 

 the principal mode of division of the plate. Most of the 

 powder which remains upon the plate will, however, be col- 

 lected in four parcels ; one placed near to each edge of the 

 plate, and evidently towards the place of greatest agitation. 

 Whilst the plate is vibrating (and consequently sounding) 

 strongly, these parcels will each form a rather diffuse cloud, 

 moving rapidly within itself; but as the vibration diminishes, 

 these clouds will first contract considerably in bulk, and then 

 settle down into four groups, each consisting of one, two, or 

 more hemispherical parcels (53), which are in an extraordinary 



