300 MR. FARADAY ON A PECULIAR CLASS OF ACOUSTICAL FIGURES. 
shows a division of the sounding plate into parts, all of which vibrate isochro- 
nously, 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 anticipated 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.” 
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 exist- 
ence 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 
consequence. 
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 
downwards 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 dis- 
