PHILOSOPHICAL TRANSACTIONS. 
I. On the Circulation of A ir observed in Kundt’s Tubes, and on some Allied Acoustical 
Problems. 
By Lord Rayleigh, D.C.L., F.P.S. 
Received October 23,—Read November 15, 1883. 
Experimenters in Acoustics have discovered more than one set of phenomena 
apparently depending for their explanation upon the existence of regular currents of 
air, resulting from vibratory motion, of which theory has as yet rendered no account. 
This is not, perhaps, a matter for surprise, when we consider that such currents, 
involving as they do circulation of the fluid, could not arise in the absence of friction, 
however great the extent of vibration. And even when we are prepared to include in 
our investigations the influence of friction, by which the motion of fluid in the neigh¬ 
bourhood of solid bodies may be greatly modified, we have no chance of reaching an 
explanation, if, as is usual, we limit ourselves to the supposition of infinitely small 
motion and neglect the squares and higher powers of the mathematical symbols by 
which it is expressed. 
In the present paper three problems of this kind are considered, two of which are 
illustrative of phenomena observed by Faraday. * In these problems the fluid may 
be treated as incompressible. The more important of them relates to the currents 
generated over a vibrating plate, arranged as in Chladni’s experiments. 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. 
This was traced by Faraday to the action of currents of air, rising from the plate at 
* “ On a Peculiar Class of Acoustical Figures; and on certain Forms assumed by gi’oups of particles 
upon Vibrating Elastic Surfaces,” Phil. Trans., 1831, p. 299. 
MDCCCLXXXIY. B 
