[ 319 ] 
APPENDIX. 
On the Forms and States assumed by Fluids in contact with vibrating 
elastic surfaces. 
63. When the upper surface of a plate vibrating so as to produce sound (2. 6) 
is covered with a layer of water, the water usually presents a beautifully cris- 
pated appearance in the neighbourhood of the centres of vibration. This 
appearance has been observed by Oersted*, Wheatstone -f', Weber^;, and 
probably others. It, like the former phenomena which I have endeavoured 
to explain, has led to false theory, and being either not understood or 
misunderstood, has proved an obstacle to the progress of acoustical phi- 
losophy. 
64. On completing the preceding investigation, I was led to believe that the 
principles assumed would, in conjunction with the cohesion of fluids, account 
for these phenomena. Experimental investigation fully confirmed this expecta- 
tion, but the results were obtained at too late a period to be presented to the 
Royal Society before the close of the Session ; and it is only because the philo- 
sophy and the subject itself is a part of that received into the Philosophical 
Transactions in the preceding paper, that I am allowed, by the President and 
Council, the privilege of attaching the present paper in the form of an 
Appendix. 
65. The general phenomenon now to be considered is easily produced upon 
a square plate nipped in the middle, either by the fingers or the pincers (2. 6), 
held horizontally, covered with sufficient water on the upper surface to flow 
freely from side to side when inclined, and made to vibrate strongly by a bow ap- 
plied to one edge, X , fig. 12, in the usual way. Crispations appear 
on the surface of the water, first at the centres of vibration, and 
extend more or less towards the nodal lines, as the vibrations are 
stronger or weaker. The crispation presents the appearance of 
small conoidal elevations of equal lateral extent, usually arranged 
* Lieber’s Hist, of Natural Phenomena for 1813. f Annals of Philosophy, N. S. vi. p. 82. 
£ Wellenlehre, p. 414. 
2 T 
Fig. 12. 
MDCCCXXXI. 
