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VII. On the Crispations of Fluid resting upon a Vibrating Sup- 
port. By Lord Rayleigh, D. C.L., F.R.S., Cavendish Pro- 
fessor of Physics in the University of Cambridge* '. 
IF a glass plate, held horizontally, and made to vibrate as 
for the production of Chladni's figures, be covered with 
a thin layer of water or other mobile liquid, the phenomena 
in question may be readily observed. Over those parts of the 
plate which vibrate sensibly the surface of the liquid is ruffled 
by minute waves, the degree of fineness increasing with the 
frequency of vibration. The same crispations are observed on 
the surface of liquid in a large wine-glass or finger-glass 
which is caused to vibrate in the usual manner by carrying 
the moistened finger round the circumference. All that is 
essential to the production of crispations is that a body of 
liquid with a free surface be constrained to execute a vertical 
vibration. It is indifferent whether the origin of the motion 
be at the bottom, as in the first case, or, as in the second, be due 
to the alternate advance and retreat of a lateral boundary, to 
accommodate itself to which the neighbouring surface must 
rise and fall. 
More than fifty years ago the nature of these vibrations was 
examined by Faraday with great ingenuity and success. His 
results are recorded in an Appendix to a paper on a Peculiar 
Class of Acoustical Figuresf, headed a On the Forms and 
States assumed by Fluids in Contact with vibrating Elastic 
Surfaces." In more recent times Dr. L. Matthiessen has 
travelled over the same ground \, and on one very important 
point has recorded an opinion in opposition to that of Faraday. 
In order more completely to satisfy myself, I have lately 
repeated most of Faraday's experiments, in some cases with 
improved appliances, and have been able to add some further 
observations in support of the views adopted. 
The phenomenon to be examined is evidently presented in 
its simplest form when the motion of the vibrating horizontal 
plate on which the liquid is spread is a simple up-and-down 
motion without rotation. To secure this, Faraday attached 
the plate to the centre of a strip of glass or lath of deal, sup- 
ported at the nodes, and caused to vibrate by friction. In 
my experiments an iron bar was used about 1 metre long and 
'0064 metre thick (in the plane of vibration). The bar was 
supported horizontally at the nodes ; and to its centre a glass 
plate was attached by gutta-percha and carefully levelled. 
* Communicated bv the Author. 
t Phil. Traus. 1831. 
1 Pogg. Ann, t. exxxiv. 1868, t. cxli. 1870. 
