336 
MR. FARADAY ON THE FORMS AND STATES 
of the ridges pieces of cork oscillated from one ridge towards its neighbour, 
and back again. The lycopodium sometimes seemed to move on the ridges 
from the wood, and between them to it ; but the motion was irregular, and 
there was no general current outwards or inwards. There was not so much 
disturbance as amongst the heaps (90). 
117. Avery simple arrangement exhibits these ripples beautifully. If an 
oval or circular pan, fifteen or eighteen inches in diameter, be filled with 
water, and a piece of lath (69) twelve or fifteen inches long be held in it, edge 
upwards, so as to bear against the sides of the pan as supporting points, and 
cut the surface of the water, then on being vibrated horizontally by the glass 
rod and wet finger, the phenomenon immediately appears with ripples an inch 
or more in length. When the upper edge of the lath was an inch below the 
surface, the ripples could be produced. When the vessel had a glass bottom, 
the luminous figures produced by a light beneath and a screen above, were 
very beautiful (96). Glass, metal and other plates could thus be easily expe- 
rimented with. 
118. These ripple-like stationary undulations are perfectly analogous as to 
cause, arrangement and action with the heaps and crispations already ex- 
plained, i. e. they are the results of that vibrating motion in directions perpen- 
dicular to the force applied (105), by which the water can most readily accom- 
modate itself to rapid, regular, and alternating changes in bulk in the immediate 
neighbourhood of the oscillating parts. 
119. From this view of the effect it was evident that similar phenomena 
would be produced if a substance were made to vibrate in contact with and 
normally to the surface of a fluid, or indeed in any other direction. A lath 
was therefore fixed horizontally in a vice by one Fig. 29 . x 
end, so that the other could vibrate vertically ; a 
cork was cemented to the under surface of the free 
end, and a basin of water placed beneath with its . 
surface just touching the cork ; on vibrating the | 
lath by means of the glass rod and fingers (67), 
a beautiful and regular star of ridges two, three, or even four inches in length, 
was formed round the cork, fig. 29. These ridges were more or less numerous 
according to the number of vibrations, & c. As the water was raised, and more 
