1831.] on Vibrating Elastic Surfaces. 345 



but constant for any particular position and velocity of vibra- 

 tion. Upon placing the light and the eye in positions nearly 

 perpendicular to the general surface of the fluid, so as to avoid 

 the direct influence of the motion of vibration, still the lumi- 

 nous, linear, endless figure was produced, extending more or 

 less in different directions, according to the relation of the 

 light and eye to the crispated surface, and occasionally corre- 

 sponding in its extent one way to the width of the heap, i. e. to 

 the distance between the summit of one heap and its neigh- 

 bours, but never exceeding it. The figure produced by one heap 

 was accurately repeated by all the heaps when the vibrating 

 force of the plate was equal (70) and the arrangement regular. 



95. The view which I had been led to anticipate of the 

 nature of the heaps, from the effects described in the former 

 paper, were, that each heap was a permanent elevation, like 

 the cones of lycopodium powder (53. 58), the fluid rising at the 

 centre, but descending down the inclined sides, the whole 

 system being influenced, regulated, and connected by the cohe- 

 sive force of the fluid. But these characters of the reflected 

 image, with others of the effects already described, led to the 

 conclusion, that notwithstanding the apparent permanency of 

 the crispated surface, especially when produced on a small 

 scale, as by the usual method, the heaps were not constant, 

 but were raised and destroyed with each vibration of the plate ; 

 and also that the heaps did not all exist at once, but (referring 

 to locality) formed two sets of equal number and 

 arrangement, fig. 23, never existing together, 



but alternating with, and being resolved into 



each other, and by their rapidity of recurrence 



giving the appearance of simultaneous and even 



permanent existence. Provided this view were 



confirmed, it seemed as if it would be easy to 



explain the production of the heaps, their regular arrangement, 



&c., and to deduce their recurrence, dimensions, and many 



other points relative to their condition. 



96. On producing a water crispation, having four or five 

 heaps in a linear inch, placing a candle beneath, and a screen 

 of French tracing-paper above it, the phenomena were very 

 beautiful, and such as supported the view taken. By placing 

 the screen at different distances, it could be adapted to the 



