OF FLUIDS ON VIBRATING ELASTIC SURFACES. 
329 
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 arrange- 
ment, &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 focal length 
due to the curvature at different parts of the surface of fluid, so that by ob- 
serving the luminous figure produced and its transitions as the screen was 
moved nearer or further, the general form of the surface could be deduced. 
Each heap with a certain distance of screen gave a star of 
light ©, fig. 24, which twinkled, i. e. appeared and disap- 
peared alternately, as the heap rose and fell. At the corners 
X equidistant from these, fainter starred lights appeared ; 
and by putting the screen nearer to or further from the sur- 
face, lines of light, in two or even four directions, appeared 
intersecting the luminous centres and apparently permanent, whilst circum- 
stances remained unchanged. These effects could be magnified to almost any 
scale (72). 
97- When heaps of similar magnitude were produced, with diluted ink on 
glass (75), and white paper or an illuminated screen looked at through them, a 
chequered appearance was observed. In one position, lines of a Fig. 25. 
certain intensity separated the heaps from each other, but the 
square places representing the heaps looked generally lighter. 
In another position, when but little reflected light came from 
the surface of the heaps, their places could be perceived as dark, 
from the greater depth of ink there. By care, another position could be found 
in which the whole surface looked like an alternate arrangement of light and 
dark chequers, fig. 25, not steady, but with a quivering motion, which further 
attention could trace as due to a rapid alternation in which the light spaces 
became dark and the dark light, simultaneously. When, instead of glass, a 
bright tin plate was used under the diluted ink, the chequered spaces and their 
alternations could be seen still more beautifully. 
98. It was in consequence of these effects that very large arrangements were 
2 u 2 
