OF FLUIDS ON VIBRATING ELASTIC SURFACES. 
323 
structure), which tends to restore its particles to their first position, and co- 
existing with great freedom to move through small spaces, whilst that of oil 
is due to a real difficulty in removing the particles one by another. It is pos- 
sible that the power of assuming, more or less readily, the crispated state may 
be a useful and even important indication of the internal constitution of dif- 
ferent fluids. 
77. With mercury the crispations are formed with great facility, and of 
extreme beauty, when a piece of amalgamated tin or copper plate being fixed 
on a lath (69), is flooded with the fluid metal, and then vibrated. A film quickly 
covers the metal, and then the appearances are not so regular as at first ; but 
on removing the film by a piece of paper, their regularity and beauty are re- 
stored. It is more convenient to cover the mercury with a little very dilute 
acetic or nitric acid ; for then the crispations may be produced and maintained 
for any length of time with a surface of perfect brilliancy. 
78. When a layer of ink was put over the mercury, the acid of the ink 
removed all film, and the summits of the metallic heaps, by diminishing the 
thickness of the ink over them, became more or less visible, producing the ap- 
pearance of pearls of equal size beautifully arranged in a black medium. When 
mercury covered with a film of dilute acid was vibrated in the sunshine, and 
the light reflected from its surface received on a screen, it formed a very 
beautiful and regular image ; but the screen required to be placed very near 
to the metal, because of the short focal lengths of the depressions on the mer- 
curial surface. 
79. It is sometimes difficult to arrive by inspection at a satisfactory conclu- 
sion of the forms and arrangements thus presented, because of multiplied 
reflection and the particular condition of the whole, which will be described 
hereafter (95). When observed, well formed with vibrations so slow as to pro- 
duce three or four elevations in a linear inch (70), they are seen to be conoidal 
heaps rounded above, and apparently passing into each other below by a cur- 
vature in the opposite direction. When arranged regularly, each is surrounded 
by eight others, so that, a single light being used, nine images may be sent from 
each elevation to the eye. These are still further complicated, when trans- 
parent fluids are used, by reflections from the glass beneath. The use of ink 
