MR. FARADAY ON A PECULIAR CLASS OF ACOUSTICAL FIGURES. 313 
occurred at the centres of oscillation, either by direct observation, or the 
reflection from its surface of right-lined figures, or by looking through the 
parts, as through a lens, at small print and other objects, failed. 
43. As however when the plate was strongly vibrated, the well-known and 
peculiar crispations which form on water at the centres of vibration, occurred 
and prevented any possible decision as to accumulation, it was only when these 
were absent and the vibration weak, and the accumulation therefore small, 
that any satisfactory result could be expected ; but as even then no appearance 
was perceived, it was concluded that the force of gravity combined with the 
mobility of the fluid was sufficient to restore the uniform condition of the 
layer of water after the bow was withdrawn, and before the eye had time to 
observe the convexity expected. 
44. To remove in part the effect of gravity, or rather to make it coincide 
with, instead of oppose the convexity, the under surface of the plate was moist- 
ened instead of the upper, and by inclining the plate a little. Fig. 9. 
the water made to hang in drops at a or b or c, fig. 9, at plea- 
sure. On applying the bow at x , and causing the plate to vibrate, 
the drops instantly disappeared, the water being gathered up and 
expanded laterally over the parts of the plate from which it had 
flowed. On stopping the vibration, it again accumulated in hanging drops, 
which instantly disappeared as before on causing the plate to vibrate, the force 
of gravity being entirely overpowered by the superior forces excited by the 
vibrating plate. Still, no visible evidence of convexity at the centres of vibra- 
tion were obtained, and the water appeared rather to be urged from the 
vibrating parts than to them. 
45. The tenacity of oil led to the expectation that better results would be 
obtained with it than with water. A round plate, held horizon- 
tally by the middle (6. 42), was covered with oil over the upper 
surface, so as to be flooded, except at x , fig. 10, and the bow ap- 
plied at X as before, to produce strong vibration. No crispation 
occurred in the oil, but it immediately accumulated at a , b, and c, 
forming fluid lenses there, rendered evident by their magnifying power when 
print was looked at through them. The accumulations were also visible on 
putting a sheet of white paper beneath, in consequence of the colour of the oil 
2 s 2 
