OF FLUIDS ON VIBRATING ELASTIC SURFACES. 
327 
pation, it moved about over the fluid in every possible direction, whilst 
the crispations existed of the utmost steadiness beneath. The same thing 
occurred with pieces of cork on very large crispations (98). But when much 
lycopodium was put on, so that the particles retained each other in a steady 
position, then it formed lines * parallel to the arrangement of the heaps, the 
powder being displaced from the parts over the heaps, and taking up an 
arrangement perpendicularly over the sand beneath. As the lycopodium forms 
float on the water they are easily disturbed, and in no respect approach as to 
beauty and utility to the forms produced by the sand ; but lycopodium may 
be used with smaller crispations than sand. 
91. The crispations are much influenced by various circumstances. They 
tend to commence at the place of greatest vibration ; but if the quantity of 
fluid is too little there, and more abundant elsewhere, they will often commence 
at the latter place first. Their final arrangement is also much affected by the 
form of the plate, or of the pool of water on which they occur. When the 
plates or pools are rectangular, and all parts vibrate with equal velocity, the 
lines of heaps are at angles of 45° to the edges. But when semicircular and 
other plates were used, the arrangement, though quadrangular, was unsteady, 
often breaking up and starting by pieces into different and changing posi- 
tions. 
92. When mercury was used ( 77 ), the film formed on it after a few mo- 
ments had great power, according to the manner in which it was puckered, 
of modifying the general arrangement of new crispations. 
93. When a circular plate, supported by cork feet attached where a single 
nodal line would occur, was covered with water and vibrated by a rod resting 
upon the middle, the crispations extended from the middle towards the nodal 
line ; these were sometimes arranged rectangularly, but had no steadiness of 
position, and changed continually. At other times the heaps appeared as if 
hexagonal, and were arranged hexagonally, but these also shifted continually. 
This and many other experiments (83) showed that the direction and nature of 
the vibration of the plate (i. e. of the lines of equal or varying vibrating force), 
had a powerful influence over the regularity and final arrangement of the 
crispations. 
MDCCCXXXI. 
* Wheatstone. 
2 u 
