344 On the Forms and States of Fluids [1831. 



91. The crispations are much influenced by various circum- 

 stances. 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 un- 

 steady, often breaking up and starting by pieces into different 

 and changing positions. 



92. When mercury was used (77), the film formed on it after 

 a few moments 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. These and many other experi- 

 ments (83) showed that the direction and nature of the vibra- 

 tion 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. 



94. The beautiful appearance exhibited when the crispations 

 are produced in sunshine, or examined by a strong concen- 

 trated artificial light, has been already referred to (78, 79). 

 When the reflected image from any one heap is examined (for 

 which purpose ink (75) or mercury (77) is very convenient), it 

 will be found not to be stationary, as would happen if the heap 

 was permanent and at rest ; nor yet to form a vertical line as 

 would occur if the heap were permanent but travelled to and 

 fro with the vibrating plate ; but it moves so as to re-enter 

 upon its course, forming an endless figure, like those produced 

 by Dr. Young's piano-forte wires, or Wheatstone's kaleido- 

 phone, varying with the position of the light and the observer, 



