350 On the Forms and States of Fluids [ 1 83 i . 



107. I have thought it unnecessary to dwell upon the explana- 

 tion of the circular linear heaps (83. 93. 110) produced on long 

 or circular plates by feeble vibration. They are explicable 

 upon the same principles, account being at the same time taken 

 of the arrangement and proportion of vibrating force in the 

 various parts of the plates. 



108. The heaps which constitute crispation (as the word has 

 been used in this paper) are in form, quality, and motion of 

 their parts, the same with what are called stationary undula- 

 tions ; and if the mercury in a small circular basin be tapped 

 at the middle, stationary undulations, resembling the ring-like 

 heaps (83. 110), will be obtained; or if a rectangular frame be 

 made to beat at equal intervals of time on mercury or water, 

 heaps like those of the crispations, arranged quadrangularly at 

 angles of 45 to the frame, will be produced. These effects 

 are in fact the same with those described, but are produced by 

 a cause differing altogether. The first are the result of two 

 progressing and opposed undulations, the second of four : but 

 the heaps of crispations are produced by the power impressed 

 on the fluid by the vibrating plate ; are due to vibrations of 

 that fluid occurring in twice the time of the vibrations of the 

 plate ; and have no dependence on progressive undulations, 

 originating laterally, as many of the phenomena described prove. 

 Thus, when the edges were beveled (72. 110), or covered with 

 cloth, or wet sawdust, so that waves reaching the side should 

 be destroyed, or when the limits of the water or plates were 

 round (91) or irregular, still the heaps were produced, and 

 their arrangement square. When the round plate (93) was 

 used, regular crispations were still produced, though, as the 

 water extended over the nodal line, and was there perfectly 

 undisturbed, no progressing and opposed undulations could 

 originate to produce them. Vellum stretched over a ring, and 

 rendered concave by the pressure of the exciting rod, pro- 

 duced the same effect. 



109. When a plate of tin, rendered very slightly concave, 

 was attached to a lath (69), so as to have equality of vibratory 

 motion in all its parts, and a little dilute alkali (which would 

 wet the surface) put into it, the crispations formed in the mid- 

 dle, but ceased towards the sides, where, though well-wetted, 

 there was not depth enough of water, and whence also no 



