1831.] on Vibrating Elastic Surfaces. 339 



cury, the different degrees of colour or translucency corre- 

 sponding to different depths of the fluid, give important infor- 

 mation relative to the true nature of the phenomena (78. 85. 97). 

 Milk is, for its opacity, of similar advantage, especially when a 

 light is placed beneath ; and being more viscid than water, is 

 better for large arrangements (72.98), because it produces less 

 splashing. 



76. Oil does not show small crispations readily (120), and 

 was supposed to be incapable of forming them, but when 

 warmed (by which its liquidity is increased) it produces them 

 freely. Cold oil will also produce large crispations, and for 

 very large ones would probably be better than water, because 

 of its cohesion. The difference between oil and white of egg 

 is remarkable ; for the latter, from common observation, would 

 appear to be a thicker fluid than oil : but the qualities of cohe- 

 sion differ in the two, the apparent thickness of white of egg 

 depending upon an elastic power (probably due to an approach 

 to 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 re- 

 moving the particles one by another. It is possible 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 different fluids. 



77. With mercury the crispations are formed with great 

 facility, and of extreme beauty, when a piece of amalgamated 

 tin or copper plate, 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 restored. 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, be- 

 came more or less visible, producing the appearance of pearls 

 of equal size beautifully arranged in a black medium. When 

 mercury covered with a film of dilute acid was vibrated in the 



