336 On the Forms and States of Fluids [1831. 



65. The general phenomenon now to be considered is easily 

 produced upon a square plate nipped in the middle, either by 

 the fingers or the pincers (2. 6), held horizontally, covered with 

 sufficient water on the upper surface to flow freely from side to 

 side when inclined, and made to vibrate strongly by a bow applied 

 to one edge, x , fig. 12, in the usual way. Fig. 12. 

 Crispations appear on the surface of the water, 

 first at the centres of vibration, and extend 

 more or less towards the nodal lines, as the 

 vibrations are stronger or weaker. The cris- 

 pation presents the appearance of small co- 

 noidal elevations of equal lateral extent, usually 

 arranged rectangularly with extreme regularity ; permanent* 

 (in appearance), so long as a certain degree of vibration is sus- 

 tained ; increasing and diminishing in height, with increased 

 or diminished vibration ; but not affected in their lateral extent 

 by such variations, though the whole crispated surface is en- 

 larged or diminished at those times. If the plate be vibrated, 

 so as to produce a different note, the crispations still appear at 

 the centre of vibration, but are smaller for a high note, larger 

 for a low one. The same note produced on different sized 

 plates, by different modes of vibration, appears to produce 

 crispations of the same dimension, other circumstances being 

 the same. 



66. These appearances are beautifully seen when ink diluted 

 with its bulk of water is used on the plate. 



67. It was necessary, for examination, both to prolong and 

 enlarge the effect, and the following were found advantageous 

 modes of producing it. Plates of crown-glass, from eighteen 

 to twenty-two inches long, and three or four inches wide, were 

 supported each by two triangular pieces of wood acting as 

 bridges (18), and made to vibrate by a small glass rod or tube 

 resting perpendicularly at the middle, over which the moist 

 fingers were passed. By sprinkling dry sand on the plates, 

 and shifting the bridges, the nodal lines were found (usually 

 about one-fifth of the whole length from each end), and their 

 places marked by a file or diamond. Then clearing away the 

 sand, putting water or ink upon the plate, and applying the rod 

 or fingers, it was easy to produce the crispations and sustain 



* Weber's Wellenlehre, p. 414. 



