OF FLUIDS ON VIBRATING ELASTIC SURFACES. 
321 
unlimited change of isochronous vibrations, from that producing a high note 
to those in which not more than five or six occurred in a second, could be 
obtained. The crispations were formed upon a glass plate attached to the 
middle of the lath, by two or three little pellets of soft cement*. 
70. Obtained in this way the appearances were very beautiful, and the faci- 
lities very great. A glass plate, from four to eight inches square, could be 
covered uniformly with crispations of the utmost regularity; for, by attaching 
the plate with a little method, and at points equidistant from the centre of the 
bar, it was easy to make every part travel with the same velocity, and in that 
respect differ from and surpass the bar which sustained it. The conoidal heaps 
constituting the crispation could be so enlarged by slowness of vibration, that 
three or four occupied a linear inch. The glass plate could be removed, and 
another of different form or substance, and with other fluids, as mercury, &c., 
substituted in an instant. 
71. In using laths, it is necessary to confine the parts bearing upon the 
bridges, either by slight pressure of the fingers, or by loops of string, or by 
weights. The exciting glass rod need not necessarily rest upon the middle of 
the bar or plate, but may be applied with equal effect at some distance from 
it. Long laths may be made to subdivide in their mode of vibration, accord- 
ing as the rod is applied to different places, and the pressure given by the ex- 
citing moist fingers is varied ; with each change of this kind an immediate 
change of the crispation is observed. 
72. This form of apparatus was enlarged until a board eighteen feet long 
was used, the layer of water being now three fourths of an inch in depth and 
twenty-eight inches by twenty inches in extent. The sides of the cistern were 
very much inclined, so that the water should gradually diminish in depth, and 
thus reflected waves be prevented. The vibrations were so slow as to be pro- 
duced by the direct application of the hand, and the heaps were each from an 
inch to two inches in extent. Though of this magnitude, they were identical 
in their nature with those forming crispations on so small a scale as to appear 
merely like a dullness on the surface of the water. 
73. In these experiments the proportion of water requires a general adjust- 
ment, the crispations being produced more readily and beautifully when there 
* Equal parts of yellow wax and turpentine. 
2 t 2 
