1831.] on Vibrating Elastic Surfaces. 351 



waves could be reflected to produce stationary undulations in 

 the ordinary manner. 



110. When a similar arrangement was made with mercury 

 on a concave tin plate, the effects were still more beautiful and 

 convincing. The centre portion was covered with one regular 

 group of quadrangular crispations ; at some distance from 

 the centre, and where the mercury was less in depth, these 

 passed into concentric, ring-like heaps, of which there were a 

 great many ; and outside of these there was a part wet with 

 mercury, but with too little fluid to give either lines or heaps. 

 Here there could be no reflected waves ; or, if that were thought 

 possible, those waves could not have formed both the circular 

 rings and the square crispation. When this plate was vibrated, 

 the mercury spread in all directions up the side ; a natural 

 consequence of the production of powerful oscillations at the 

 middle, which would extend their force laterally, but quite 

 against their being due to the opposition and crossing of waves 

 originating at the sides. 



111. A limited depth of fluid is by no means necessary to 

 produce crispations on the surface (73). A circular glass basin 

 about five inches in diameter and four inches deep was attached 

 to a lath (69), filled with water and vibrated, the exciting rod 

 being applied at the side (71). The surface of the water was 

 immediately covered with the most regular crispations, i. e. 

 heaps arranged quadrangularly. On taking out part of the 

 water and filling it up with oil, the oil assumed the same super- 

 ficies. On putting an inch in depth of mercury under the water, 

 the mercury became crispated. The experiment was finally 

 made with water fourteen inches in depth. Particles at a very 

 moderate depth in the water seemed to have no motion except 

 the general motion of the fluid, and the whole of the lower 

 part of the water may be considered as performing the part of 

 a solid mass upon which the superficial undulating portion 

 reposed. In fact, it matters not to the fluid, what is beneath, 

 provided it has sufficient cohesion, is uniform in relation to the 

 surface fluid, and can transmit the vibrations to it in an undis- 

 turbed manner*. 



* I have seen the water in a pail placed in a barrow, and that on the head 

 of an upright cask in a brewer's van passing over stones, exhibit these 

 elevations. 



