330 On a Peculiar Class of Acoustical Figures. [1831. 



that any satisfactory result was to be expected ; but as even 

 then no appearance was perceived, it was concluded that the force 

 of gravity combined with the mobility of the fluid was sufficient 

 to restore the uniform condition of the layer of water after the 

 bow was withdrawn, and before the eye had time to observe 

 the convexity expected. 



44. To remove in part the effect of gravity, or rather to make 

 it coincide with, instead of oppose the convexity, the under 

 surface of the plate was moistened instead of the upper, and by 



Fig. 9. 



inclining the plate a little, the water made to 

 hang in drops at a or b or c, fig. 9, at pleasure. 

 On applying the bow at x , and causing the 

 plate to vibrate, the drops instantly disappeared, 

 the water being gathered up and expanded 

 laterally over the parts of the plate from which 

 it had flowed. On stopping the vibration, it 

 again accumulated in hanging drops, whicli instantly disap- 

 peared as before on causing the plate to vibrate, the force of 

 gravity being entirely overpowered by the superior forces 

 excited by the vibrating plate. Still, no visible evidence of 

 convexity at the centres of vibration were obtained, and the 

 water appeared rather to be urged from the vibrating parts 

 than to them. 



45. The tenacity of oil led to the expectation that better 

 results would be obtained with it than with water. A round 

 plate, held horizontally by the middle (6. 42), 

 was covered with oil over the upper surface, 

 so as to be flooded, except at x , fig. 10, and 

 the bow applied at x as before, to produce 

 strong vibration. No crispation occurred in 

 the oil, but it immediately accumulated at a, 

 b } and c, forming fluid lenses there, rendered 

 evident by their magnifying power when print was looked at 

 through them. The accumulations were also visible on putting 

 a sheet of white paper beneath, in consequence of the colour 

 of the oil being deeper at the accumulations than elsewhere ; 

 and they were also rendered beautifully evident by making the 

 experiment in sunshine, or by putting a candle beneath the 

 plate, and placing a screen on the opposite side to receive the 

 images formed at the focal distance. 



Fig. 10. 



