1831.] 



on Vibrating Elastic Surfaces. 



341 



nearly so, and the exciting rod resting in the middle of it. 

 Ring-like linear heaps concentric to the exciting rod first 

 form to the number of six or seven ; these may be retained by 

 a moderated state of vibration, and produce intervals which 

 measured across the diameter of the rings are to the number 

 of ten in three inches, with a certain constant depth of water. 

 15y increasing the force of vibration, the altitude of these ele- 

 vations increases, but not their lateral dimension; and then linear 

 heaps form across these circles and the plate, and parallel to 

 the bridges, having an evident relation to the manner in which 

 the whole plate vibrates. These, which like all other of these 

 phenomena are strongest at the part most strongly vibrating, 

 soon break up the circles, and are themselves broken up, produ- 

 cing independent heaps, which at first are irregular and change- 

 able, but soon become uniform and produce the quadrangular 

 order ; first at angles of 45 to the edges of the plate, but gra- 

 dually moving round until parallel to them. So the arrange- 

 ment continues, unless the force be so violent as to break it up 

 altogether : if the vibratory force be gradually diminished, then 

 the heaps as gradually fall, but without returning through the 

 order in which they were produced. The following lines may 

 serve to indicate the course of the phenomena. 



Fig. 14. 



When perfectly formed, the heaps are also to the number of 

 ten in three inches with the same depth of water as that which 

 produced the rings. The intervals between the rings and the 

 heaps are the same, other influential circumstances remaining 

 unaltered. 



84. Another form of heaps occasionally occurred, but always 

 passing ultimately into those described. These heaps were 

 grouped in an arrangement still very nearly rectangular, 

 and at angles of 45 to the sides of the plate, but were con- 

 tracted in one direction, and elongated in the other ; these 

 directions being parallel to the sides and ends of the plate. 



