go THE CREATION OF MATTER 



through the centre at right angles to each other. This 

 division of the plate corresponds to the deepest tone. 

 Again sprinkling sand over the surface, and damping one 

 of the corners, and drawing a bow across the centre of one 

 of the sides, the experimenter sees the sand dancing over 

 the plate, and finally arranging itself along the diagonals. 

 The note produced is the fifth above the fundamental. 

 If two points be damped on one side, and a bow be drawn 

 across that opposite to it, a much shriller note is heard, 

 diagonal lines are formed, and the two nodes are joined 

 by a curve. By various dampings a great many beautiful 

 figures are drawn by the sand. Round plates also exhibit 

 regular motions. One is set horizontally on a stand, 

 blackened in colour, and fine white sand scattered over it. 

 If its edge be damped at any point, and a bow be drawn 

 across 45 distant, it yields its fundamental note, and the 

 sand arranges itself along two diameters. If the bow be 

 drawn across at the distance of 30 from the point damped, 

 the sand takes the form of a star, in which there are 

 six nodal lines, forming six segments. In some way the 

 plate may be divided into 8, 10, 12, 14, 16 segments. The 

 number is always even. As the divisions are multiplied, 

 the vibrations become more numerous, and the note is 

 raised in pitch. That given forth by sixteen sectors is 

 painful in its sharpness. 



Bells exhibit the phenomena of vibrating discs, and if 

 one be filled with water, and struck, music wavelets are 

 formed. 



Sound vibrations are also created in a longitudinal 

 direction in strings, rods, plates, and bells. They are 

 produced by a bow drawn obliquely over a string, or by 

 means of cloth or leather powdered with resin, and 

 drawn sharply along. An iron wire is attached to a 

 sounding board, and drawn tight at the other end. 



