538 



HISTORY OF SCIENCE. 



figures, indicating of course an equal variety of forms of vibrating 

 segments in the plates. 



The plates used in these experiments were generally made either 



FIG. 253. 



FIG. 254. 



of glass or of copper. The plate was supported horizontally by being 

 firmly fixed at one or more points by clamps ; and the figures varied 



according as the bow was applied 

 at one or another part of the 

 edge, and according as segments 

 were determined by touching the 

 plate at certain points with the 

 fingers. Thus, if a rectangular 

 plate was fastened at the centre, 

 and the bow was applied at the 

 middle of one of the sides, the 

 plate divided into four segments, 

 the diagonals of the square being 

 nodal lines (Fig. 254). Again, 



FIG. 255. 



FIG. 256. 



if a rectangular plate were handled in the manner shown in Fig. 255, 

 the formation of additional semicircular nodal lines was determined, 

 and the sand arranged itself into the symmetrical forms seen in the 

 figure. Many figures more curious than this are producible by slight 



