EXPERIMENTS ON THE VIBRATIONS OF PLATES. 369 



For these experiments two plates are required one square, the 

 itlier circular, 12 cm in diameter cut from thin window glass of 

 miform thickness ; also a violin bow. Both plates, of which the 

 quare one should be cut by a glazier, while the second one may be 

 >repared by the student with the help of pastille, must have their 

 /dges well ground and rounded off upon the grindstone, or they 

 v^ould cut the hairs of the bow. In order to hold them, a large 

 , crew-clamp is secured to the table by means of a smaller one, as 

 hown in fig. 218. A cork from 15 to 20 mm high, somewhat tapering 

 iowards the upper end, which is about 8 mm wide, is placed below 

 lie point of the screw of the larger clamp, and the plate is supported 



FIG. 218 (an. prey: | real ,sL~ 



the cork. Upon the upper side of the plate a little round disc of 

 k is laid, also 8 mm wide and 2 or 3 mm thick, and the screw is 

 in turned clown so as to fix the whole moderately firmly together. 



Let the square plate thus fixed be touched at a (fig. 

 N) with the finger and at b with the well-rosined bow. 

 'aw the bow nearly straight downwards, and the figure 

 educed will be that shown in fig. 218, viz,, a rectan- 

 .lar cross, of which the four arms are parallel to the 

 les of the plate. The note given out is in this case 



B B 



