372 EXPERIMENTS ON THE VIBRATIONS OF PLATES. 



"They behave precisely like flat plates, and are most easily 

 .divided, by means of two lines at right angles to one 

 another, into four vibrating parts. 



.Fir,. 221 (i real size). 



A vase of glass, or a common glass cup with a foot, may be made to 

 sound by drawing a violin bow across the edge at any one point, or 

 by rubbing the edges with a damp finger, applying gentle pressure. 

 In this manner four vibrating portions are always obtained. If the 

 whole is to be divided into six or eight vibrating parts, two points 

 must be touched by the fingers which are respectively -J-th or |th of 

 the circumference apart, and the bow must be applied at a point 





real size). 



which is T \th or T \rtli of the circumference distant from one of the 

 points at which the fingers are placed. The division into vibratinu 

 portions is rendered visible by filling the vase to about two-thirds 

 with water or alcohol. If alcohol be used, the finger must also b( 

 moistened with alcohol ; if the bow is used instead of the finger tin; 

 polish of the wood should be protected, by wrapping paper over it 

 against being splashed with the alcohol, which would spoil it. 



The vibrations of the glass sides are communicated to the liquid ! 

 and the surface becomes agitated by delicate waves and divided int< 

 four wavy areas, each bounded by an arc of a circle correspond^ 

 to the nodal lines of plates. The middle of one arc is always under 

 neath the bow or the finger ; if the bow is used the whole liqure i 

 stationary, but if the edge be rubbed by the finger the figure move 



