294 



Strehlke on the Acoustic Figures of Plates. 



resting point be nearly the same, in order to produce the same 

 figures. 



The lines were measured by a scale of sufficient accuracy, to 

 convince Professor Strehlke that the results were correct to the 

 2 l <jth f a line. 



One of the most simple acoustic figures, fig. 2, is formed 

 when three or four corners of the plate are supported, and 

 the bow is drawn at the middle of one of the sides : it may be 

 obtained by simply holding the plate with the left hand, 

 placing the thumb on E, fig. 1, the first finger on C, and 

 the little finger on D, and then drawing the bow along the 



Fig. l, 



Fig. 2. 



Fig. 3. 



Fig.4. 



middle of DF. On all regular plates of metal or glass the 

 figure will be found to be a hyperbola, the angles between the 

 principal axis and asymptotes of which exceed 45. The 

 direction of the principal axis cannot be determined previously 

 to the experiment ; but after it is found, it will be proper to 

 mark it down on the plate, as the direction of a great many 

 other figures is dependent on it. 



On three plates, two of brass and one of copper, the ordi- 

 nates were equally divided by the axis ; B was taken as the 

 commencement of the co-ordinates, and on the supposition 

 that the curve was a conic section of the equation 



?/ 2 = px + qx* ; 



the most probable value of the coefficients was determined by 

 the method of the least squares. 



In a square plate of brass (No. 1.) of 34.3 Parisian lines in 

 length, and l'".l thick, the equation deduced from the mea- 

 sured value of the co-ordinates was 



y* = 10836 . x(x + 6'".27), 



