300 Strehlke on the Acoustic Figures of Plates. 



In AD A' it was necessary to incline D D' towards C C', in 

 order to divide the ordinate equally, the co-ordinates were con- 

 sequently not quite perpendicular. It was found that 



2/ = 0-4989 .#.(& + 33"'-005), 

 from which y was calculated with the following result, 



In the curve B D' B', the co-ordinates were perfectly per- 

 pendicular, and the equation deduced was 



2/ 2 = 1-001 . x (x + 15"'*14), 



which shows a very great difference of elasticity on the two 

 sides of the plate ; the centre of the plate was also almost by 

 0"'-6 nearer to D' than to D. 



In the same curve, on the brass plate No. 2, the equation 

 for A C B was found to be 



y* = 0-445 . x (x + 24"'-459), 

 and for A' C' B' 



2/ 2 = 0-4002 .x(x + 28"'-597) ; 



where the results of calculation and observation were also 

 found to correspond. 



The other acoustic figures consist merely of a repetition of 

 the above "curves. Fig. 8 consists of four squares, each of 

 which contains Fig. 2, and will be obtained by supposing the 

 plate at F and D' (Fig. 3), or C and E (Fig. 1), at the centre 

 of any of the four squares. The direction of the principal 

 axes will be parallel to that of A B in Fig. 2 ; the asymptotes 

 of the inner hyperbolas become also hyperbolic curves, so that 

 the whole figure might be constructed a priori, provided the 

 elasticity is perfectly equal ; if not, some of the hyperbolas 

 will have their axes perpendicular to the direction of A B in 

 Fig. 2. 



The measurement 6f the curves was made on a square brass 

 plate, 53"'-63 in length, and 0'"'7 thick. The line F T', which 



