262 FELIX savart's kesearches on the 



PI. IV.; for, supposing several intermediate plates between Nos. 3 and 4^ 

 that which would be inclined 57° to the axis would correspond to No. 1 

 of fig. 8, PI. III.; No. 4 in the ciystal would correspond to No. 3 in the 

 wood ; and lastly, No. 11 of the crystal plates, in which a second 7naxi- 

 mum of recession of the summits of the hyperbola occui's, would corre- 

 spond to No. 6 of the plates of wood ; so that the same phaenomena, 

 which are included, in a body having three rectangular axes of elas- 

 ticity, in an arc only of 90°, to be aftenvards reproduced in a contrary 

 direction in the following quadrant, are included in rock crystal in an 

 arc of 96° 0' 13", and cannot be entirely reproduced, because similar 

 phaenomena to those we have just observed for a series of plates cut 

 round a b, fig. 1 , PI. IV., occurring, for the same degrees of inclination, in 

 the two series of plates which might be cut round c d and ef, both are 

 confounded together in the vicinity of the plate perpendicular toXY. 



Third Series. Plates cut round the diagonal ac,Jlg. 1, and accord- 

 ing to the different Azimuths of the Plane b e' Yb' e X,fig. 4. 



These plates present phaenomena much more complicated than those 

 of the two preceding series. It may be easily conceived that this 

 ought to be the case, since the plates parallel to the two adjacent faces 

 of the pyramid assume very different modes of division, which supposes 

 that their elastic state also greatly differs: consequently the plates perpen- 

 dicular to the plane M'hich passes through the two opposite edges of tlie 

 hexahedron ought to participate in the properties of both. It is thus that 

 the plates perpendicular to two parallel faces of tlie prism, and passing 

 through its axis, assume a disposition of nodal lines in which the direc- 

 tion of the planes of cleavage, parallel to one of the faces of the pyra- 

 mid, exercises a considerable influence. 



In the plates of this series (fig. 4, bis,) neither mode of division is 

 constant ; nevertheless, in order that they may be easily distinguished 

 from eacli other, I Jiave continued to indicate them, one by uninter- 

 rupted lines, the other by dotted lines. And for the purpose of pre- 

 serving, in all the plates, the projection xi/ of the axis parallel to the 

 axis XYof fig. 1, I have here supposed that the crystal had been 

 turned round until its edge b e' was in front. This is besides suffi- 

 ciently indicated by figure A, wliich represents the modes of division 

 of the plate perpendicular to the axis, as it also does the section of the 

 hexahedron by a plane parallel to this plate. 



The inspection of figures A, B, C, D, E. . . . shoAvs that the nodal system 

 indicated by the perfect lines is fonued of two hyperbolic branches 

 AA-hich at first straighten themselves, and the summits of which recede 

 more from each other, so far as the plate E inclined 51° to the axis. 



