262 FELIX SAVART’S RESEARCHES ON THE 
PL. 1V.; 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, Pl. III.; No. 4 in the crystal would correspond to No.3 in the 
wood; and lastly, No. 11 of the crystal plates, in which a second maxt- 
mum of recession of the summits of the hyperbola occurs, would corre- 
spond to No.6 of the plates of wood; so that the same phenomena, 
which are included, in a body having three rectangular axes of elas- 
ticity, in an arc only of 90°, to be afterwards reproduced in a contrary 
direction in the following quadrant, are included in rock erystal in an 
are of 96° 0’ 13", and cannot be entirely reproduced, because similar 
phzenomena to those we have just observed for a series of plates cut 
round a, fig. 1, Pl. 1V., occurring, for the same degrees of inclination, in 
the two series of plates which might be cut round ed and ef, both are 
confounded together in the vicinity of the plate perpendicular to XY. 
Turrp Series. Plates cut round the diagonal ac, fig.1, and accord- 
ing to the different Azimuths of the Plane be! Yb'e X, fig. 4. 
These plates present phenomena 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 which passes through the two opposite edges of the 
hexahedron ought to participate in the properties of both. Itis thus that 
the plates perpendicular to two parallel faces of the 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 each other, I have 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 «x y of the axis parallel to the 
axis X Y of fig.1, I have here supposed that the crystal had been 
turned round until its edge 6 e! was in front. This is besides suffi- 
ciently indicated by figure A, which 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.... shows that the nodal system 
indicated by the perfect lines is formed of two hyperbolic branches 
which 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, 
