ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 963 
beyond which they approach each other until they coalesce in K, after 
which they again diverge until the plate N, which is parallel to the axis. 
The nodal system indicated by the dotted lines follows another 
course; the summits of the two curves which compose it at first recede 
from each other, but they soon reapproach each other, and these curves 
transform themselves into two straight lines in the plate E, where the 
curves of the other mode of division attain their maximum of recession: 
beyond this limit they separate, but in a perpendicular direction to 
that in which they approached, and they attain their maximum of 
recession towards the plate H, for which the two systems of curves are 
nearly similar: they afterwards approach each other, and like those of 
the other system, they transform themselves, in K, into two straight 
lines, which intersect each other at right angles. Lastly, starting from 
this point, they diverge again, until the plate N, for which the two 
systems again become equal, assuming, with respect to the axis of the 
erystal, a direction different from that which they had taken at I and at 
H. I must observe that my supply of rock crystal having failed at the 
end of my experiments, I have not been able to cut the plate K; but 
the transformations of the nodal lines so clearly indicate that there 
ought to be a plate which presents these modes of division, that I have 
not hesitated to admit its existence. 
The course which the two sounds follow, in this series of plates, is 
much more simple than that of the nodal figures: at first those of the 
dotted system become lower, commencing with the plate A, and pro- 
ceeding as far as the plate E, inclined 51° to the axis, and which gives 
the sound C like the plate No. 4, inclined the same number of degrees 
to the axis; afterwards the sound of this system gradually ascends until 
the plate N parallel to the axis, where it attains its maximum of eleva- 
tion. As to the sounds of the other series of modes of division, it is 
observed that they gradually ascend from the plate perpendicular to the 
axis unto K, in which the nodal systems both consist of lines crossed 
rectangularly, and that they afterwards descend again until the plate 
N parallel to the axis. It is obvious that it is not necessary to examine 
such plates as A’, B/, C', D’, fig. 4, since they ought to present the 
same phenomena as the corresponding plates A, B, C, D: only, that 
which was inclined to the right of the axis in the plates B, C, D is 
_ found inclined to the left in the plates B', C’, D’. 
Beet" 2 
There is none of the modes of division of this series which is not 
analogous to some one of those which have been presented to us by 
bodies in which there are evidently three rectangular axes of elasticity ; 
nevertheless, considered all together, the transformations we have just 
described present peculiarities which do not exist in the fourth series of 
i plates of wood, fig. 14, Pl. III. The most striking consists in this, that 
_in the transformations of this last series, none of the systems, except 
ay 
