255 
ARTICLE XI. 
Researches on the Elasticity of Bodies which Crystallize 
regularly ; by Fevix SAVART. 
(Read to the Academy of Sciences of Paris, January 26th, 1829.) 
From the Annales de Chimie et de Physique, vol. xu. p..5, et seq. 
{Continued from p. 152.] 
§ Ill. Analysis of Rock Crystal by means of Sonorous Vibrations, 
OCK Crystal most ordinarily occurs under the form of a hexahedral 
prism, terminated by pyramids with six faces (fig. 1. pl. IV.). Although 
this substance does not admit of cleavage by the ordinary means, it is 
assumed, from analogy, that its primitive form is a rhombohedron, like 
that which would be obtained if the crystal were susceptible of cleavage 
parallel to the three non-adjacent faces of the pyramid, such, for ex- 
ample, as aX 6, eX f, e Xd, and their parallels a! Y b', e' Y f', c' Yd’. The 
accuracy of this induction is besides confirmed by a very simple expe- 
riment, which consists in making a prism of rock crystal red hot, and 
suddenly cooling it; an operation which determines its fracture, and 
which most frequently, gives as the result pieces of crystal which have 
the form of rhombohedrons. 
Setting out with these notions with which mineralogy furnishes us, 
it is obvious that circular plates taken parallel or perpendicular to the 
axis, parallel to a face of cleavage or of non-cleavage of the pyramid, &c. 
ought to present different phenomena with respect to sonorous vibra- 
tions, since the cohesion and elasticity are not the same in these dif- 
ferent directions. Consequently, to simplify as much as possible the 
examination of these phenomena, we have had cut, from different 
pieces of rock crystal, a considerable number of circular plates, at first 
taken in different azimuths of a plane perpendicular to the axis, fig. 2. 
and fig. 2, bis; then, according to the azimuths of a plane perpendicular 
to two parallel faces of the hexahedron, and passing through its axis, 
fig. 3.and fig. 3, bis; lastly, according to the different azimuths of a plane 
passing through the axis and two opposite edges of the crystal fig. 4. 
and 4: bis. 
As it was necessary to support this general disposition of the expe- 
riments by facts, it was indispensable to ascertain first, that the elastic 
state of the crystal is the same for all the planes parallel to the natural 
faces of the hexahedron, and next, that it is also the same for all the 
