255 



Articlk XI. 



Researches an the Elasticity of Bodies tvhich Crystallisie 

 regularly ; by Felix Savart. 



(Read to the Academy of Sciences of Paris, January 26th, 1829.) 



From the Annales dc Ckimie et de Physique, vol. xl. p. 5, et seq. 



[Continued from p. 152.] 



§ III. Analysis of Rock Crystal hy means of Sonorous Vibrations, 



JtvOCK Crystal most ordinarily occurs under the form of a hexahedral 

 prism, terminated by pyramids with six faces (fig. 1 . pi. 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 a X 6, eXf cXd, and their parallels a' Yi',e'Y/', 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 phsenomena 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 phaenomena, 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 crj'stal 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 



