268 SAVART ON THE ELASTICITY OF CRYSTALLIZED BODIES. 



which tlie plates do not break clean off; for there is, it is well known, an 

 obvious difference in the manner in which sulphate of lime breaks ac- 

 cording to one direction or the other. We will, on concluding, re- 

 mark, that these modes of division are precisely the same as those of a 

 disc of rock crystal parallel to the axis and perpendicular to two faces 

 of the hexahedron, and that the mean of the optic axes in sulphate of 

 lime occupies in it the same position relatively to the nodal curves, as 

 the projection of the single axis of rock crystal assumes in that of the 

 plates of this substance of which we have just spoken. (See fig. 2, bis, 

 No. 3.) 



The preceding researches are, doubtless, far from deserving to be^ 

 considered as a complete examination of the elastic state of rock crystal 

 and of carbonate of lime ; nevertheless we hope they will be sufficient 

 to show that the mode of experiment we have employed may hereafter 

 become a powerful means of studying the structure of solid bodies, 

 regularly or even confusedly crystallized. Thus, for instance, the 

 relations which exist between the modes of division and the primi- 

 tive form of crystals allow us to presume that the primitive form of 

 certain substances which do not at all yield to a mere mechanical 

 division may be determined by sonorous vibrations. It is equally 

 natural to think that less imperfect notions respecting the elastic state 

 and cohesion of crystals than those Ave now possess, may throw light 

 upon many peculiarities of crystallization : for example, it is not im- 

 possible that the degrees of elasticity of a determinate substance may 

 not be exactly the same, for the same direction referred to the primitive 

 form, when the secondary form is different ; and, if it be so, as some 

 facts induce me to suspect, the determination of the elastic state of 

 crystals will lead to the explanation of the most complicated pheeno- 

 mena of the structure of bodies. Lastly, it appears that the comparison 

 of the results furnished concerning the constitution of bodies, on the 

 one hand by means of light, and on the other hand by means of sono- 

 rous vibrations, ought necessarily to contribute to the progress of light 

 itself, as well as to that of acoustics. 



