4 02 THE POPULAR SCIENCE MONTHLY. 



in appearance, although its immobility is not absolute. If the air be- 

 comes moist, it falls into deliquescence ; if too dry, into efflorescence. 

 It does not possess the same volume nor the same angles in summer 

 and in winter. Still, these changes are relatively slight, and if we 

 take our crystal from the drawer, in which it has been kept inert, and 

 put it in more favorable conditions, it will resume its development. 

 Heated too much, attacked by a strong enough chemical agent, or 

 subjected to any excessive influence, the body will be destroyed, 

 and will experience the more profound modification commonly called 

 death. 



May we not also say that there are diseases of minerals ? Can 

 we not recognize in some of them a tendency to a healing, or, in other 

 words, to a return toward the state of primitive equilibrium when 

 the cause of the evil has disappeared provided, always, that the 

 divergence from that position of equilibrium has not been too con- 

 siderable ? We may cite in illustration of this hypothesis the numer- 

 ous cases of mutilations of crystals that have been studied by Leblanc, 

 Beudant, Lavalle, De Senarmont, and M. Pasteur, on the bimalate of 

 ammonia ground up in polishing, nitrate of lead, sea-salt, hydrochlorate 

 of ammonia, or crystals of white potash alum, mutilated in certain lines, 

 which, immersed anew in a solution colored with chrome alum, have 

 their wounds cicatrized before resuming their interrupted develop- 

 ment a phenomenon which is made visible by the difference in color 

 of the two isomorphous salts. These curved, twisted, deformed, and 

 monstrous crystals, diverted from regularity by causes most usually 

 unknown, but of which science is on the way toward discovery, 

 would make, in regard to their malformations, objects of a mineral 

 teratology. 



The higher the stages of development which bodies reach, the 

 more their forms become complicated ; here, again, the chain seems to 

 be uninterrupted. I thought I had substantiated a tendency toward 

 perfection in the curious so-called mimetic appearances which plagio- 

 case feldspar, leucite, analcime, senarmentite, and many other minerals 

 exhibit, phenomena by which many crystals belonging to a more com- 

 plicated system group themselves in a determined number, so as to 

 offer the deceptive appearance of a single individual belonging to 

 a less complicated system. M. Pilo, on the other hand, sees in this 

 march toward a more simple form a retrogradation, an inverse phe- 

 nomenon of degeneracy, which he compares to atavism. I yield to 

 his view, and in doing this take notice of one other correlation be- 

 tween the two opposite extremities in the scale of beings. There is 

 also a passage of crystalline systems among themselves, and each 

 property effects this passage separately a displacement of optical axes 

 which, diminishing their angle, transforms a biaxial crystal to a uni- 

 axial one, successively for each of the colors of the spectrum ; an un- 

 equal thermic dilatation, positive or negative, following the three axes 



