M. Pasteui' on Aspartic and Malic Acids. 283 



principle of isomorphism has not only benefited chemistry, but 

 mineralogjr has also received a fresh impulse from this discoveiy ; 

 for it then became possible in that science to form a conception 

 of, and define by precise formulae, the abstract types of many 

 mineral species which scarcely ever occur naturally in a state of 

 purity, because they are constantly met with mixed with sub- 

 stances isomorphous with their principal elements, which can 

 and, indeed, must necessarily, exist with them in propor- 

 tions more or less abundant when the combination took place. 

 Thus, in an analogous case, geometricians have a perfect idea of 

 a circle, although neither nature nor art ever presents such a 

 thing as an absolutely perfect circle. 



In proportion as the science of chemistry advances in the 

 investigation of the intimate constitution of bodies, wherein 

 lies its future development, it cannot do other than gain by con- 

 tact with those sciences which study the same objects under a 

 different point of \dew, and by processes differing from those 

 employed by it. Two sciences especially, crystallography and 

 optics, appear to be destined to be henceforth its auxiliaries, 

 which are not merely useful, but absolutely indispensable, in order 

 to support and legitimize the theories which are suggested by 

 the results of chemical investigation. It is however true that the 

 foiTner will not furnish any characteristics which can be applied 

 directly to the corpuscles between which chemical actions take 

 place. According to all appearance, the minute solids of similar 

 nature, by the aggregation of which every crystal of sensible 

 dimensions is formed, are numerous assemblages of those corpus- 

 cles, which, by their reciprocal attractions, are grouped together 

 among each other according to a certain mode of relative arrange- 

 ment in the physical conditions in which they may be placed. 

 The crystalline form which is observed in the mass would there- 

 fore be a joint consequence of those attractions, and the circum- 

 stances which modify them. Thus, by varying these circum- 

 stances, and following with attention the peculiarities which 

 under their divers influences present themselves both in the 

 whole and the details of form, indications will be discovered 

 which will have a connexion more or less intimate with the 

 attractive forces exercised by the chemical corpuscles, the as- 

 semblage of which constitutes the embryo crystal. These ge- 

 neral studies might be considerably facilitated and rendered 

 more positive by the observation of the power of rotation of 

 polarized light, which in the numerous instances in which it 

 exists makes us acquainted with specific properties inherent in 

 the chemical corpuscles themselves, not only after the trials 

 which may have caused some modification in them, but by the 

 mere observation of the sensible effects which arc produced upon 



