OF ARTS AND SCIENCES : MAY 24, 1864. 311 



contain the two salts in very different proportions. And Bernhardi, 

 while agreeing with Haiiy that each substance can assume but one 

 primitive form, admitted that different substances may possess the same 

 primitive form ; and also, that a body may have the power to impress 

 upon another with which it is mingled its own peculiar crystalline 

 shape. Finally, in his theory of " vicai'ious constituents," — bodies 

 which are capable of replacing each other in combination without 

 thereby inducing a change of form, — Fuchs had made a near ap- 

 proach to the theory of Isomorphism. 



It remained for Mitscherlich, by collating and generalizing the views 

 of those who had gone before him, and by largely adding to the facts 

 which they had accumulated, to develop this law ; nor did he at first 

 perceive it in its true light. In his second memoir Mitscherlich says : 

 " Do different elements take the same crystalUne form when com- 

 bined with the same number of atoms of one, or of several other ele- 

 ments? Is identity of crystalline form dependent solely upon the 

 number of atoms ? Is it independent of the chemical nature of these 

 atoms ? Accident leading me at first to investigate a series of com- 

 pounds which answered all these questions in the affirmative, I was on 

 the point of regarding my results as a general law. But on extending 

 my researches to other combinations, ... I found that this identity 

 does not necessarily follow." And he was finally led to the view that 

 " certain elements, when united with the same number of atoms of one 

 or of several elements, assume the same crystalline form ; and that the 

 elements may in this respect be divided into groups." 



If to this be added the property of the elements in the several groups 

 to replace each other in varying proportions in a compound, without 

 materially changing its crystaUine form, we have the true expression of 

 the law of Isomorphism. 



The discovery of Isomorphism showed that the first axiom of Haiiy 

 was inexact, and required an essential modification ; the discovery of 

 Dimorphism, made at the same time, completely overturned Haiiy's 

 second axiom. It is a proof of the sagacity displayed by Mitscherlich 

 in these researches, that, in the long time which has elapsed since they 

 were made, his deductions have received no important alteration ; even 

 his own genius could in after life only add to the facts upon which the 

 conclusions arrived at in his youth were founded. The importance of 

 his results to chemistry and mineralogy was at once appreciated ; while 

 their very brilliancy has obscured his subsequent works. 



