408 Prof. Whewell on Isomorphism^ 



discover the proper formula. This labour has, as yet, been 

 executed for a few minerals only ; so that there remains still 

 abundant occupation of this kind for the mineralogist, and it 

 can hai'dly be doubted, that a clearer insight into the constitu- 

 tion of crystalline substances will reward such researches, if 

 diligently pursued. But the above instances, in which, in mi- 

 nerals of the most complex and apparently confused analysis, 

 order has been detected by the application of the doctrine of 

 isomorphism, appear to be sufficient to assure us that that 

 doctrine has a foundation in nature. 



If there be any instances in which the analyses do not con- 

 form to the formula proposed, as Mr. Brooke asserts to be 

 the case with regard to amphibole compared with Beudant's 

 formulae, there can be no doubt that we must allow either that 

 the formula is wrong, or the mineral wrongly named, wrongly 

 analysed, or impure. The isomorphous view of the constitu- 

 tion of bodies has not, nor can it have, any authority beyond 

 what it derives from its agreement with facts. The superiority 

 of this view over that of accidental mixture, arises from its 

 appearing that the latter gives no approximation at all to 

 many of the analyses; while the former has given, in the cases 

 which have been most carefully examined, a very close agree- 

 ment, under very trying circumstances. 



III. On the Principles of the Doctrine of Isomorphism. 



Besides Mr. Brooke's objections to the doctrine of isomor- 

 phism as not supported by sufficient evidence, he has put for- 

 ward several objections founded upon theoretical views, which 

 I shall very briefly touch upon. 



In p. 164, he says: " If soda and lime ai-e isomorphous in 

 relation to 1 or 2 or 3 atoms of silex, there is no obvious 

 reason why all the other elements that are deemed isomor- 

 phous in relation to 1 atom should not be so equally in rela- 

 tion to 2 or 3 atoms," &c. Mr. Brooke here and in other 

 cases appears to assume, that if any two elements x and y be 

 isomorphous in one case, they must be so in all: and this be- 

 cause there is no obvioics reason why it should be otherwise. 

 I confess this appears to me a hazardous mode of reasoning 

 in such matters. Whether the fact is so or not, must be de- 

 termined by analyses, and perhaps is hardly yet decided. 

 The elements which I have denoted by C, M, Fe, Mn, which 

 appear to be isomorphous in siliceous minerals, are, it would 

 seem, Tplesiomorphous when combined with carbonic acid. 



We must, I conceive, hold such ingredients in each mineral 

 species to be isomorphous, as appear, from analyses, to replace 



each 



