394 



NA rURE 



[Fed. 24, 1887 



undeveloped, and its very notation undefined. Its culti- 

 vators, absorbed in the Sisyphean task of establishing new 

 species and \arieties, too often treat their science, with all 

 its glorious possibilities, as though it were but akin to 

 postage-stamp lore ! 



How is it, we may profitably ask, that the biological 

 sciences have made such prodigious advances, while the 

 mineralogical ones have lagged so far behind ? We must 

 ascribe the result, 1 believe, to two causes : — 



In the first place, improvements in the construction of 

 the laicroscope, and more especially the perfecting of 

 methods of study by means of thin sections, have im- 

 measurably enlarged the biologist's field of observation ; 

 histology and the cell-theory, embryology with all its 

 suggestiveness, and many important branches of physio- 

 logical research, must have languished, if, indeed, they 

 could ever have seen the light, but for aid afforded by the 

 microscopical methods of inquiry. 



In the second place, the growth of geological and 

 palaeontological knowledge has been the leading factor 

 in that profound revolution in biological ideas which, 

 sweeping before it the superstition of fixity of species, has 

 endowed this branch of natural science with the trans- 

 forming conception of evolution. 



Now these two causes, which have done so much for 

 biology, are already working out the regeneration of 

 mineralogy ; and I doubt not that the fruits brought forth 

 by the latter science will be equally satisfactory with those 

 of the former. 



The application of the microscope to the study of 

 minerals has proved less easy than in the case of animal 

 and vegetable structures. More than a century ago, it is 

 true, several French geologists employed the method of 

 crushing a rock, and of picking out from its powder the 

 several minerals of which it was composed, for micro- 

 scopic study; and in 1S16, Cordier endeavoured, by 

 systematising the methods followed by his predecessors, 

 Daubenton, Dolomieu, Fleurian, and others, to elaborate 

 a scheme for the mineralogical analysis of rocks by the 

 aid of the microscope. In recent years the French geo- 

 logists, with MM. Fouquc and Michel Levy at their head, 

 have shown how, by the employmerit of the electro-magnet, 

 of fluids of high density, and of various chemical reagents, 

 this work of isolating the several minerals of a rock for 

 microscopic study or chemical analysis may be greatly 

 facilitated. 



But the great drawback to this method of microscopic 

 study of rocks, as devised in France, was found in the 

 circumstance that it began by destroying the rock as a 

 whole, and hopelessly obliterating the relations of its 

 mineralogical constituents. Delesse and other observers, 

 it is true, succeeded in obviating this difficulty, to some 

 e.xtent, by studying the structure of rocks as seen in 

 polished surfaces under the microscope by reflected 

 light. 



The greatest step in advance in connection with the 

 microscopic study of rocks was undoubtedly made, how- 

 ever, when it was shown that transparent sections of 

 minerals, rocks, and fossils can be prepared, comparable 

 to those so constantly employed by biologists in their 

 researches. William Nicol, of Edinburgh, was the first 

 to disco\er, in the year 1827, how the mechanical diffi- 

 culties in the way of the preparation of such sections could 

 best be surmounted ; while Mr. Sorby, in a memorable 

 communication to this Society, in 1S58, showed us the 

 first-fruits of the wonderful harvest of results to be ob- 

 tained by the employment of this method. 



But if the birthplace of the one method of microscopic 

 study of rocks was France, and of the other Britain, it 

 must be confessed that a large part of the merit of de- 

 veloping and improving these methods of inquiry is due 

 to the Germans. To the labours of the numerous, patient, 

 and accurate students in that country must be ascribed 

 much of the perfection to which the methods of microscopic 



mineralogy have now attained ; though we must not for- 

 get in this connection many most valuable contributions 

 to the study from Scandinavia, Holland, Italy, and the 

 United States. 



As in the case of biology the results attained by the 

 geologist have been the means of awakening new interests 

 and inspiring a new philosophy, so in the case of miner- 

 alogy other problems have been suggested, and entirely 

 fresh conceptions of the scope of the science have followed 

 from the development of geological thought. We are 

 thus led to regard minerals, not simply as a set of curious 

 illustrations of mathematical and chemical laws, but as 

 important factors in the evolution of the globe. Mineral 

 collections in the past have resembled greenhouses, 

 wherein only beautiful, though often abnormal growths 

 are admitted ; but in the future they will be like the 

 herbaria of the botanist, where mere beauties of form 

 and colouring are subordinated to the illustration of 

 natural relationships and to the elucidation of the great 

 problems of origin and development. Far be it from me 

 to undervalue those wonderful crystals, the choice flowers ij 



of the mineral kingdom, which adorn our museums ; but 

 as there are many plants of extreme scientific interest 

 which happen to possess only inconspicuous flowers, so 

 there are not a few microscopic minerals, the study of 

 which may lead us to the recognition of some of the most 

 important laws of the mineral world. 



I believe that what geology has already done for biology 

 she is now accomplishing for mineralogy ; it may, indeed, 

 be instructive to point out how, in every one of its depart- 

 ments, the employment of microscopic methods and the 

 suggestion of new lines of thought is causing mineralogy 

 to develop in just the same directions as biology has 

 already taken before her. In this way we may perhaps 

 best convince ourselves that mineralogy is once more 

 asserting her position in the family of the natural 

 sciences. 



Every natural-history science presents us with four 

 distinct classes of problems. With respect to the objects 

 of our study, we may make inquiries concerning their 

 forms, their actions, their relations, and their origin. The 

 answers to the first class of questions constitute Morpho- 

 logy, to the second Physiology, to the third Chorology or 

 Distribution, and to the fourth .-Etiology. The great 

 problems of the mineral world, as I shall proceed to show, 

 fall under precisely the same categories ; and we may 

 perhaps gather some useful hints by a comparison be- 

 tween the immature results of the mineralogist in each of 

 these departments and those more perfect ones which 

 have been attained by the botanist and zoologist. 



The morphology of minerals was for along time studied 

 to the exclusion of all other branches of the science ; 

 for the problems connected w'th form and structure were 

 those which naturally first attracted the students of the 

 " inorganic " world. 



Few generalisations of science are so beautiful, and at 

 at the same time so suggestive, as those which have been 

 arrived at by a discussion of the accurate measurements 

 of crystal-angles. The constancy, within certain narrow 

 limits, of corresponding angles, amid the almost infinite 

 diversity of form assumed by crystals of the same mineral, 

 is not less striking than the simplicity of the mathematical 

 laws by which all these varied forms can be shown to be 

 related to one another. 



But the study of the morphology of minerals, which can- 

 not be carried beyond a certain point by the aid of the 

 goniometer, is capable of being pushed infinitely farther 

 when we investigate the internal structure of their crystals, 

 as illustrated by their optical and other physical pro- 

 perties. Not only do we find the minutest details of 

 their external form to be correlated with peculiarities of 

 molecular structure, as revealed by their action on a beam 

 of polarised light, but delicate diflerences in internal 



