1829 .] 
Thoughts on Mineralogical Systems. 
257 
tion stone of the building, and to erect a system without attending to this essential 
part of the fabric is to build upon sand ; yet, with the exception of Mohs, this has 
keen the mistake of every mineralogist. Hauy, however, had the good sense to per- 
ceive that there are two distinct objects to be attained, and the merit of indicating 
clearly the nature and objects of each ; nor did he claim for his own more merit than 
was due ; for he expressly calls it a method of classification and not of discrimina- 
tion (Disc. Prel. page xv.) 
5. We are now then to inquire, what are those characters or properties which 
may be advantageously applied to the discrimination and recognition of minerals to 
this end. It is sufficient to consider what is the object to be attained. This is the 
certain recognition of the species, and by signs the value of which is easily and 
promptly determinable. It results, then, that the more definite a character be, the 
more valuable it will be. In particular, if any character can be found which is ex- 
pressible in figures, it will bring to the solution of the question that precision which 
is always obtainable as soon as a subject of inquiry is brought under their domi- 
nion. 
6. We have two characters of this description, specific gravity and hardness. 
The first expresses the number of volumes of water equal in weight to a given vo- 
lume of the mineral, and we may suppose a priori that this number would be pretty 
uniformly the same when determined for the same mineral species ; and in fact, such 
is the case, or at least the variation is within such small limits as to leave the cha- 
racter all necessary precision. The hardness is expressed in figures which indicate 
the place of a mineral in the whole series, arranged according to their relative hard, 
ness. This character, though equally susceptible of precision as the former, has not 
had that attention paid to it as yet to render its employment sufficiently satisfactory'; 
nevertheless, even with the limited scale as yet determined, it will be found a cha- 
racter of very great value. 
7. VVe may, in considering what has just been stated, judge how great was Wer- 
ner’s error in rejecting the aid of numerical determination in the case of the only 
two characters, generally applicable, which are susceptible of it. By employing such 
vague terms as heavy, rather heavy, rather light, light, See. hard, very hard, not par- 
ticularly hard, he broke down the only barriers erected by nature to separate the 
species ; and thus rendered the science of mineralogy a confused mass of gradations 
or transitions, in which nothing appeared certain except the resemblances. He in 
fact shut the door of knowledge to bis scholars, who were thus restricted to the ac- 
quisition of an empirical tact, by which, if they had sufficient practice and a good 
memory, they could recognise any mineral which happened to be like those they bad 
before seen, but if otherwise they could determine nothing. Nor did their deter- 
mination, even in the case of those they had seen and known, ever approach the cer- 
tainty required in scientific determinations. It was at best a mere guess, and might 
or might not be right or wrong as their memory served or failed them. 
8. "There is another character which is equally susceptible of the application of geo- 
metrical considerations, and which therefore, with the addition of the other two, 
would introduce great precision into the determination of the species, were it univer- 
sally applicable. This is crystalline form, which however, unfortunately, is only 
found in a limited number of each species, and these the most rarely met with. It 
is therefore useless for those (the greater number) which possess no regular form ; 
Useless, I mean, as a principle on which to found an analytical arrangement, though, 
as forming a very interesting part of the history of every mineral, it is a branch of 
the science not to be undervalued. Indeed it is in the study of the crystalline rela- 
tions of minerals that the student will meet with some of the brightest generalisa- 
tions in the whole compass of the science. 
9. Similar remarks may apply to one other, and the only other character which 
admitsof equally precise determination; I mean the refractive power of the substance, 
which, were it universally determinable, would form a character of great value. But 
to enable the observer to determine the refractive power of a mineral, it must be in 
some degree transparent, a circumstance not true of one mineral in three. We are 
compelled, then, equally to reject this as a fundamental character in our attempt at 
an analytical arrangement of minerals, although, like the preceding, it may be often 
used for the illustration of the species. 
10. Connected with this character, and in some measure susceptible of the preci- 
sion which figures give, is the property of polarisation. The number and position 
of the axes of a crystal is known to depend, or rather be connected with the sys- 
tem of crystallisation to which it belongs ; and if we could, in the case of crystalline 
figure being indefinite or effaced altogether, determine the number and position of 
