278 
stones; then the remonstrance of the chemist was founded 
in truth and reason, ‘ 
It was the discovery of isomorphism that explained the 
anomalies and enigmas which thus in many cases seemed 
to justify the mineralogist in standing apart from the 
chemist, and preferring to discriminate, define, and classify 
minerals by appealing to superficial characteristics, rather 
than to the most fundamental feature_of such bodies, their 
chemical molecular structure. 
It came now to be seen that in the language of the 
earlier chemistry alumina and sesquioxide of iron, on the 
one hand, were able to represent the same ingredient in 
the garnet, while on the other hand, also, the lime, the 
magnesia, and the protoxide of iron might equally re- 
present one another in the silicate in question, provided 
that the chemical structure of the compound was not 
altered, that is to say, could be expressed by a general 
formula that was equally applicable to each variety of the 
mineral ; the identity of the crystallographic features of 
all those garnets being the evidence that the unity of the 
mineral type had not been overstepped by the inter- 
changes of the elements. The application of this great 
discovery left chemistry master of the situation, and 
relegated into the regions of darkness the systems of 
classification that were not built on chemical and crystal- 
lographic principles. It was Mitscherlich, aided as vom 
Rath tells us by the young Gustav Rose, who made this 
grand announcement to the world in the year 1823. 
The light which was thus shed on the dark and till then 
uncertain problems that might connect the crystalline 
form with chemical structure, gave, as it were, new life to 
the vigorous school that owed its chemical precision to 
the great Professor at Stockholm, the school to which the 
two Roses and Wohler belonged. The purely chemical 
problems of mineralogy received their constant attention ; 
and Gustave Rose, by publishing his crystallography, 
asserted the co-ordinate functions of the goniometer and 
the balance in the future discussions of all the larger 
questions of the mineralogist. 
He, in fact, unconsciously perhaps, was now initiating 
the method to which, with a fine unity of purpose, he 
adhered through his life. 
Thus, for instance, we find him in 1831-33 discussing 
the somewhat paradoxical resemblance in the crystallo- 
graphic constants of the minerals augite and hornblende, 
as suggested by Uralite, a mineral uniting the outline 
form of the one with the internal structure of the other ; 
in fact a pseudomorph of hornblende after the form of 
augite, 
Then in 1836 came his masterly memoir on the forms 
of Aragonite, the distinction of which from calcite had 
been established by Haiiy in the beginning of the 
century. Afterwards, among a mass of works, we find 
memoirs on the differences of crystallographic habit in 
Albite, and the nearly related variety of the same felspar 
pericline, a subject to which he returned in later times ; 
on the dimorphism of iridium, of palladium, and again of 
zinc ; several treating on the marvellous connection by 
which certain kinds of hemisymmetry in crystals are 
associated with the localisation on them of opposite 
electric conditions under changes of temperature (pyro- 
electricity), which he illustrated in the case of the tour- 
maline, and among his latest memoirs by a most masterly 
NATURE. 
one on pyrites and cobalt-glance. Quartz he made an 
object of especial study, explaining the character of its 
twin forms; and no memoirs in the whole range of 
crystallographic research, not excepting the splendid work 
in which Des-Cloiseaux capped, as it were, the labour of 
this great master on the crystallography of quartz. 
challenged the attention and been a sort of exercising- 
ground for several of the great mineralogists of Germany. 
in 1825, measured the first olivine crystal from the Pallas 
meteorite, and he, Haidinger, Breithaupt, and Wéhler, 
| Aug. 7, 1873 
Rose, can surpass, in originality and precision, that by 
Meteorites and the minerals which they contain have 
Berzelius, indeed, set the example, but it was Rose who, 
have all contributed invaluable material for the scientific 
history of these very difficult and interesting objects of 
investigation. And to G. Rose we owe the most pene- 
trating insight into their structure, and the best attempt 
thus far made at classifying them. So, too, the sum of 
his thought and labour on the classification of minerals 
was given in his “ crystallo-chemische mineral-system,” 
published twenty-one years ago, in which he, so to say, 
demolished, by leaving no further excuse for perpetuating, 
the system which was identified with the name of Mohs, 
or indeed any other system to which chemical law was 
not the master key. 
But one great work that Gustave Rose might have 
done, and better done perhaps than any living man, was 
the writing a treatise on Petrography. Mineralogy, the sci- 
ence of minerals, stands to petrography, the science that 
describes rocks and investigates their history, somewhat as 
biography stands to history itself, or as histology to physio- 
logy, The reason why a geologist is hardly ever a master of 
petrography is that he is so seldom, in England, at least, 
amineralogist. And itis precisely because Gustav Rose 
was, and Naumann is, a complete mineralogist and crys- — 
tallographer, and that both have profoundly studied the 
characters of the minerals in association which form rocks, 
that either of these two veteran professors might have 
written—alas ! a month ago we might have said may yet — 
write—such a treatise on rocks as probably no other living 
man could write. Gustav Rose began an admirable 
training in the field for such a study when, in the com- 
pany of A, von Humboldt and G, Ehrenberg, he traversed 
European Russia and found himself among the rocks 
of the Ourals in 1829. The results of this historical 
progress were given to the world in two volumes in 1837- 
1842, The memoirs which he published subsequently to 
this time and to his becoming full professor (he had been 
extraordinary professor since 1826) of mineralogy at 
Berlin, treat very frequently of rock minerals; and in- 
deed deal, in the majority of instances, with those more 
ordinary minerals which perform an important function 
as constituents of rocks; quartz, felspar, mica, horn- 
blende, augite, seem never to weary him in observation or 
exhaust his powers of telling some new fact regarding 
them. One of his latest papers on the very common 
mineral, mica, is one of the most admirable of his re- 
searches. It was published, like most of his memoirs, in 
Poggendorft’s Azalen, and treated on the interpenetration 
by one another, of various kinds of mica, and of these, 
with hematite and pennine. 
It would be unnecessary, for the purpose of this slight 
sketch of Gustav Rose’s labours, to go further into de- 
