186 
NATLORE 
[ Dec. 16, 1869 
It is a most valuable principle in physical science, never 
to be lost sight of, that we must not seek to explain by the 
assumption of new species of force or action any phenomena 
which have not been recognised to be inexplicable by means 
of properties of matter or motion already proved to exist. 
Before leaving this subject I must refer to the extraordinary 
fact, lately ascertained, that the spectrum of the head of 
one of the smaller comets is that of incandescent vapour 
of carbon, of a substance which, with the most tremendous 
heat attainable in our laboratories, we cannot even melt, 
much less reduce to vapour: so that to find its spectrum 
we are obliged to employ it as it exists in olefiant gas or 
other combined form. But it is premature to speculate 
further on such incomplete data as we yet possess with 
respect to the spectroscopic appearances of comets. It is 
not rash to venture the prediction that the very first ap- 
plication of the spectroscope to a really fine comet will 
give us at least as much additional insight into the nature 
of these bodies as the total eclipse of 1868 gave with 
regard to the atmosphere of the sun. P. G. TAIT 
DANA’S MINERALOGY 
A System of Mineralogy: Descriptive Mineralogy com- 
prising the most Recent Discoveries. By James 
Dwight Dana, Silliman Professor of Geology and 
Mineralogy in Yale College, etc., aided by George 
Jarvis Brush, Professor of Mineralogy and Metal- 
lurgy in the Sheffield Scientific School of Yale Col- 
lege. Fifth edition, 8vo. pp. 827, figures 617. (London: 
(Triibner & Co.) 
Il. 
poe in the subdivisions of the silicates, Professor 
Dana has adhered pretty nearly to the classification 
adopted in his fourth edition ; which accords also in its 
general features, though not in its details, with that on 
which the minerals in the British Museum are arranged. 
The arrangement of the silicates in his new edition is a 
step that must be called tentative towards a simpler and 
more philosophical classification of these numerous and 
important salts. We certainly feel some hesitation in 
adopting either the terminology or the divisions Professor 
Dana introduces. The terms bi- and uni-silicate are not 
happy for the expression of oxygen ratios ; not so happy, 
for instance, as the term singulo-silicate used for the latter 
by Rammelsberg, or the ortho-silicates of Odling. We own 
to a partiality for the view of Dr. Odling regarding the 
different classes of silicates, on the ground partly of the 
harmonious relations he introduces between these and 
other multibasic salts, and also from the satisfactory way 
in which these very important minerals group themselves 
as ortho-, para-, or meta-silicates. We may take another 
occasion for illustrating this, and pass on to Professor 
Dana’s new and scholarlike handling of the whole ques- 
tion of nomenclature. 
Our author has shirked no labour or odium in the way 
he has faced this question. That trivial names are abso- 
lutely necessary in mineralogy no one who has dealt with 
the subject at all philosophically will question, Even 
such semi-trivial terms as ferrous aluminic garnet, calcio- 
ferric or magnesio-aluminic garnet, are almost too long 
for use ; but how should the composition of these bodies 
be described by names purely chemical ? 
Generally, therefore, we feel bound to acquiesce in the 
use of a trivial name for each mineral, and to subscribe 
to the rules Professor Dana has laid down for such names. 
These may be stated as the use of the termination -z¢e, 
except in names that have a hold on literature or use ; 
some care in adhering to proper etymological principles 
in derivative names ; and, finally, the law of priority of 
claim accorded in general, but with proper exceptions, 
to the first describer of a mineral. In applying these 
rules, Dana retains, so far as wec an enumerate them, 
some thirty-four names not ending in-z¢e,and changes about 
forty-seven of the names more or less generally received. 
We cannot, however, concur in the Professor’s criticism 
in his derivation of the spellings in all cases from the 
pseudo-Latin names given to metals by the chemist. 
Thus, to call nickeline “niccolite” and not “‘nickelite” is to 
lose sight of an essential part of the original form of a 
word of which, in fact, our familiar term “ Old Nick” is 
the English shape. Surely, too, bismuth ochre should 
become not bismite, but bismuthite. Nor can we agree 
with the dismissal by Dana of the term hemimorphite, 
which was given to the monohydrated dizincous silicate 
by Kenngott. Our author reverts to the old name of 
calamine, between the use of which and of smithsonite, 
as names sometimes attached to the zinc carbonate, some- 
times to the silicate, there has long existed a confusion 
that is best ended by the adoption of at least one new 
name, And Kenngott’stermhad at any rate this great merit, 
that it seized a characteristic of the crystallised silicate, 
by virtue of which it stands conspicuous among almost 
all other minerals, and certainly is distinguished from the 
other calamine, the character, namely, of being truly 
hemimorphous ; that is to say, of presenting a given cry-_ 
stalline form all the planes that should occur on one side 
of a plane of symmetry, and none of the planes of that 
form that would, if the crystal were holosymmetrical, be 
met with on the other side of that plane of symmetry. 
We plead, therefore, strongly in behalf of Kenngott’s 
name. As regards the merging of the term hornblende 
in that of amphibole as carried out by Dana, we 
would prefer to see the whole nomenclature of these 
augitic and hornblendic minerals so handled that we 
might have a general term for all the groups of minerals 
united under a common chemical type; and separate 
terms, still generic, that might embrace the minerals, 
whether of prismatic, oblique, or anorthic type, that present 
the kind of homeomorphism that demarks these groups. 
The trivial names for the different species or varieties — 
under each group would remain nearly as they are. Now 
Professor Dana selects the term amphibole for the most 
general of these expressions, and he includes under a 
pyroxene sub-group enstatite (prismatic), wollastonite 
(oblique), and what he further calls pyroxene (oblique 
but homceomorphous with enstatite) ; and then after a 
spodumene sub-group he introduces an amphibole sub- 
group. We venture to think that the term “amphibolic 
minerals” used for the whole might well be made to 
embrace: Firstly, an augitic group, including as its 
members, (@) enstatite, with hypersthenic minerals, (4) 
diopside, with sahlite, hedenbergite, and the fassaite 
(aluminous varieties, (c) spodumene and petalite, (@) ach- 
mite, (e) rhodonite and babingtonite ; Secondly, a horn- 
blendic group, embracing as its subdivisions, (@) kupfferite 
with anthophyllite, (4) tremolite, with actinolite, griinerite 
