already said, an imperfect representative of the department of human
knowledge to which it belongs. The attempts at the science have
generally been made by collecting various kinds of information
respecting mineral bodies; but the science which we require is a
complete and consistent classified system of all inorganic bodies.
For chemistry proceeds upon the principle that the constitution of a
body invariably determines its properties; and, consequently, its
kind: but we cannot apply this principle, except we can speak with
precision of the _kind_ of a body, as well as of its composition. We
cannot attach any sense to the assertion, that "soda or baryta has a
metal for its base," except we know what _a metal_ is, or at least
what properties it implies. It may not be, indeed it is not,
possible, to define the kinds of bodies by words only; but the
classification must proceed by some constant and generally
applicable process; and the knowledge which has reference to the
classification will be precise as far as this process is precise,
and vague as far as this is vague.
There must be, then, as a necessary supplement to Chemistry, a
Science of those properties of bodies by which we divide them into
_kinds_. Mineralogy is the branch of knowledge which has discharged
the office of such a science, so far as it has been discharged; and,
indeed, Mineralogy has been gradually approaching to a clear
consciousness of her real place, and of her whole task; I shall give
the history of some of the advances which have thus been made. They
are, principally, {315} the establishment and use of External
Characters, especially of _Crystalline Form_, as a fixed character
of definite substances; and the attempts to bring into view the
connexion of Chemical Constitution and External Properties, made in
the shape of mineralogical _Systems_; both those in which _chemical
methods of arrangement_ are adopted, and those which profess to
classify by the _natural-history method_.
{{316}}
CRYSTALLOGRAPHY.
CHAPTER I.
PRELUDE TO THE EPOCH OF DE LISLE AND HAÜY.
OF all the physical properties of bodies, there is none so fixed,
and in every way so remarkable, as this;--that the same chemical
compound always assumes, with the utmost precision, the same
geometrical form. This identity, however, is not immediately
obvious; it is often obscured by various mixtures and imperfections
in the substance; and even when it is complete, it is not
immediately recognized by a common eye, since it consists, not in
the equality of the sides or faces of the figures, but in the
equality of their angles. Hence it is not surprising that the
constancy of form was not detected by the early observers. Pliny
says,[1\15] "Why crystal is generated in a hexagonal form, it is
difficult to assign a reason; and the more so, since, while its
faces are smoother than any art can make them, the pyramidal points
are _not all of the same kind_." The quartz crystals of the Alps, to
which he refers, are, in some specimens, very regular, while in
others, one side of the pyramid becomes much the largest; yet the
angles remain constantly the same. But when the whole shape varied
so much, the angles also seemed to vary. Thus Conrad Gessner, a very
learned naturalist, who, in 1564, published at Zurich his work, _De
rerum Fossilium, Lapidum et Gemmarum maxime, Figuris_, says,[2\15]
"One crystal differs from another in its angles, and consequently in
its figure." And Cæsalpinus, who, as we shall find, did so much in
establishing fixed characters in botany, was led by some of his
general views to disbelieve the fixity of the form of crystals. In
his work _De Metallicis_, published at Nuremberg in 1602, he
says,[3\15] "To ascribe to inanimate bodies a definite form, does
not appear consentaneous to reason; for it is the office of
organization to produce a definite form;" {317} an opinion very
natural in one who had been immersed in the study of the general
analogies of the forms of plants. But though this is excusable in
Cæsalpinus, the rejection of this definiteness of form a hundred
years later, when its existence had been proved, and its laws
developed by numerous observers, cannot be ascribed to anything but
strong prejudice; yet this was the course taken by no less a person
than Buffon. "The form of crystallization," says he,[4\15] "is _not
a constant character_, but is more equivocal and more variable than
any other of the characters by which minerals are to be
distinguished." And accordingly, he makes no use of this most
important feature in his history of minerals. This strange
perverseness may perhaps be ascribed to the dislike which Buffon is
said to have entertained for Linnæus, who had made crystalline form
a leading character of minerals.
[Note 1\15: _Nat. Hist._ xxvii. 2.]
[Note 2\15: p. 25.]
[Note 3\15: p. 97.]
[Note 4\15: _Hist. des Min._ p. 343.]
It is not necessary to mark all the minute steps by which
mineralogists were gradually led to see clearly the nature and laws
of the fixity of crystalline forms. These forms were at first
noticed in that substance which is peculiarly called rock-crystal or
quartz; and afterwards in various stones and gems, in salts obtained
from various solutions, and in snow. But those who observed the
remarkable regular figures which these substances assume, were at
first impelled onwards in their speculations by the natural tendency
of the human mind to generalize and guess, rather than to examine
and measure. They attempted to snatch at once the general laws of
geometrical regularity of these occurrences, or to connect them with
some doctrine concerning formative causes. Thus Kepler,[5\15] in his
_Harmonics of the World_, asserts a "_formatrix facultas_, which has
its seat in the entrails of the earth, and, after the manner of a
pregnant woman, expresses the five regular geometrical solids in the
forms of gems." But Philosophers, in the course of time, came to
build more upon observation, and less upon abstract reasonings.
Nicolas Steno, a Dane, published, in 1669, a dissertation _De Solido
intra Solidum Naturaliter contento_, in which he says,[6\15] that
though the sides of the hexagonal crystal may vary, _the angles are
not changed_. And Dominic Gulielmini, in a _Dissertation on Salts_,
published in 1707, says,[7\15] in a true inductive spirit, "Nature
does not employ all figures, but only certain ones of those which
are possible; and of these, the determination is not to be fetched
from the brain, or proved _à priori_, but obtained by experiments
and observations." And {318} he speaks[8\15] with entire decision on
this subject: "Nevertheless since there is here a principle of
crystallization, the inclination of the planes and of the angles is
always constant." He even anticipates, very nearly, the views of
later crystallographers as to the mode in which crystals are formed
from elementary molecules. From this time, many persons labored and
speculated on this subject; as Cappeller, whose _Prodromus
Crystallographiæ_ appeared at Lucern in 1723; Bourguet, who
published _Lettres Philosophiques sur la Formation de Sels et de
Cristaux_, at Amsterdam, in 1792; and Henckel, the "Physicus" of the
Elector of Saxony, whose _Pyritologia_ came forth in 1725. In this
last work we have an example of the description of the various forms
of special classes of minerals, (iron pyrites, copper pyrites, and
arsenic pyrites;) and an example of the enthusiasm which this
apparently dry and laborious study can excite: "Neither tongue nor
stone," he exclaims,[9\15] "can express the satisfaction which I
received on setting eyes upon this sinter covered with galena; and
thus it constantly happens, that one must have more pleasure in what
seems worthless rubbish, than in the purest and most precious ores,
if we know aught of minerals."
[Note 5\15: Linz. 1619, p. 161.]
[Note 6\15: p. 69.]
[Note 7\15: p. 19.]
[Note 8\15: p. 83.]
[Note 9\15: p. 343.]
Still, however, Henckel[10\15] disclaims the intention of arranging
minerals according to their mathematical forms; and this, which may
be considered as the first decided step in the formation of
crystallographic mineralogy, appears to have been first attempted by
Linnæus. In this attempt, however, he was by no means happy; nor
does he himself appear to have been satisfied. He begins his preface
by saying, "Lithology is not what I plume myself upon." (_Lithologia
mihi cristas non eriget_.) Though his sagacity, as a natural
historian, led him to see that crystalline form was one of the most
definite, and therefore most important, characters of minerals, he
failed in profiting by this thought, because, in applying it, he did
not employ the light of geometry, but was regulated by what appeared
to him resemblances, arbitrarily selected, and often
delusive.[11\15] Thus he derived the form of pyrites from that of
vitriol;[12\15] and brought together alum and diamond on account of
their common octohedral form. But he had the great merit of
animating to this study one to whom, more perhaps than to any other
person, it owes its subsequent progress; I mean Romé de Lisle.
"Instructed," this writer says, in his preface to his _Essais de
Crystallographie_, "by the works of the celebrated Von Linnée, how
{319} greatly the study of the angular form of crystals might become
interesting, and fitted to extend the sphere of our mineralogical
knowledge, I have followed them in all their metamorphoses with the
most scrupulous attention." The views of Linnæus, as to the
importance of this character, had indeed been adopted by several
others; as John Hill, the King's gardener at Kew, who, in 1777,
published his _Spathogenesia_; and Grignon, who, in 1775, says,
"These crystallizations may give the means of finding a new theory
of the generation of crystalline gems."
[Note 10\15: p. 167.]
[Note 11\15: Marx. _Gesch._ p. 97.]
[Note 12\15: _Syst. Nat._ vi. p. 220.]
The circumstance which threw so much difficulty in the way of those
who tried to follow out his thought was, that in consequence of the
apparent irregularity of crystals, arising from the extension or
contraction of particular sides of the figure, each kind of
substance may really appear under many different forms, connected
with each other by certain geometrical relations. These may be
conceived by considering a certain fundamental form to be cut into
new forms in particular ways. Thus if we take a cube, and cut off
all the eight corners, till the original faces disappear, we make it
an octohedron; and if we stop short of this, we have a figure of
fourteen faces, which has been called a _cubo-octohedron_. The first
person who appears distinctly to have conceived this _truncation_ of
angles and edges, and to have introduced the word, is
Démeste;[13\15] although Wallerius[14\15] had already said, in
speaking of the various crystalline forms of calcspar, "I conceive
it would be better not to attend to all differences, lest we be
overwhelmed by the number." And Werner, in his celebrated work _On
the External Characters of Minerals_,[15\15] had formally spoken of
_truncation_, _acuation_, and _acumination_, or replacement by a
plane, an edge, a point respectively, (_abstumpfung_, _zuschärfung_,
_zuspitzung_,) as ways in which the forms of crystals are modified
and often disguised. He applied this process in particular to show
the connexion of the various forms which are related to the cube.
But still the extension of the process to the whole range of minerals
and other crystalline bodies, was due to Romé de Lisle. {320}
[Note 13\15: _Lettres_, 1779, i. 48.]
[Note 14\15: _Systema Mineralogicum_, 1772-5, i. 143.]
[Note 15\15: Leipzig, 1774.]
CHAPTER II.
EPOCH OF ROMÉ DE LISLE AND HAÜY.--ESTABLISHMENT OF THE FIXITY OF
CRYSTALLINE ANGLES, AND THE SIMPLICITY OF THE LAWS OF DERIVATION.
WE have already seen that, before 1780, several mineralogists had
recognized the constancy of the angles of crystals, and had seen (as
Démeste and Werner,) that the forms were subject to modifications of
a definite kind. But neither of these two thoughts was so
apprehended and so developed, as to supersede the occasion for a
discoverer who should put forward these principles as what they
really were, the materials of a new and complete science. The merit
of this step belongs jointly to Romé de Lisle and to Haüy. The
former of these two men had already, in 1772, published an _Essai de
Crystallographie_, in which he had described a number of crystals.
But in this work his views are still rude and vague; he does not
establish any connected sequence of transitions in each kind of
substance, and lays little or no stress on the angles. But in 1783,
his ideas[16\15] had reached a maturity which, by comparison,
excites our admiration. In this he asserts, in the most distinct
manner, the _invariability_ of the angles of crystals of each kind,
under all the changes of relative dimension which the faces may
undergo;[17\15] and he points out that this invariability applies
only to the _primitive forms_, from each of which many secondary
forms are derived by various changes.[18\15] Thus we cannot deny him
the merit of having taken steady hold on both the handles of this
discovery, though something still remained for another to do. Romé
pursues his general ideas into detail with great labor and skill. He
gives drawings of more than five hundred regular forms (in his first
work he had inserted only one hundred and ten; Linnæus only knew
forty); and assigns them to their proper substances; for instance,
thirty to calcspar, and sixteen to felspar. He also invented and
used a goniometer. We cannot doubt that he would have been {321}
looked upon as a great discoverer, if his fame had not been dimmed
by the more brilliant success of his contemporary Haüy.
[Note 16\15: _Cristallographie, ou Description de Formes propres à
tous les Corps du Règne Minéral._ 3 vols. and 1 vol. of plates.]
[Note 17\15: p. 68.]
[Note 18\15: p. 73.]
Réné-Just Haüy is rightly looked upon as the founder of the modern
school of crystallography; for all those who have, since him,
pursued the study with success, have taken his views for their
basis. Besides publishing a system of crystallography and of
mineralogy, far more complete than any which had yet appeared, the
peculiar steps in the advance which belong to him are, the discovery
of the importance of _cleavage_, and the consequent expression of
the laws of derivation of secondary from primary forms, by means of
the _decrements_ of the successive layers of _integrant molecules_.
The latter of these discoveries had already been, in some measure,
anticipated by Bergman, who had, in 1773, conceived a hexagonal
prism to be built up by the juxtaposition of solid rhombs on the
planes of a rhombic nucleus.[19\15] It is not clear[20\15] whether
Haüy was acquainted with Bergman's Memoir, at the time when the
cleavage of a hexagonal prism of calcspar, accidentally obtained,
led him to the same conception of its structure. But however this
might be, he had the indisputable credit of following out this
conception with all the vigor of originality, and with the most
laborious and persevering earnestness; indeed he made it the
business of his life. The hypothesis of a solid, built up of small
solids, had this peculiar advantage in reference to crystallography;
it rendered a reason of this curious fact;--that a certain series of
forms occur in crystals of the same kind, while other forms,
apparently intermediate between those which actually occur, are
rigorously excluded. The doctrine of decrements explained this; for
by placing a number of regularly-decreasing rows of equal solids,
as, for instance, of bricks, upon one another, we might form a
regular equal-sided triangle, as the gable of a house; and if the
breadth of the gable were one hundred bricks, the height of the
triangle might be one hundred, or fifty, or twenty-five; but it
would be found that if the height were an intermediate number, as
fifty-seven, or forty-three, the edge of the wall would become
irregular; and such irregularity is assumed to be inadmissible in
the regular structure of crystals. Thus this mode of conceiving
crystals allows of certain definite secondary forms, and no others.
[Note 19\15: _De Formis Crystallorum._ Nov. Act. Reg. Soc. Sc. Ups.
1773.]
[Note 20\15: _Traité de Minér._ 1822, i. 15.]
The mathematical deduction of the dimensions and proportions {322}
of these secondary forms;--the invention of a notation to express
them;--the examination of the whole mineral kingdom in accordance
with these views;--the production of a work[21\15] in which they are
explained with singular clearness and vivacity;--are services by
which Haüy richly earned the admiration which has been bestowed upon
him. The wonderful copiousness and variety of the forms and laws to
which he was led, thoroughly exercised and nourished the spirit of
deduction and calculation which his discoveries excited in him. The
reader may form some conception of the extent of his labors, by
being told--that the mere geometrical propositions which he found it
necessary to premise to his special descriptions, occupy a volume
and a half of his work;--that his diagrams are nearly a thousand in
number;--that in one single substance (calcspar) he has described
forty-seven varieties of form;--and that he has described one kind
of crystal (called by him _fer sulfuré parallélique_) which has one
hundred and thirty-four faces.
[Note 21\15: _Traité de Minéralogie_, 1801, 5 vols.]
In the course of a long life, he examined, with considerable care,
all the forms he could procure of all kinds of mineral; and the
interpretation which he gave of the laws of those forms was, in many
cases, fixed, by means of a name applied to the mineral in which the
form occurred; thus, he introduced such names as _équiaxe_,
_métastatique_, _unibinaire_, _perihexahèdre_, _bisalterne_, and
others. It is not now desirable to apply separate names to the
different forms of the same mineral species, but these terms
answered the purpose, at the time, of making the subjects of study
more definite. A symbolical notation is the more convenient mode of
designating such forms, and such a notation Haüy invented; but the
symbols devised by him had many inconveniences, and have since been
superseded by the systems of other crystallographers.
Another of Haüy's leading merits was, as we have already intimated,
to have shown, more clearly than his predecessors had done, that the
crystalline angles of substances are a criterion of the substances;
and that this is peculiarly true of the _angles of cleavage_;--that
is, the angles of those edges which are obtained by cleaving a
crystal in two different directions;--a mode of division which the
structure of many kinds of crystals allowed him to execute in the
most complete manner. As an instance of the employment of this
criterion, I may mention his separation of the sulphates of baryta
and strontia, which had {323} previously been confounded. Among
crystals which in the collections were ranked together as "heavy
spar," and which were so perfect as to admit of accurate
measurement, he found that those which were brought from Sicily, and
those of Derbyshire, differed in their cleavage angle by three
degrees and a half. "I could not suppose," he says,[22\15] "that
this difference was the effect of any law of decrement; for it would
have been necessary to suppose so rapid and complex a law, that such
an hypothesis might have been justly regarded as an abuse of the
theory." He was, therefore, in great perplexity. But a little while
previous to this, Klaproth had discovered that there is an earth
which, though in many respects it resembles baryta, is different
from it in other respects; and this earth, from the place where it
was found (in Scotland), had been named _Strontia_. The French
chemists had ascertained that the two earths had, in some cases,
been mixed or confounded; and Vauquelin, on examining the Sicilian
crystals, found that their base was strontia, and not, as in the
Derbyshire ones, baryta. The riddle was now read; all the crystals
with the larger angle belong to the one, all those with the smaller,
to the other, of these two sulphates; and crystallometry was clearly
recognized as an authorized test of the difference of substances
which nearly resemble each other.
[Note 22\15: _Traité_, ii. 320.]
Enough has been said, probably, to enable the reader to judge how
much each of the two persons, now under review, contributed to
crystallography. It would be unwise to compare such contributions to
science with the great discoveries of astronomy and chemistry; and
we have seen how nearly the predecessors of Romé and Haüy had
reached the point of knowledge on which these two crystallographers
took their stand. But yet it is impossible not to allow, that in
these discoveries, which thus gave form and substance to the science
of crystallography, we have a manifestation of no common sagacity
and skill. Here, as in other discoveries, were required ideas and
facts;--clearness of geometrical conception which could deal with
most complex relations of form; a minute and extensive acquaintance
with actual crystals; and the talent and habit of referring these
facts to the general ideas. Haüy, in particular, was happily endowed
for his task. Without being a great mathematician, he was
sufficiently a geometer to solve all the problems which his
undertaking demanded; and though the mathematical reasoning might
have been made more compendious {324} by one who was more at home in
mathematical generalization, probably this could hardly have been
done without making the subject less accessible and less attractive
to persons moderately disciplined in mathematics. In all his
reasonings upon particular cases, Haüy is acute and clear; while his
general views appear to be suggested rather by a lively fancy than
by a sage inductive spirit: and though he thus misses the character
of a great philosopher, the vivacity of style, and felicity and
happiness of illustration, which grace his book, and which agree
well with the character of an Abbé of the old French monarchy, had a
great and useful influence on the progress of the subject.
Unfortunately Romé de Lisle and Haüy were not only rivals, but in
some measure enemies. The former might naturally feel some vexation
at finding himself, in his later years (he died in 1790), thrown
into shade by his more brilliant successor. In reference to Haüy's
use of cleavage, he speaks[23\15] of "innovators in crystallography,
who may properly be called _crystalloclasts_." Yet he adopted, in
great measure, the same views of the formation of crystals by
laminæ,[24\15] which Haüy illustrated by the destructive process at
which he thus sneers. His sensitiveness was kept alive by the
conduct of the Academy of Sciences, which took no notice of him and
his labors;[25\15] probably because it was led by Buffon, who
disliked Linnæus, and might dislike Romé as his follower; and who,
as we have seen, despised crystallography. Haüy revenged himself by
rarely mentioning Romé in his works, though it was manifest that his
obligations to him were immense; and by recording his errors while
he corrected them. More fortunate than his rival, Haüy was, from the
first, received with favor and applause. His lectures at Paris were
eagerly listened to by persons from all quarters of the world. His
views were, in this manner, speedily diffused; and the subject was
soon pursued, in various ways, by mathematicians and mineralogists
in every country of Europe.
[Note 23\15: Pref. p. xxvii.]
[Note 24\15: T. ii. p. 21.]
[Note 25\15: Marx. _Gesch. d. Cryst._ 130.]
CHAPTER III.
RECEPTION AND CORRECTIONS OF THE HAUÏAN CRYSTALLOGRAPHY.
I HAVE not hitherto noticed the imperfections of the
crystallographic views and methods of Haüy, because my business in
the last section {325} was to mark the permanent additions he made
to the science. His system did, however, require completion and
rectification in various points; and in speaking of the
crystallographers of the subsequent time, who may all be considered
as the cultivators of the Hauïan doctrines, we must also consider
what they did in correcting them.
The three main points in which this improvement was needed were;--a
better determination of the crystalline forms of the special
substances;--a more general and less arbitrary method of considering
crystalline forms according to their symmetry; and a detection of
more general conditions by which the crystalline angle is regulated.
The first of these processes may be considered as the natural sequel
of the Hauïan epoch: the other two must be treated as separate steps
of discovery.
When it appeared that the angle of natural or of cleavage faces
could be used to determine the differences of minerals, it became
important to measure this angle with accuracy. Haüy's measurements
were found very inaccurate by many succeeding crystallographers:
Mohs says[26\15] that they are so generally inaccurate, that no
confidence can be placed in them. This was said, of course,
according to the more rigorous notions of accuracy to which the
establishment of Haüy's system led. Among the persons who
principally labored in ascertaining, with precision, the crystalline
angles of minerals, were several Englishmen, especially Wollaston,
Phillips, and Brooke. Wollaston, by the invention of his Reflecting
Goniometer, placed an entirely new degree of accuracy within the
reach of the crystallographer; the angle of two faces being, in this
instrument, measured by means of the reflected images of bright
objects seen in them, so that the measure is the more accurate the
more minute the faces are. In the use of this instrument, no one was
more laborious and successful than William Phillips, whose power of
apprehending the most complex forms with steadiness and clearness,
led Wollaston to say that he had "a geometrical sense." Phillips
published a Treatise on Mineralogy, containing a great collection of
such determinations; and Mr. Brooke, a crystallographer of the same
exact and careful school, has also published several works of the
same kind. The precise measurement of crystalline angles must be the
familiar employment of all who study crystallography; and,
therefore, any further enumeration of those {326} who have added in
this way to the stock of knowledge, would be superfluous.
[Note 26\15: Marx. p. 153.]
Nor need I dwell long on those who added to the knowledge which Haüy
left, of derived forms. The most remarkable work of this kind was
that of Count Bournon, who published a work on a single mineral
(calcspar) in three quarto volumes.[27\15] He has here given
representations of seven hundred forms of crystals, of which,
however, only fifty-six are essentially different. From this example
the reader may judge what a length of time, and what a number of
observers and calculators, were requisite to exhaust the subject.
[Note 27\15: _Traité complet de la Chaux Carbonatée et d'Aragonite_,
par M. le Comte de Bournon. London, 1808.]
If the calculations, thus occasioned, had been conducted upon the
basis of Haüy's system, without any further generalization, they
would have belonged to that process, the natural sequel of inductive
discoveries, which we call _deduction_; and would have needed only a
very brief notice here. But some additional steps were made in the
upward road to scientific truth, and of these we must now give an
account.
CHAPTER IV.
ESTABLISHMENT OF THE DISTINCTION OF SYSTEMS OF
CRYSTALLIZATION.--WEISS AND MOHS.
IN Haüy's views, as generally happens in new systems, however true,
there was involved something that was arbitrary, something that was
false or doubtful, something that was unnecessarily limited. The
principal points of this kind were;--his having made the laws of
crystalline derivation depend so much upon cleavage;--his having
assumed an atomic constitution of bodies as an essential part of his
system; and his having taken a set of primary forms, which, being
selected by no general view, were partly superfluous, and partly
defective.
How far evidence, such as has been referred to by various
philosophers, has proved, or can prove, that bodies are constituted
of indivisible atoms, will be more fully examined in the work which
treats of the Philosophy of this subject. There can be little doubt
that the {327} portion of Haüy's doctrine which most riveted popular
attention and applause, was his dissection of crystals, in a manner
which was supposed to lead actually to their ultimate material
elements. Yet it is clear, that since the solids given by cleavage
are, in many cases, such as cannot make up a solid space, the
primary conception of a necessary geometrical identity between the
results of division and the elements of composition, which is the
sole foundation of the supposition that crystallography points out
the actual elements, disappears on being scrutinized: and when Haüy,
pressed by this difficulty, as in the case of fluor-spar, put his
integrant octohedral molecules together, touching by the edges only,
his method became an empty geometrical diagram, with no physical
meaning.
The real fact, divested of the hypothesis which was contained in the
fiction of decrements, was, that when the relation of the derivative
to the primary faces is expressed by means of numerical indices,
these numbers are integers, and generally very small ones; and this
was the form which the law gradually assumed, as the method of
derivation was made more general and simple by Weiss and others.
"When, in 1809, I published my Dissertation," says Weiss,[28\15] "I
shared the common opinion as to the necessity of the assumption and
the reality of the existence of a primitive form, at least in a
sense not very different from the usual sense of the expression.
While I sought," he adds, referring to certain doctrines of general
philosophy which he and others entertained, "a _dynamical_ ground
for this, instead of the untenable atomistic view, I found that, out
of my primitive forms, there was gradually unfolded to my hands,
that which really governs them, and is not affected by their casual
fluctuations, the fundamental relations of those Dimensions
according to which a multiplicity of internal oppositions,
necessarily and mutually interdependent, are developed in the mass,
each having its own polarity; so that the crystalline character is
co-extensive with these polarities."
[Note 28\15: _Mem. Acad. Berl._ 1816, p. 307.]
The "Dimensions" of which Weiss here speaks, are the _Axes of
Symmetry_ of the crystal; that is, those lines in reference to
which, every face is accompanied by other faces, having like
positions and properties. Thus a rhomb, or more properly a
_rhombohedron_,[29\15] of {328} calcspar may be placed with one of
its obtuse corners uppermost, so that all the three faces which meet
there are equally inclined to the vertical line. In this position,
every derivative face, which is obtained by any modification of the
faces or edges of the rhombohedron, implies either three or six such
derivative faces; for no one of the three upper faces of the
rhombohedron has any character or property different from the other
two; and, therefore, there is no reason for the existence of a
derivative from one of these primitive faces, which does not equally
hold for the other primitive faces. Hence the derivative forms will,
in all cases, contain none but faces connected by this kind of
correspondence. The axis thus made vertical will be an Axis of
Symmetry, and the crystal will consist of three divisions, ranged
round this axis, and exactly resembling each other. According to
Weiss's nomenclature, such a crystal is "three-and-three-membered."
[Note 29\15: I use this name for the solid figure, since _rhomb_ has
always been used for a plane figure.]
But this is only one of the kinds of symmetry which crystalline
forms may exhibit. They may have _three axes_ of complete and
_equal_ symmetry at right angles to each other, as the cube and the
regular octohedron;--or, _two axes_ of equal symmetry, perpendicular
to each other and to a _third axis_, which is not affected with the
same symmetry with which they are; such a figure is a square
pyramid;--or they may have _three_ rectangular _axes_, all of
_unequal_ symmetry, the modifications referring to each axis
separately from the other two.
These are essential and necessary distinctions of crystalline form;
and the introduction of a classification of forms founded on such
relations, or, as they were called, _Systems of Crystallization_,
was a great improvement upon the divisions of the earlier
crystallographers, for those divisions were separated according to
certain arbitrarily-assumed primary forms. Thus Romé de Lisle's
fundamental forms were, the tetrahedron, the cube, the octohedron,
the rhombic prism, the rhombic octohedron, the dodecahedron with
triangular faces: Haüy's primary forms are the cube, the
rhombohedron, the oblique rhombic prism, the right rhombic prism,
the rhombic dodecahedron, the regular octohedron, tetrahedron, and
six-sided prism, and the bipyramidal dodecahedron. This division, as
I have already said, errs both by excess and defect, for some of
these primary forms might be made derivatives from others; and no
solid reason could be assigned why they were not. Thus the cube may
be derived from the tetrahedron, by truncating the edges; and the
rhombic dodecahedron again from the cube, by truncating its edges;
while the square pyramid could not be legitimately identified with
the derivative of any of these forms; for if we were to {329} derive
it from the rhombic prism, why should the acute angles always suffer
decrements corresponding in a certain way to those of the obtuse
angles, as they must do in order to give rise to a square pyramid?
The introduction of the method of reference to Systems of
Crystallization has been a subject of controversy, some ascribing
this valuable step to Weiss, and some to Mohs.[30\15] It appears, I
think, on the whole, that Weiss first published works in which the
method is employed; but that Mohs, by applying it to all the known
species of minerals, has had the merit of making it the basis of
real crystallography. Weiss, in 1809, published a Dissertation _On
the mode of investigating the principal geometrical character of
crystalline forms_, in which he says,[31\15] "No part, line, or
quantity, is so important as the axis; no consideration is more
essential or of a higher order than the relation of a crystalline
plane to the axis;" and again, "An axis is any line governing the
figure, about which all parts are similarly disposed, and with
reference to which they correspond mutually." This he soon followed
out by examination of some difficult cases, as Felspar and Epidote.
In the Memoirs of the Berlin Academy,[32\15] for 1814-15, he
published _An Exhibition of the natural Divisions of Systems of
Crystallization_. In this Memoir, his divisions are as follows:--The
_regular_ system, the _four-membered_, the _two-and-two-membered_,
the _three-and-three-membered_, and some others of inferior degrees
of symmetry. These divisions are by Mohs (_Outlines of Mineralogy_,
1822), termed the _tessular_, _pyramidal_, _prismatic_, and
_rhombohedral_ systems respectively. Hausmann, in his
_Investigations concerning the Forms of Inanimate Nature_,[33\15]
makes a nearly corresponding arrangement;--the _isometric_,
_monodimetric_, _trimetric_, and _monotrimetic_; and one or other of
these sets of terms have been adopted by most succeeding writers.
[Note 30\15: _Edin. Phil. Trans._ 1823, vols. xv. and xvi.]
[Note 31\15: pp. 16, 42.]
[Note 32\15: Ibid.]
[Note 33\15: Göttingen, 1821.]
In order to make the distinctions more apparent, I have purposely
omitted to speak of the systems which arise when the _prismatic_
system loses some part of its symmetry;--when it has only half or a
quarter its complete number of faces;--or, according to Mohs's
phraseology, when it is _hemihedral_ or _tetartohedral_. Such
systems are represented by the singly-oblique or doubly-oblique
prism; they are termed by Weiss _two-and-one-membered_, and
_one-and-one-membered_; by other writers, _Monoklinometric_, and
_Triklinometric_ Systems. There are also other {330} peculiarities
of Symmetry, such, for instance, as that of the _plagihedral_ faces
of quartz, and other minerals.
The introduction of an arrangement of crystalline forms into
systems, according to their degree of symmetry, was a step which was
rather founded on a distinct and comprehensive perception of
mathematical relations, than on an acquaintance with experimental
facts, beyond what earlier mineralogists had possessed. This
arrangement was, however, remarkably confirmed by some of the
properties of minerals which attracted notice about the time now
spoken of, as we shall see in the next chapter.
CHAPTER V.
RECEPTION AND CONFIRMATION OF THE DISTINCTION OF SYSTEMS OF
CRYSTALLIZATION.
DIFFUSION OF THE DISTINCTION OF SYSTEMS.--The distinction of systems
of crystallization was so far founded on obviously true views, that
it was speedily adopted by most mineralogists. I need not dwell on
the steps by which this took place. Mr. Haidinger's translation of
Mohs was a principal occasion of its introduction in England. As an
indication of dates, bearing on this subject, perhaps I may be
allowed to notice, that there appeared in the _Philosophical
Transactions for_ 1825, _A General Method of Calculating the
**Angles of Crystals_, which I had written, and in which I referred
only to Haüy's views; but that in 1826,[34\15] I published a Memoir
_On the Classification of Crystalline Combinations_, founded on the
methods of Weiss and Mohs, especially the latter; with which I had
in the mean time become acquainted, and which appeared to me to
contain their own evidence and recommendation. General methods, such
as was attempted in the Memoir just quoted, are part of that process
in the history of sciences, by which, when the principles are once
established, the mathematical operation of deducing their
consequences is made more and more general and symmetrical: which we
have seen already exemplified in the history of celestial mechanics
after the time of Newton. It does not enter into our plan, to dwell
upon the various steps in this way {331} made by Levy, Naumann,
Grassmann, Kupffer, Hessel, and by Professor Miller among ourselves.
I may notice that one great improvement was, the method introduced
by Monteiro and Levy, of determining the laws of derivation of
forces by means of the _parallelisms of edges_; which was afterwards
extended so that faces were considered as belonging to _zones_. Nor
need I attempt to enumerate (what indeed it would be difficult to
describe in words) the various methods of _notation_ by which it has
been proposed to represent the faces of crystals, and to facilitate
the calculations which have reference to them.
[Note 34\15: _Camb. Trans._ vol. ii. p. 391.]
[2nd Ed.] [My Memoir of 1825 depended on the views of Haüy in so far
as that I started from his "primitive forms;" but being a general
method of expressing all forms by co-ordinates, it was very little
governed by these views. The mode of representing crystalline forms
which I proposed seemed to contain its own evidence of being more
true to nature than Haüy's theory of decrements, inasmuch as my
method expressed the faces at much lower numbers. I determine a face
by means of the dimensions of the primary form _divided_ by certain
numbers; Haüy had expressed the face virtually by the same
dimensions _multiplied_ by numbers. In cases where my notation gives
such numbers as (3, 4, 1), (1, 3, 7), (5, 1, 19), his method
involves the higher numbers (4, 3, 12), (21, 7, 3), (19, 95, 5). My
method however has, I believe, little value as a method of
"_calculating_ the angles of crystals."
M. Neumann, of Königsberg, introduced a very convenient and elegant
mode of representing the position of faces of crystals by
corresponding points on the surface of a circumscribing sphere. He
gave (in 1823) the laws of the derivation of crystalline faces,
expressed geometrically by the intersection of zones, (_Beiträge zur
Krystallonomie_.) The same method of indicating the position of
faces of crystals was afterwards, together with the notation,
re-invented by M. Grassmann, (_Zur Krystallonomie und Geometrischen
Combinationslehre_, 1829.) Aiding himself by the suggestions of
these writers, and partly adopting my method, Prof. Miller has
produced a work on Crystallography remarkable for mathematical
elegance and symmetry; and has given expressions really useful for
calculating the angles of crystalline faces, (_A Treatise on
Crystallography_. Cambridge, 1839.)]
_Confirmation of the Distinction of Systems by the Optical
Properties of Minerals.--Brewster._--I must not omit to notice the
striking confirmation which the distinction of systems of
crystallization received from optical discoveries, especially those
of Sir D. Brewster. Of the {332} history of this very rich and
beautiful department of science, we have already given some account,
in speaking of Optics. The first facts which were noticed, those
relating to double refraction, belonged exclusively to crystals of
the rhombohedral system. The splendid phenomena of the rings and
lemniscates produced by dipolarizing crystals, were afterwards
discovered; and these were, in 1817, classified by Sir David
Brewster, according to the crystalline forms to which they belong.
This classification, on comparison with the distinction of Systems
of Crystallization, resolved itself into a necessary relation of
mathematical symmetry: all crystals of the pyramidal and
rhombohedral systems, which from their geometrical character have a
single axis of symmetry, are also optically uniaxal, and produce by
dipolarization circular rings; while the prismatic system, which has
no such single axis, but three unequal axes of symmetry, is optically
biaxal, gives lemniscates by dipolarized light, and according to
Fresnel's theory, has three rectangular axes of unequal elasticity.
[2nd Ed.] [I have placed Sir David Brewster's arrangement of
crystalline forms in this chapter, as an event belonging to the
_confirmation_ of the distinctions of forms introduced by Weiss and
Mohs; because that arrangement was established, not on
crystallographical, but on optical grounds. But Sir David Brewster's
optical discovery was a much greater step in science than the
systems of the two German crystallographers; and even in respect to
the crystallographical principle, Sir D. Brewster had an independent
share in the discovery. He divided crystalline forms into three
classes, enumerating the Hauïan "primitive forms" which belonged to
each; and as he found some exceptions to this classification, (such
as idocrase, &c.,) he ventured to pronounce that in those substances
the received primitive forms were probably erroneous; a judgment
which was soon confirmed by a closer crystallographical scrutiny. He
also showed his perception of the mineralogical importance of his
discovery by publishing it, not only in the _Phil. Trans._ (1818),
but also in the _Transactions of the Wernerian Society of Natural
History_. In a second paper inserted in this later series, read in
1820, he further notices Mohs's System of Crystallography, which had
then recently appeared, and points out its agreement with his own.
Another reason why I do not make his great optical discovery a
cardinal point in the history of crystallography is, that as a
crystallographical system it is incomplete. Although we are thus led
to distinguish the _tessular_ and the _prismatic_ systems (using
Mohs's terms) {333} from the _rhombohedral_ and the _square
prismatic_, we are not led to distinguish the latter two from each
other; inasmuch as they have no optical difference of character. But
this distinction is quite essential in crystallography; for these
two systems have faces formed by laws as different as those of the
other two systems.
Moreover, Weiss and Mohs not only divided crystalline forms into
certain classes, but showed that by doing this, the derivation of
all the existing forms from the fundamental ones assumed a new
aspect of simplicity and generality; and this was the essential part
of what they did.
On the other hand, I do not think it is too much to say as I have
elsewhere said[35\15] that "Sir D. Brewster's optical experiments
must have led to a classification of crystals into the above
systems, or something nearly equivalent, even if crystals had not
been so arranged by attention to their forms."]
[Note 35\15: _Philosophy of the Inductive Sciences_, B. viii. C.
iii. Art. 3.]
Many other most curious trains of research have confirmed the
general truth, that the degree and kind of geometrical symmetry
corresponds exactly with the symmetry of the optical properties. As
an instance of this, eminently striking for its singularity, we may
notice the discovery of Sir John Herschel, that the _plagihedral_
crystallization of quartz, by which it exhibits faces _twisted_ to
the right or the left, is accompanied by right-handed or left-handed
circular polarization respectively. No one acquainted with the
subject can now doubt, that the correspondence of geometrical and
optical symmetry is of the most complete and fundamental kind.
[2nd Ed.] [Our knowledge with respect to the positions of the
optical axes of the oblique prismatic crystals is still imperfect.
It appears to be ascertained that, in singly oblique crystals, one
of the axes of optical elasticity coincides with the rectangular
crystallographic axis. In doubly oblique crystals, one of the axes
of optical elasticity is, in many cases, coincident with the axis of
a principal zone. I believe no more determinate laws have been
discovered.]
Thus the highest generalization at which mathematical
crystallographers have yet arrived, may be considered as fully
established; and the science of Crystallography, in the condition in
which these place it, is fit to be employed as one of the members of
Mineralogy, and thus to fill its appropriate place and office. {334}
CHAPTER VI.
CORRECTION OF THE LAW OF THE SAME ANGLE FOR THE SAME SUBSTANCE.
DISCOVERY OF ISOMORPHISM. MITSCHERLICH.--The discovery of which we
now have to speak may appear at first sight too large to be included
in the history of crystallography, and may seem to belong rather to
chemistry. But it is to be recollected that crystallography, from
the time of its first assuming importance in the hands of Haüy,
founded its claim to notice entirely upon its connexion with
chemistry; crystalline forms were properties of _something_; but
_what_ that something was, and how it might be modified without
becoming something else, no crystallographer could venture to
decide, without the aid of chemical analysis. Haüy had assumed, as
the general result of his researches, that the same chemical
elements, combined in the same proportions, would always exhibit the
same crystalline form; and reciprocally, that the same form and
angles (except in the obvious case of the tessular system, in which
the angles are determined by its _being_ the tessular system,)
implied the same chemical constitution. But this dogma could only be
considered as an approximate conjecture; for there were many glaring
and unexplained exceptions to it. The explanation of several of
these was beautifully described by the discovery that there are
various elements which are _isomorphous_ to each other; that is,
such that one may take the place of another without altering the
crystalline form; and thus the chemical composition may be much
changed, while the crystallographic character is undisturbed.
This truth had been caught sight of, probably as a guess only, by
Fuchs as early as 1815. In speaking of a mineral which had been
called Gehlenite, he says, "I hold the oxide of iron, not for an
essential component part of this genus, but only as a _vicarious_
element, replacing so much lime. We shall find it necessary to
consider the results of several analyses of mineral bodies in this
point of view, if we wish, on the one hand, to bring them into
agreement with the doctrine of chemical proportions, and on the
other, to avoid unnecessarily splitting up genera." In a lecture _On
the Mutual Influence of_ {335} _Chemistry and Mineralogy_,[36\15] he
again draws attention to his term _vicarious_ (_vicarirende_), which
undoubtedly expresses the nature of the general law afterwards
established by Mitscherlich in 1822.
[Note 36\15: Munich, 1820.]
But Fuchs's conjectural expression was only a prelude to
Mitscherlich's experimental discovery of isomorphism. Till many
careful analyses had given substance and signification to this
conception of vicarious elements, it was of small value. Perhaps no
one was more capable than Berzelius of turning to the best advantage
any ideas which were current in the chemical world; yet we find
him,[37\15] in 1820, dwelling upon a certain vague view of these
cases,--that "oxides which contain equal doses of oxygen must have
their general properties common;" without tracing it to any definite
conclusions. But his scholar, Mitscherlich, gave this proposition a
real crystallographical import. Thus he found that the carbonates of
lime (calcspar,) of magnesia, of protoxide of iron, and of protoxide
of manganese, agree in many respects of form, while the homologous
angles vary through one or two degrees only; so again the carbonates
of baryta, strontia, lead, and lime (arragonite), agree nearly; the
different kinds of felspar vary only by the substitution of one
alkali for another; the phosphates are almost identical with the
arseniates of several bases. These, and similar results, were
expressed by saying that, in such cases, the bases, lime, protoxide
of iron, and the rest, are _isomorphous_; or in the latter instance,
that the arsenic and phosphoric acids are isomorphous.
[Note 37\15: _Essay on the Theory of Chemical Proportions_, p. 122.]
Since, in some of these cases, the substitution of one element of
the isomorphous group for another does alter the angle, though
slightly, it has since been proposed to call such groups
_plesiomorphous_.
This discovery of isomorphism was of great importance, and excited
much attention among the chemists of Europe. The history of its
reception, however, belongs, in part, to the classification of
minerals; for its effect was immediately to metamorphose the
existing chemical systems of arrangement. But even those
crystallographers and chemists who cared little for general systems
of classification, received a powerful impulse by the expectation,
which was now excited, of discovering definite laws connecting
chemical constitution with crystalline form. Such investigations
were soon carried on with great activity. Thus, at a recent period,
Abich analysed a number of tessular minerals, spinelle, pleonaste,
gahnite, franklinite, and chromic iron oxide; and {336} seems to
have had some success in **giving a common type to their chemical
formulæ, as there is a common type in their crystallization.
[2nd Ed.] [It will be seen by the above account that Prof.
Mitscherlich's merit in the great discovery of Isomorphism is not at
all narrowed by the previous conjectures of M. Fuchs. I am informed,
moreover, that M. Fuchs afterwards (in Schweigger's _Journal_)
retracted the opinions he had put forward on this subject.]
_Dimorphism._--My business is, to point out the connected truths
which have been obtained by philosophers, rather than insulated
difficulties which still stand out to perplex them. I need not,
therefore, dwell on the curious cases of _dimorphism_; cases in
which the same definite chemical compound of the same elements
appears to have two different forms; thus the carbonate of lime has
two forms, _calcspar_ and _arragonite_, which belong to different
systems of crystallization. Such facts may puzzle us; but they
hardly interfere with any received general truths, because we have
as yet no truths of very high order respecting the connexion of
chemical constitution and crystalline form. Dimorphism does not
interfere with isomorphism; the two classes of facts stand at the
same stage of inductive generalization, and we wait for some higher
truth which shall include both, and rise above them.
[2nd Ed.] [For additions to our knowledge of the Dimorphism of
Bodies, see Professor Johnstone's valuable _Report_ on that subject
in the _Reports of the British Association_ for 1837. Substances
have also been found which are _trimorphous_. We owe to Professor
Mitscherlich the discovery of dimorphism, as well as of isomorphism:
and to him also we owe the greater part of the knowledge to which
these discoveries have led.]
CHAPTER VII.
ATTEMPTS TO ESTABLISH THE FIXITY OF OTHER PHYSICAL
PROPERTIES.--WERNER.
THE reflections from which it appeared, (at the end of the last
Book,) that in order to obtain general knowledge respecting bodies,
we must give scientific fixity to our appreciation of their
properties, applies to their other properties as well as to their
crystalline {337} form. And though none of the other properties have
yet been referred to standards so definite as that which geometry
supplies for crystals, a system has been introduced which makes
their measures far more constant and precise than they are to a
common undisciplined sense.
The author of this system was Abraham Gottlob Werner, who had been
educated in the institutions which the Elector of Saxony had
established at the mines of Freiberg. Of an exact and methodical
intellect, and of great acuteness of the senses, Werner was well
fitted for the task of giving fixity to the appreciation of outward
impressions; and this he attempted in his _Dissertation on the
external Characters of Fossils_, which was published at Leipzig in
1774. Of the precision of his estimation of such characters, we may
judge from the following story, told by his biographer
Frisch.[38\15] One of his companions had received a quantity of
pieces of amber, and was relating to Werner, then very young, that
he had found in the lot one piece from which he could extract no
signs of electricity. Werner requested to be allowed to put his hand
in the bag which contained these pieces, and immediately drew out
the unelectrical piece. It was yellow chalcedony, which is
distinguishable from amber by its weight and coldness.
[Note 38\15: _Werner's Leben_, p. 26.]
The principal external characters which were subjected by Werner to
a systematic examination were color, lustre, hardness, and specific
gravity. His subdivisions of the first character (_Color_), were
very numerous; yet it cannot be doubted that if we recollect them by
the eye, and not by their names, they are definite and valuable
characters, and especially the metallic colors. Breithaupt, merely
by the aid of this character, distinguished two new compounds among
the small grains found along with the grains of platinum, and
usually confounded with them. The kinds of _Lustre_, namely,
_glassy_, _fatty_, _adamantine_, _metallic_, are, when used in the
same manner, equally valuable. _Specific Gravity_ obviously admits
of a numerical measure; and the _Hardness_ of a mineral was pretty
exactly defined by the substances which it would scratch, and by
which it was capable of being scratched.
Werner soon acquired a reputation as a mineralogist, which drew
persons from every part of Europe to Freiberg in order to hear his
lectures; and thus diffused very widely his mode of employing
external characters. It was, indeed, impossible to attend so closely
to {338} these characters as the Wernerian method required, without
finding that they were more distinctive than might at first sight be
imagined; and the analogy which this mode of studying Mineralogy
established between that and other branches of Natural History,
recommended the method to those in whom a general inclination to
such studies was excited. Thus Professor Jameson of Edinburgh, who
had been one of the pupils of Werner at Freiberg, not only published
works in which he promulgated the mineralogical doctrines of his
master, but established in Edinburgh a "Wernerian Society," having
for its object the general cultivation of Natural History.
Werner's standards and nomenclature of external characters were
somewhat modified by Mohs, who, with the same kinds of talents and
views, succeeded him at Freiberg. Mohs reduced hardness to numerical
measure by selecting ten known minerals, each harder than the other
in order, from _talc_ to _corundum_ and _diamond_, and by making the
place which these minerals occupy in the list, the numerical measure
of the hardness of those which are compared with them. The result of
the application of this fixed measurement and nomenclature of
external characters will appear in the History of Classification, to
which we now proceed.
{{339}}
SYSTEMATIC MINERALOGY.
CHAPTER VIII.
ATTEMPTS AT THE CLASSIFICATION OF MINERALS.
_Sect._ 1.--_Proper object of Classification._
THE fixity of the crystalline and other physical properties of
minerals is turned to account by being made the means of classifying
such objects. To use the language of Aristotle,[39\15]
Classification is the _architectonic_ science, to which
Crystallography and the Doctrine of External Characters are
subordinate and ministerial, as the art of the bricklayer and
carpenter are to that of the architect. But classification itself is
useful only as subservient to an ulterior science, which shall
furnish us with knowledge concerning things so classified. To
classify is to divide and to name; and the value of the Divisions
which we thus make, and of the names which we give them, is
this;--that they render exact knowledge and general propositions
possible. Now the knowledge which we principally seek concerning
minerals is a knowledge of their chemical composition; the general
propositions to which we hope to be led are such as assert relations
between their intimate constitution and their external attributes.
Thus our Mineralogical Classification must always have an eye turned
towards Chemistry. We cannot get rid of the fundamental conviction,
that the elementary composition of bodies, since it fixes their
essence, must determine their properties. Hence all mineralogical
arrangements, whether they profess it or not, must be, in effect,
chemical; they must have it for their object to bring into view a
set of relations, which, whatever else they may be, are at least
chemical relations. We may begin with the outside, but it is only in
order to reach the inner {340} structure. We may classify without
reference to chemistry; but if we do so, it is only that we may
assert chemical propositions with reference to our classification.
[Note 39\15: _Eth. Nicom._ i. 2.]
But, as we have already attempted to show, we not only may, but we
_must_ classify, by other than chemical characters, in order to be
able to make our classification the basis of chemical knowledge. In
order to assert chemical truths concerning bodies, we must have the
bodies known by some tests not chemical. The chemist cannot assert
that Arragonite does or does not contain Strontia, except the
mineralogist can tell him whether any given specimen is or is not
_Arragonite_. If chemistry be called upon to supply the
_definitions_ as well as the _doctrines_ of mineralogy, the science
can only consist of identical propositions.
Yet chemistry has been much employed in mineralogical
classifications, and, it is generally believed, with advantage to
the science: How is this consistent with what has been said?
To this the answer is, that when this _has_ been done with
advantage, the authority of external characters, as well as of
chemical constitution, has really been brought into play. We have
two sets of properties to compare, chemical and physical; to exhibit
the connexion of these is the object of scientific mineralogy. And
though this connexion would be most distinctly asserted, if we could
keep the two sets of properties distinct, yet it may be brought into
view in a great degree, by classifications in which both are
referred to as guides. Since the governing principle of the attempts
at classification is the conviction that the chemical constitution
and the physical properties have a definite relation to each other,
we appear entitled to use both kinds of evidence, in proportion as
we can best obtain each; and then the general consistency and
convenience of our system will be the security for its containing
substantial knowledge, though this be not presented in a rigorously
logical or systematic form.
Such _mixed systems_ of classification, resting partly on chemical
and partly on physical characters, naturally appeared as the
earliest attempts in this way, before the two members of the subject
had been clearly separated in men's minds; and these systems,
therefore, we must first give an account of.
_Sect._ 2.--_Mixed Systems of Classification._
_Early Systems._--The first attempts at classifying minerals went
upon the ground of those differences of general aspect which had
been {341} recognized in the formation of common language; as
_earths_, _stones_, _metals_. But such arrangements were manifestly
vague and confused; and when chemistry had advanced to power and
honor, her aid was naturally called in to introduce a better order.
"Hiarne and Bromell were, as far as I know," says[40\15] Cronstedt,
"the first who founded any mineral system upon chemical principles;
to them we owe the three known divisions of the most simple mineral
bodies; viz., the _calcarei_, _vitrescentes_, and _apyri_." But
Cronstedt's own _Essay towards a System of Mineralogy_, published in
Swedish in 1758, had perhaps more influence than any other, upon
succeeding systems. In this, the distinction of earths and stones,
and also of vitrescent and non-vitrescent earths (_apyri_), is
rejected. The earths are classed as _calcareous_, _siliceous_,
_argillaceous_, and the like. Again, calcareous earth is pure (_calc
spar_), or united with acid of vitriol (_gypsum_), or united with
the muriatic add (_sal ammoniac_), and the like. It is easy to see
that this is the method, which, in its general principle, has been
continued to our own time. In such methods, it is supposed that we
can recognize the substance by its general appearance, and on this
assumption, its place in the system conveys to us chemical knowledge
concerning it.
[Note 40\15: _Mineralogy_, Pref. p. viii.]
But as the other branches of Natural History, and especially Botany,
assumed a systematic form, many mineralogists became dissatisfied
with this casual and superficial mode of taking account of external
characters; they became convinced, that in Mineralogy as in other
sciences, classification must have its system and its rules. The
views which Werner ascribes to his teacher, Pabst van Ohain,[41\15]
show the rise of those opinions which led through Werner to Mohs:
"He was of opinion that a natural mineral system must be constructed
by chemical determinations, and external characters at the same time
(_methodus mixta_); but that along with this, mineralogists ought
also to construct and employ what he called an _artificial system_,
which might serve us as a guide (_loco indicis_) how to introduce
newly-discovered fossils into the system, and how to find easily and
quickly those already known and introduced." Such an artificial
system, containing not the grounds of classification, but marks for
recognition, was afterwards attempted by Mohs, and termed by him the
_Characteristic_ of his system.
[Note 41\15: Frisch. _Werner's Leben_, p. 15.]
_Werner's System._--But, in the mean time, Werner's classification
had an extensive reign, and this was still a mixed system. Werner
himself, indeed, never published a system of mineralogy. "We might
{342} almost imagine," Cuvier says,[42\15] "that when he had
produced his nomenclature of external characters, he was affrighted
with his own creation; and that the reason of his writing so little
after his first essay, was to avoid the shackles which he had
imposed upon others." His system was, indeed, made known both in and
out of Germany, by his pupils; but in consequence of Werner's
unwillingness to give it on his own authority, it assumed, in its
published forms, the appearance of an extorted secret imperfectly
told. A _Notice of the Mineralogical Cabinet of Mine-Director Pabst
von Ohain_, was, in 1792, published by Karsten and Hoffman, under
Werner's direction; and conveyed by example, his views of
mineralogical arrangement; and[43\15] in 1816 his _Doctrine of
Classification_ was surreptitiously copied from his manuscript, and
published in a German Journal, termed _The Hesperus_. But it was
only in 1817, after his death, that there appeared _Werner's Last
Mineral System_, edited from his papers by Breithaupt and Köhler:
and by this time, as we shall soon see, other systems were coming
forwards on the stage.
[Note 42\15: Cuv. _El._ ii. 314.]
[Note 43\15: Frisch. p. 52.]
A very slight notice of Werner's arrangement will suffice to show
that it was, as we have termed it, a Mixed System. He makes four
great Classes of fossils, _Earthy_, _Saline_, _Combustible_,
_Metallic_: the earthy fossils are in eight Genera--Diamond, Zircon,
Silica, Alumina, Talc, Lime, Baryta, Hallites. It is clear that
these genera are in the main chemical, for chemistry alone can
definitely distinguish the different Earths which characterize them.
Yet the Wernerian arrangement supposed the distinctions to be
practically made by reference to those external characters which the
teacher himself could employ with such surpassing skill. And though
it cannot be doubted, that the chemical views which prevailed around
him had a latent influence on his classification in some cases, he
resolutely refused to bend his system to the authority of chemistry.
Thus,[44\15] when he was blamed for having, in opposition to the
chemists, placed diamond among the earthy fossils, he persisted in
declaring that, mineralogically considered, it was a stone, and
could not be treated as anything else.
[Note 44\15: Frisch. p. 62.]
This was an indication to that tendency, which, under his successor,
led to a complete separation of the two grounds of classification.
But before we proceed to this, we must notice what was doing at this
period in other parts of Europe.
_Haüy's System._--Though Werner, on his own principles, ought to
{343} have been the first person to see the immense value of the
most marked of external characters, crystalline form, he did not, in
fact, attach much importance to it. Perhaps he was in some measure
fascinated by a fondness for those characters which he had himself
systematized, and the study of which did not direct him to look for
geometrical relations. However this may be, the glory of giving to
Crystallography its just importance in Mineralogy is due to France:
and the Treatise of Haüy, published in 1801, is the basis of the
best succeeding works of mineralogy. In this work, the arrangement
is professedly chemical; and the classification thus established is
employed as the means of enunciating crystallographic and other
properties. "The principal object of this Treatise," says the
author,[45\15] "is the exposition and development of a method
founded on certain principles, which may serve as a frame-work for
all the knowledge which Mineralogy can supply, aided by the
different sciences which can join hands with her and march on the
same line.**" It is worthy of notice, as characteristic of this
period of Mixed Systems, that the classification of Haüy, though
founded on principles so different from the Wernerian ones, deviates
little from it in the general character of the divisions. Thus, the
first Order of the first Class of Haüy is _Acidiferous Earthy
Substances_; the first genus is _Lime_; the species are, _Carbonate
of Lime_, _Phosphate of Lime_, _Fluate of Lime_, _Sulphate of Lime_,
and so on.
[Note 45\15: Disc. Prél. p. xvii.]
_Other Systems._--Such mixed methods were introduced also into this
country, and have prevailed, we may say, up to the present time. The
_Mineralogy_ of William Phillips, which was published in 1824, and
which was an extraordinary treasure of crystallographic facts, was
arranged by such a mixed system; that is, by a system professedly
chemical; but, inasmuch as a rigid chemical system is impossible,
and the assumption of such a one leads into glaring absurdities, the
system was, in this and other attempts of the same kind, corrected
by the most arbitrary and lax application of other considerations.
It is a curious example of the difference of national intellectual
character, that the manifest inconsistencies of the prevalent
systems, which led in Germany, as we shall see, to bold and sweeping
attempts at reform, produced in England a sort of contemptuous
despair with regard to systems in general;--a belief that no system
could be consistent or useful;--and a persuasion that the only
valuable knowledge is the accumulation of particular facts. This is
not the place to {344} explain how erroneous and unphilosophical
such an opinion is. But we may notice that while such a temper
prevails among us, our place in this science can never be found in
advance of that position which we are now considering as exemplified
in the period of Werner and Haüy. So long as we entertain such views
respecting the objects of Mineralogy, we can have no share in the
fortunes of the succeeding period of its history, to which I now
proceed.
CHAPTER IX.
ATTEMPTS AT THE REFORM OF MINERALOGICAL SYSTEMS.--SEPARATION OF THE
CHEMICAL AND NATURAL HISTORY METHODS.
_Sect._ 1.--_Natural History System of Mohs._
THE chemical principle of classification, if pursued at random, as
in the cases just spoken of leads to results at which a
philosophical spirit revolts; it separates widely substances which
are not distinguishable; joins together bodies the most dissimilar;
and in hardly any instance does it bring any truth into view. The
vices of classifications like that of Haüy could not long be
concealed; but even before time had exposed the weakness of his
system, Haüy himself had pointed out, clearly and without
reserve,[46\15] that a chemical system is only one side of the
subject, and supposes, as its counterpart, a science of external
characters. In the mean time, the Wernerians were becoming more and
more in love with the form which they had given to such a science.
Indeed, the expertness which Werner and his scholars acquired in the
use of external characters, justified some partiality for them. It
is related of him,[47\15] that, by looking at a piece of iron-ore,
and poising it in his hand, he was able to tell, almost precisely,
the proportion of pure metal which it contained. And in the last
year of his life,[48\15] he had marked out, as the employment of the
ensuing winter, the study of the system of Berzelius, with a view to
find out the laws of combination as disclosed by external
characters. In the same spirit, his pupil {345} Breithaupt[49\15]
attempted to discover the ingredients of minerals by their
peculiarities of crystallization. The persuasion that there must be
_some_ connexion between composition and properties, transformed
itself, in their minds, into a belief that they could seize the
nature of the connexion by a sort of instinct.
[Note 46\15: See his Disc. Prél.]
[Note 47\15: Frisch. _Werner's Leben_, p. 78.]
[Note 48\15: Frisch. 3.]
[Note 49\15: _Dresdn. Auswahl_, vol. ii. p. 97.]
This opinion of the independency of the science of external
characters, and of its sufficiency for its own object, at last
assumed its complete form in the bold attempt to construct a system
which should borrow nothing from chemistry. This attempt was made by
Frederick Mohs, who had been the pupil of Werner, and was afterwards
his successor in the school of Freiberg; and who, by the acute and
methodical character of his intellect, and by his intimate knowledge
of minerals, was worthy of his predecessor. Rejecting altogether all
divisions of which the import was chemical, Mohs turned for
guidance, or at least for the light of analogy, to botany. His
object was to construct a _Natural System_ of mineralogy. What the
conditions and advantages of a natural system of any province of
nature are, we must delay to explain till we have before us, in
botany, a more luminous example of such a scheme. But further; in
mineralogy, as in botany, besides the Natural System, by which we
_form_ our classes, it is necessary to have an _Artificial System_
by which we _recognize_ them;--a principle which, we have seen, had
already taken root in the school of Freiberg. Such an artificial
system Mohs produced in his _Characteristic of the Mineral Kingdom_,
which was published at Dresden in 1820; and which, though extending
only to a few pages, excited a strong interest in Germany, where
men's minds were prepared to interpret the full import of such a
work. Some of the traits of such a "Characteristic" had, indeed,
been previously drawn by others; as for example, by Haüy, who
notices that each of his Classes has peculiar characters. For
instance, his First Class (acidiferous substances,) alone possesses
these combinations of properties; "division into a regular
octohedron, without being able to scratch glass; specific gravity
above 3·5, without being able to scratch glass." The extension of
such characters into a scheme which should exhaust the whole mineral
kingdom, was the undertaking of Mohs.
Such a collection of marks of classes, implied a classification
previously established, and accordingly, Mohs had created his own
mineral system. His aim was to construct it, as we shall hereafter
see that other natural systems are constructed, by taking into
account _all_ the {346} resemblances and differences of the objects
classified. It is obvious that to execute such a work, implied a
most intimate and universal acquaintance with minerals;--a power of
combining in one vivid survey the whole mineral kingdom. To
illustrate the spirit in which Professor Mohs performed his task, I
hope I may be allowed to refer to my own intercourse with him. At an
early period of my mineralogical studies, when the very conception
of a Natural System was new to me, he, with great kindliness of
temper, allowed me habitually to propose to him the scruples which
arose in my mind, before I could admit principles which appeared to
me then so vague and indefinite; and answered my objections with
great patience and most instructive clearness. Among other
difficulties, I one day propounded to him this;--"You have published
a Treatise on Mineralogy, in which you have described _all_ the
important properties of all known minerals. On your principles,
then, it ought to be possible, merely by knowing the descriptions in
your book, and without seeing any minerals, to construct a natural
system; and this natural system ought to turn out identical with
that which you have produced, by so careful an examination of the
minerals themselves." He pondered a moment, and then he answered,
"It is true; but what an enormous _imagination_ (_einbildungskraft_,
_power of inward imagining_), a man must have for such a work!"
Vividness of conception of sensible properties, and the steady
intuition (_anschauung_) of objects, were deemed by him, and by the
Wernerian school in general, to be the most essential conditions of
complete knowledge.
It is not necessary to describe Mohs's system in detail; it may
sufficiently indicate its form to state that the following
substances, such as I before gave as examples of other arrangements,
calcspar, gypsum, fluor spar, apatite, heavy spar, are by Mohs
termed respectively, _Rhombohedral Lime Haloide_, _Gyps Haloide_,
_Octohedral Fluor Haloide_, _Rhombohedral Fluor Haloide_, _Prismatic
Hal Baryte_. These substances are thus referred to the _Orders_
Haloide, and Baryte; to _Genera_ Lime Haloide, Fluor Haloide, Hal
Baryte; and the _Species_ is an additional particularization.
Mohs not only aimed at framing such a system, but was also ambitious
of giving to all minerals _Names_ which should accord with the
system. This design was too bold to succeed. It is true, that a new
nomenclature was much needed in mineralogy: it is true, too, that it
was reasonable to expect, from an improved classification, an
improved nomenclature, such as had been so happily obtained in
botany by the {347} reform of Linnæus. But besides the defects of
Mohs's system, he had not prepared his verbal novelties with the
temperance and skill of the great botanical reformer. He called upon
mineralogists to change the name of almost every mineral with which
they were acquainted; and the proposed appellations were mostly of a
cumbrous form, as the above example may serve to show. Such names
could have obtained general currency, only after a general and
complete acceptance of the system; and the system did not possess,
in a sufficient degree, that evidence which alone could gain it a
home in the belief of philosophers,--the coincidence of its results
with those of Chemistry. But before I speak finally of the fortunes
of the Natural-history System, I will say something of the other
attempt which was made about the same time to introduce a Reform
into Mineralogy from the opposite extremity of the science.
_Sect._ 2.--_Chemical System of Berzelius and others._
IF the students of external characters were satisfied of the
independence of their method, the chemical analysts were naturally
no less confident of the legitimate supremacy of their principles:
and when the beginning of the present century had been distinguished
by the establishment of the theory of definite proportions, and by
discoveries which pointed to the electro-chemical theory, it could
not appear presumption to suppose, that the classification of
bodies, so far as it depended on chemistry, might be presented in a
form more complete and scientific than at any previous time.
The attempt to do this was made by the great Swedish chemist Jacob
Berzelius. In 1816, he published his _Essay to establish a purely
Scientific System of Mineralogy, by means of the Application of the
Electro-chemical Theory and the Chemical Doctrine of Definite
Proportions_. It is manifest that, for minerals which are
constituted by the law of Definite Proportions, this constitution
must be a most essential part of their character. The
electro-chemical theory was called in aid, in addition to the
composition, because, distinguishing the elements of all compounds
as electro-positive and electro-negative, and giving to every
element a place in a series, and a place defined by the degree of
these relations, it seemed to afford a rigorous and complete
principle of arrangement. Accordingly, Berzelius, in his First
System, arranged minerals according to their electro-positive
element, and the elements according to their electro-positive rank;
{348} and supposed that he had thus removed all that was arbitrary
and vague in the previous chemical systems of mineralogy.
Though the attempt appeared so well justified by the state of
chemical science, and was so plausible in its principle, it was not
long before events showed that there was some fallacy in these
specious appearances. In 1820, Mitscherlich discovered Isomorphism:
by that discovery it appeared that bodies containing very different
electro-positive elements could not be distinguished from each
other; it was impossible, therefore, to put them in distant portions
of the classification;--and thus the first system of Berzelius
crumbled to pieces.
But Berzelius did not so easily resign his project. With the most
unhesitating confession of his first failure, but with undaunted
courage, he again girded himself to the task of rebuilding his
edifice. Defeated at the electro-positive position, he now resolved
to make a stand at the electro-negative element. In 1824, he
published in the Transactions of the Swedish Academy, a Memoir _On
the Alterations in the Chemical Mineral System, which necessarily
follow from the Property exhibited by Isomorphous Bodies, of
replacing each other in given Proportions_. The alteration was, in
fact, an inversion of the system, with an attempt still to preserve
the electro-chemical principle of arrangement. Thus, instead of
arranging metallic minerals according to the _metal_, under iron,
copper, &c., all the _sulphurets_ were classed together, all the
_oxides_ together, all the _sulphates_ together, and so in other
respects. That such an order was a great improvement on the
preceding one, cannot be doubted; but we shall see, I think, that as
a strict scientific system it was not successful. The discovery of
isomorphism, however, naturally led to such attempts. Thus Gmelin
also, in 1825, published a mineral system,[50\15] which, like that
of Berzelius, founded its leading distinctions on the
electro-negative, or, as it was sometimes termed, the _formative_
element of bodies; and, besides this, took account of the _numbers_
of atoms or proportions which appear in the composition of the body;
distinguishing, for instance, Silicates, as simple silicates, double
silicates, and so on, to _quintuple_ silicate (_Pechstein_) and
_sextuple_ silicate (_Perlstein_). In like manner, Nordenskiöld
devised a system resting on the same bases, taking into account also
the crystalline form. In 1824, Beudant published his _Traité
Elémentaire de Minéralogie_, in which he professes to found his
arrangement on the electro-negative element, and on Ampère's
circular {349} arrangement of elementary substances. Such schemes
exhibit rather a play of the mere logical faculty, exercising itself
on assumed principles, than any attempt at the real interpretation
of nature. Other such pure chemical systems may have been published,
but it is not necessary to accumulate instances. I proceed to
consider their result.
[Note 50\15: _Zeitsch. der Min._ 1825, p. 435.]
_Sect._ 3.--_Failure of the Attempts at Systematic Reform._
IT may appear presumptuous to speak of the failure of those whom,
like Berzelius and Mohs, we acknowledge as our masters, at a period
when, probably, they and some of their admirers still hold them to
have succeeded in their attempt to construct a consistent system.
But I conceive that my office as an historian requires me to exhibit
the fortunes of this science in the most distinct form of which they
admit, and that I cannot evade the duty of attempting to seize the
true aspect of recent occurrences in the world of science. Hence I
venture to speak of the failure of both the attempts at framing a
pure scientific system of mineralogy,--that founded on the chemical,
and that founded on the natural-history principle; because it is
clear that they have not obtained that which alone we could,
according to the views here presented, consider as success,--a
coincidence of each with the other. A Chemical System of
arrangement, which should bring together, in all cases, the
substances which come nearest each other in external properties;--a
Natural-history System, which should be found to arrange bodies in
complete accordance with their chemical constitution:--if such
systems existed, they might, with justice, claim to have succeeded.
Their agreement would be their verification. The interior and
exterior system are the type and the antitype, and their entire
correspondence would establish the mode of interpretation beyond
doubt. But nothing less than this will satisfy the requisitions of
science. And when, therefore, the chemical and the natural-history
system, though evidently, as I conceive, tending towards each other,
are still far from coming together, it is impossible to allow that
either method has been successful in regard to its proper object.
But we may, I think, point out the fallacy of the principles, as well
as the imperfection of the results, of both of those methods. With
regard to that of Berzelius, indeed, the history of the subject
obviously betrays its unsoundness. The electro-positive principle was,
in a very short time after its adoption, proved and acknowledged to be
utterly untenable: what security have we that the electro-negative
element is {350} more trustworthy? Was not the necessity of an entire
change of system, a proof that the ground, whatever that was, on which
the electro-chemical principle was adopted, was an unfounded
assumption? And, in fact, do we not find that the same argument which
was allowed to be fatal to the First System of Berzelius, applies in
exactly the same manner against the Second? If the electro-positive
elements be often isomorphous, are not the electro-negative elements
sometimes isomorphous also? for instance, the arsenic and phosphoric
acids. But to go further, what _is_ the ground on which the
electro-chemical arrangement is adopted? Granted that the electrical
relations of bodies are important; but how do we come to know that
these relations have anything to do with mineralogy? How does it
appear that on them, principally, depend those external properties
which mineralogy must study? How does it appear that because sulphur
is the electro-negative part of one body, and an acid the
electro-negative part of another, these two elements similarly affect
the compounds? How does it appear that there is any analogy whatever
in their functions? We allow that the composition must, in _some way_,
determine the classified place of the mineral,--but why in _this_ way?
I do not dwell on the remark which Berzelius himself[51\15] makes on
Nordenskiöld's system;--that it assumes a perfect knowledge of the
composition in every case; although, considering the usual
discrepancies of analyses of minerals, this objection must make all
pure chemical systems useless. But I may observe, that mineralogists
have not yet determined what characters are sufficiently affixed to
determine a species of minerals. We have seen that the ancient
notion of the composition of a species, has been unsettled by the
discovery of isomorphism. The tenet of the constancy of the angle is
rendered doubtful by cases of plesiomorphism. The optical
properties, which are so closely connected with the crystalline, are
still so imperfectly known, that they are subject to changes which
appear capricious and arbitrary. Both the chemical and the optical
mineralogists have constantly, of late, found occasion to separate
species which had been united, and to bring together those which had
been divided. Everything shows that, in this science, we have our
classification still to begin. The detection of that fixity of
characters, on which a right establishment of species must rest, is
not yet complete, great as the progress is which we have made, by
acquiring a knowledge of the laws of crystallization and of {351}
definite chemical constitution. Our ignorance may surprise us; but
it may diminish our surprise to recollect, that the knowledge which
we seek is that of the laws of the physical constitution of all
bodies whatever; for to us, as mineralogists, all chemical compounds
are minerals.
[Note 51\15: _Jahres Bericht._ viii. 188.]
The defect of the principle of the natural-history classifiers may be
thus stated:--in studying the external characters of bodies, they take
for granted that they can, without any other light, discover the
relative value and importance of those characters. The grouping of
Species into a Genus, of Genera into an Order, according to the method
of this school, proceeds by no definite rules, but by a latent talent
of appreciation,--a sort of classifying instinct. But this course
cannot reasonably be expected to lead to scientific truth; for it can
hardly be hoped, by any one who looks at the general course of
science, that we shall discover the relation between external
characters and chemical composition, otherwise than by tracing their
association in cases where both are known. It is urged that in other
classificatory sciences, in botany, for example, we obtain a natural
classification from external characters without having recourse to any
other source of knowledge. But this is not true in the sense here
meant. In framing a natural system of botany, we have constantly
before our eyes the principles of physiology; and we estimate the
value of the characters of a plant by their bearing on its
functions,--by their place in its organization. In an unorganic body,
the chemical constitution is the law of its being; and we shall never
succeed in framing a science of such bodies but by studiously
directing our efforts to the interpretation of that law.
On these grounds, then, I conceive, that the bold attempts of Mohs
and of Berzelius to give new forms to mineralogy, cannot be deemed
successful in the manner in which their authors aspired to succeed.
Neither of them can be marked as a permanent reformation of the
science. I shall not inquire how far they have been accepted by men
of science, for I conceive that their greatest effect has been to
point out improvements which might be made in mineralogy without
going the whole length either of the _pure_ chemical, or of the
_pure_ natural-history system.
_Sect._ 4.--_Return to Mixed Systems with Improvements._
IN spite of the efforts of the purists, mineralogists returned to
mixed systems of classification; but these systems are much better
than they were before such efforts were made. {352}
The Second System of Berzelius, though not tenable in its rigorous
form, approaches far nearer than any previous system to a complete
character, bringing together like substances in a large portion of
its extent. The System of Mohs also, whether or not unconsciously
swayed by chemical doctrines, forms orders which have a community of
chemical character; thus, the minerals of the order _Haloide_ are
salts of oxides, and those of the order _Pyrites_ are sulphurets of
metals. Thus the two methods appear to be converging to a common
centre; and though we are unable to follow either of them to this
point of union, we may learn from both in what direction we are to
look for it. If we regard the best of the pure systems hitherto
devised as indications of the nature of that system, perfect both as
a chemical and as a natural-history system, to which a more complete
condition of mineralogical knowledge may lead us, we may obtain,
even at present, a tolerably good approximation to a complete
classification; and such a one, if we recollect that it must be
imperfect, and is to be held as provisional only, may be of no small
value and use to us.
The best of the mixed systems produced by this compromise again
comes from Freiberg, and was published by Professor Naumann in 1828.
Most of his orders have both a chemical character and great external
resemblances. Thus his _Haloides_, divided into _Unmetallic_ and
_Metallic_, and these again into _Hydrous_ and _Anhydrous_, give
good natural groups. The most difficult minerals to arrange in all
systems are the siliceous ones. These M. Naumann calls _Silicides_,
and subdivides them into _Metallic_, _Unmetallic_, and _Amphoteric_
or mixed; and again, into _Hydrous_ and _Anhydrous_. Such a system
is at least a good basis for future researches; and this is, as we
have said, all that we can at present hope for. And when we
recollect that the natural-history principle of classification has
begun, as we have already seen, to make its appearance in our
treatises of chemistry, we cannot doubt that some progress is making
towards the object which I have pointed out. But we know not yet how
far we are from the end. The combination of chemical,
crystallographical, physical and optical properties into some lofty
generalization, is probably a triumph reserved for future and
distant years.
_Conclusion._--The history of Mineralogy, both in its successes and
by its failures, teaches us this lesson;--that in the sciences of
classification, the establishment of the fixity of characters, and
the discovery of such characters as are fixed, are steps of the
first importance in the progress of these sciences. The recollection
of this maxim may aid us in {353} shaping our course through the
history of other sciences of this kind; in which, from the extent of
the subject, and the mass of literature belonging to it, we might at
first almost despair of casting the history into distinct epochs and
periods. To the most prominent of such sciences, Botany, I now
proceed.
{{355}}
BOOK XVI.
_CLASSIFICATORY SCIENCES._
HISTORY
OF
SYSTEMATIC BOTANY AND ZOOLOGY.
. . . . . Vatem aspicies quæ rupe sub altâ
Fata canit, foliisque notas et nomina mandat.
Quæcunque in foliis descripsit carmina virgo
Digerit in numerum atque antro seclusa relinquit
Illa manent immorta locis neque ab ordine cedunt.
VIRGIL. _Æn._ iii. 443.
Behold the Sibyl!--Her who weaves a long,
A tangled, full, yet sweetly flowing song.
Wondrous her skill; for leaf on leaf she frames
Unerring symbols and enduring names;
And as her nicely measured line she binds,
For leaf on leaf a fitting place she finds;
Their place once found, no more the leaves depart,
But fixed rest:--such is her magic art.
{{357}}
INTRODUCTION.
WE now arrive at that study which offers the most copious and
complete example of the sciences of classification, I mean Botany.
And in this case, we have before us a branch of knowledge of which
we may say, more properly than of any of the sciences which we have
reviewed since Astronomy, that it has been constantly advancing,
more or less rapidly, from the infancy of the human race to the
present day. One of the reasons of this resemblance in the fortunes
of two studies so widely dissimilar, is to be found in a simplicity
of principle which they have in common; the ideas of Likeness and
Difference, on which the knowledge of plants depends, are, like the
ideas of Space and Time, which are the foundation of astronomy,
readily apprehended with clearness and precision, even without any
peculiar culture of the intellect. But another reason why, in the
history of Botany, as in that of Astronomy, the progress of
knowledge forms an unbroken line from the earliest times, is
precisely the great difference of the kind of knowledge which has
been attained in the two cases. In Astronomy, the discovery of
general truths began at an early period of civilization; in Botany,
it has hardly yet begun; and thus, in each of these departments of
study, the lore of the ancient is homogeneous with that of the
modern times, though in the one case it is science, in the other,
the absence of science, which pervades all ages. The resemblance of
the form of their history arises from the diversity of their
materials.
I shall not here dwell further upon this subject, but proceed to
trace rapidly the progress of _Systematic Botany_, as the
classificatory science is usually denominated, when it is requisite
to distinguish between that and Physiological Botany. My own
imperfect acquaintance with this study admonishes me not to venture
into its details, further than my purpose absolutely requires. I
trust that, by taking my views principally from writers who are
generally allowed to possess the best insight into the science, I
may be able to draw the larger features of its history with
tolerable correctness; and if I succeed in this, I shall attain an
object of great importance in my general scheme. {358}
CHAPTER I.
IMAGINARY KNOWLEDGE OF PLANTS.
THE apprehension of such differences and resemblances as those by
which we group together and discriminate the various kinds of plants
and animals, and the appropriation of words to mark and convey the
resulting notions, must be presupposed, as essential to the very
beginning of human knowledge. In whatever manner we imagine man to
be placed on the earth by his Creator, these processes must be
conceived to be, as our Scriptures represent them, contemporaneous
with the first exertion of reason, and the first use of speech. If
we were to indulge ourselves in framing a hypothetical account of
the origin of language, we should probably assume as the
first-formed words, those which depend on the visible likeness or
unlikeness of objects; and should arrange as of subsequent
formation, those terms which imply, in the mind, acts of wider
combination and higher abstraction. At any rate, it is certain that
the names of the kinds of vegetables and animals are very abundant
even in the most uncivilized stages of man's career. Thus we are
informed[1\16] that the inhabitants of New Zealand have a distinct
name of every tree and plant in their island, of which there are six
or seven hundred or more different kinds. In the accounts of the
rudest tribes, in the earliest legends, poetry, and literature of
nations, pines and oaks, roses and violets, the olive and the vine,
and the thousand other productions of the earth, have a place, and
are spoken of in a manner which assumes, that in such kinds of
natural objects, permanent and infallible distinctions had been
observed and universally recognized.
[Note 1\16: Yate's _New Zealand_, p. 238.]
For a long period, it was not suspected that any ambiguity or
confusion could arise from the use of such terms; and when such
inconveniences did occur, (as even in early times they did,) men
were far from divining that the proper remedy was the construction
of a science of classification. The loose and insecure terms of the
language of common life retained their place in botany, long after
their {359} defects were severely felt: for instance, the vague and
unscientific distinction of vegetables into _trees_, _shrubs_, and
_herbs_, kept its ground till the time of Linnæus.
While it was thus imagined that the identification of a plant, by
means of its name, might properly be trusted to the common
uncultured faculties of the mind, and to what we may call the
instinct of language, all the attention and study which were
bestowed on such objects, were naturally employed in learning and
thinking upon such circumstances respecting them as were supplied by
any of the common channels through which knowledge and opinion flow
into men's minds.
The reader need hardly be reminded that in the earlier periods of
man's mental culture, he acquires those opinions on which he loves
to dwell, not by the exercise of observation subordinate to reason;
but, far more, by his fancy and his emotions, his love of the
marvellous, his hopes and fears. It cannot surprise us, therefore,
that the earliest lore concerning plants which we discover in the
records of the past, consists of mythological legends, marvellous
relations, and extraordinary medicinal qualities. To the lively
fancy of the Greeks, the Narcissus, which bends its head over the
stream, was originally a youth who in such an attitude became
enamored of his own beauty: the hyacinth,[2\16] on whose petals the
notes of grief were traced (A I, A I), recorded the sorrow of Apollo
for the death of his favorite Hyacinthus: the beautiful lotus of
India,[3\16] which floats with its splendid flower on the surface of
the water, is the chosen seat of the goddess Lackshmi, the daughter
of Ocean.[4\16] In Egypt, too,[5\16] Osiris swam on a lotus-leaf and
Harpocrates was cradled in one. The lotus-eaters of Homer lost
immediately their love of home. Every one knows how easy it would be
to accumulate such tales of wonder or religion.
[Note 2\16: Lilium martagon.
Ipse suos gemitus foliis inscribit et A I, A I,
Flos habet inscriptum funestaque litera ducta est.--OVID.]
[Note 3\16: Nelumbium speciosum.]
[Note 4\16: Sprengel, _Geschichte der Botanik_, i. 27.]
[Note 5\16: Ib. i. 28.]
Those who attended to the effects of plants, might discover in them
some medicinal properties, and might easily imagine more; and when
the love of the marvellous was added to the hope of health, it is
easy to believe that men would be very credulous. We need not dwell
upon the examples of this. In Pliny's Introduction to that book of
his {360} Natural History which treats of the medicinal virtues of
plants, he says,[6\16] "Antiquity was so much struck with the
properties of herbs, that it affirmed things incredible. Xanthus,
the historian, says, that a man killed by a dragon, will be restored
to life by an herb which he calls _balin_; and that Thylo, when
killed by a dragon, was recovered by the same plant. Democritus
asserted, and Theophrastus believed, that there was an herb, at the
touch of which, the wedge which the woodman had driven into a tree
would leap out again. Though we cannot credit these stories, most
persons believe that almost anything might be effected by means of
herbs, if their virtues were fully known." How far from a reasonable
estimate of the reality of such virtues were the persons who
entertained this belief we may judge from the many superstitious
observances which they associated with the gathering and using of
medicinal plants. Theophrastus speaks of these;[7\16] "The
drug-sellers and the rhizotomists (root-cutters) tell us," he says,
"some things which may be true, but other things which are merely
solemn quackery;[8\16] thus they direct us to gather some plants,
standing from the wind, and with our bodies anointed; some by night,
some by day, some before the sun falls on them. So far there may be
something in their rules. But others are too fantastical and far
fetched. It is, perhaps, not absurd to use a prayer in plucking a
plant; but they go further than this. We are to draw a sword three
times round the mandragora, and to cut it looking to the west:
again, to dance round it, and to use obscene language, as they say
those who sow cumin should utter blasphemies. Again, we are to draw
a line round the black hellebore, standing to the east and praying;
and to avoid an eagle either on the right or on the left; for, say
they, 'if an eagle be near, the cutter will die in a year.'"
[Note 6\16: Lib. xxv. 5.]
[Note 7\16: _De Plantis_, ix. 9.]
[Note 8\16: Ἐπιτραγῳδοῦντες.]
This extract may serve to show the extent to which these
imaginations were prevalent, and the manner in which they were
looked upon by Theophrastus, our first great botanical author. And
we may now consider that we have given sufficient attention to these
fables and superstitions, which have no place in the history of the
progress of real knowledge, except to show the strange chaos of wild
fancies and legends out of which it had to emerge. We proceed to
trace the history of the knowledge of plants. {361}
CHAPTER II.
UNSYSTEMATIC KNOWLEDGE OF PLANTS.
A STEP was made towards the formation of the Science of Plants,
although undoubtedly a slight one, as soon as men began to collect
information concerning them and their properties, from a love and
reverence for knowledge, independent of the passion for the
marvellous and the impulse of practical utility. This step was very
early made. The "wisdom" of Solomon, and the admiration which was
bestowed upon it, prove, even at that period, such a working of the
speculative faculty: and we are told, that among other evidences of
his being "wiser than all men," "he spake of trees, from the
cedar-tree that is in Lebanon even unto the hyssop that springeth
out of the wall."[9\16] The father of history, Herodotus, shows us
that a taste for natural history had, in his time, found a place in
the minds of the Greeks. In speaking of the luxuriant vegetation of
the Babylonian plain,[10\16] he is so far from desiring to astonish
merely, that he says, "the blades of wheat and barley are full four
fingers wide; but as to the size of the trees which grow from millet
and sesame, though I could mention it, I will not; knowing well that
those who have not been in that country will hardly believe what I
have said already." He then proceeds to describe some remarkable
circumstances respecting the fertilization of the date-palms in
Assyria.
[Note 9\16: 1 Kings iv. 33.]
[Note 10\16: Herod. i. 193.]
This curious and active spirit of the Greeks led rapidly, as we have
seen in other instances, to attempts at collecting and systematizing
knowledge on almost every subject: and in this, as in almost every
other department, Aristotle may be fixed upon, as the representative
of the highest stage of knowledge and system which they ever
attained. The vegetable kingdom, like every other province of
nature, was one of the fields of the labors of this universal
philosopher. But though his other works on natural history have come
down to us, and are a most valuable monument of the state of such
knowledge in his time, his Treatise on Plants is lost. The book _De
Plantis_ {362} which appears with his name, is an imposture of the
middle ages, full of errors and absurdities.[11\16]
[Note 11\16: Mirbel, _Botanique_, ii. 505.]
His disciple, friend, and successor, Theophrastus of Eresos, is, as
we have said already, the first great writer on botany whose works
we possess; and, as may be said in most cases of the first great
writer, he offers to us a richer store of genuine knowledge and good
sense than all his successors. But we find in him that the Greeks of
his time, who aspired, as we have said, to collect and _systematize_
a body of information on every subject, failed in one half of their
object, as far as related to the vegetable world. Their attempts at
a systematic distribution of plants were altogether futile. Although
Aristotle's divisions of the animal kingdom are, even at this day,
looked upon with admiration by the best naturalists, the
arrangements and comparisons of plants which were contrived by
Theophrastus and his successors, have not left the slightest trace
in the modern form of the science; and, therefore, according to our
plan, are of no importance in our history. And thus we can treat all
the miscellaneous information concerning vegetables which was
accumulated by the whole of this school of writers, in no other way
than as something antecedent to the first progress towards
systematic knowledge.
The information thus collected by the unsystematic writers is of
various kinds; and relates to the economical and medicinal uses of
plants, their habits, mode of cultivation, and many other
circumstances: it frequently includes some description; but this is
always extremely imperfect, because the essential conditions of
description had not been discovered. Of works composed of materials
so heterogeneous, it can be of little use to produce specimens; but
I may quote a few words from Theophrastus, which may serve to
connect him with the future history of the science, as bearing upon
one of the many problems respecting the identification of ancient
and modern plants. It has been made a question whether the following
description does not refer to the potato.[12\16] He is speaking of
the differences of roots: "Some roots," he says, "are still
different from those which have been described; as that of the
_arachidna_[13\16] plant: for this bears fruit underground as well
as above: the fleshy part sends one thick root deep into the ground,
but the others, which bear the fruit, are more slender {363} and
higher up, and ramified. It loves a sandy soil, and has no leaf
whatever."
[Note 12\16: Theoph. i. 11.]
[Note 13\16: Most probably the _Arachnis hypogæa_, or ground-nut.]
The books of Aristotle and Theophrastus soon took the place of the
Book of Nature in the attention of the degenerate philosophers who
succeeded them. A story is told by Strabo[14\16] concerning the fate
of the works of these great naturalists. In the case of the wars and
changes which occurred among the successors of Alexander, the heirs
of Theophrastus tried to secure to themselves his books, and those
of his master, by burying them in the ground. There the manuscripts
suffered much from damp and worms; till Apollonicon, a
book-collector of those days, purchased them, and attempted, in his
own way, to supply what time had obliterated. When Sylla marched the
Roman troops into Athens, he took possession of the library of
Apollonicon; and the works which it contained were soon circulated
among the learned of Rome and Alexandria, who were thus enabled to
_Aristotelize_[15\16] on botany as on other subjects.
[Note 14\16: Strabo, lib. xiii. c. i. § 54.]
[Note 15\16: Ἀριστοτλίζειν.]
The library collected by the Attalic kings of Pergamus, and the
Alexandrian Museum, founded and supported by the Ptolemies of Egypt,
rather fostered the commentatorial spirit than promoted the increase
of any real knowledge of nature. The Romans, in this as in other
subjects, were practical, not speculative. They had, in the times of
their national vigor, several writers on agriculture, who were
highly esteemed; but no author, till we come to Pliny, who dwells on
the mere knowledge of plants. And even in Pliny, it is easy to
perceive that we have before us a writer who extracted his
information principally from books. This remarkable man,[16\16] in
the middle of a public and active life, of campaigns and voyages,
contrived to accumulate, by reading and study, an extraordinary
store of knowledge of all kinds. So unwilling was he to have his
reading and note-making interrupted, that, even before day-break in
winter, and from his litter as he travelled, he was wont to dictate
to his amanuensis, who was obliged to preserve his hand from the
numbness which the cold occasioned, by the use of gloves.[17\16]
[Note 16\16: Sprengel, i. 163.]
[Note 17\16: Plin. Jun. Epist. 3, 5.]
It has been ingeniously observed, that we may find traces in the
botanical part of his Natural History, of the errors which this
hurried and broken habit of study produced; and that he appears
frequently to have had books read to him and to have heard them
amiss.[18\16] Thus, {364} among several other instances,
Theophrastus having said that the plane-tree is in Italy
rare,[19\16] Pliny, misled by the similarity of the Greek word
(_spanian_, rare), says that the tree occurs in Italy and
Spain.[20\16] His work has, with great propriety, been called the
Encyclopædia of Antiquity; and, in truth, there are few portions of
the learning of the times to which it does not refer. Of the
thirty-seven Books of which it consists, no less than sixteen (from
the twelfth to the twenty-seventh) relate to plants. The information
which is collected in these books, is of the most miscellaneous
kind; and the author admits, with little distinction, truth and
error, useful knowledge and absurd fables. The declamatory style,
and the comprehensive and lofty tone of thought which we have
already spoken of as characteristic of the Roman writers, are
peculiarly observable in him. The manner of his death is well known:
it was occasioned by the eruption of Vesuvius, A.D. 79, to which, in
his curiosity, he ventured so near as to be suffocated.
[Note 18\16: Sprengel, i. 163.]
[Note 19\16: Theoph. iv. 7. Ἔν μὲν γὰρ τῷ Ἀδρίᾳ πλάτανον οὐ φασὶν
εἶναι πλῆν περὶ το Διομήδους ἱερόν, _σπανίαν_ δὲ καὶ ἐν Ἰταλίᾳ πάσῃ]
[Note 20\16: Plin. Nat. Hist. xii. 3. Et alias (platanos) fuisse in
Italia, ac nominatim _Hispania_, apud auctores invenitur.]
Pliny's work acquired an almost unlimited authority, as one of the
standards of botanical knowledge, in the middle ages; but even more
than his, that of his contemporary, Pedanius Dioscorides, of
Anazarbus in Cilicia. This work, written in Greek, is held by the
best judges[21\16] to offer no evidence that the author observed for
himself. Yet he says expressly in his Preface, that his love of
natural history, and his military life, have led him into many
countries, in which he has had opportunity to become acquainted with
the nature of herbs and trees.[22\16] He speaks of six hundred
plants, but often indicates only their names and properties, giving
no description by which they can be identified. The main cause of
his great reputation in subsequent times was, that he says much of
the medicinal virtues of vegetables.
[Note 21\16: Mirbel, 510.]
[Note 22\16: Sprengel, i. 136.]
We come now to the ages of darkness and lethargy, when the habit of
original thought seems to die away, as the talent of original
observation had done before. Commentators and mystics succeed to the
philosophical naturalists of better times. And though a new race,
altogether distinct in blood and character from the Greek,
appropriates to itself the stores of Grecian learning, this movement
does not, as might be expected, break the chains of literary
slavery. The Arabs {365} bring, to the cultivation of the science of
the Greeks, their own oriental habit of submission, their oriental
love of wonder; and thus, while they swell the herd of commentators
and mystics, they produce no philosopher.