BOOK XV.

MINERALOGY.

BY the kindness of W. H. Miller, Esq., Professor of Mineralogy in

the University of Cambridge, I am able to add to this part the following notices of books and memoirs.

1. Crystallography.

2.

Elemente der Krystallographie, nebst einer tabellarischen Uebersicht der Mineralien nach der Krystallformen, von Gustav Rose. Auflage. Berlin, 1838. The crystallographic method here adopted is, for the most part, that of Weiss. The method of this work has been followed in

A System of Crystallography, with its Applications to Mineralogy. By John Joseph Griffin. Glasgow, 1841. Mr. Griffin has, however, modified the notation of Rose. He has constructed a series of models of crystalline forms.

Frankenheim's System der Krystalle. 1842. This work adopts nearly the Mohsian systems of crystallization. It contains Tables of the chemical constitution, inclinations of the axis, and magnitude of the axes of all the crystals of which a description was to be found, including those formed in the laboratory, as well as those usually called minerals; 713 in all.

Fr. Aug. Quenstedt, Methode der Krystallographie, 1840, employs a fanciful method of representing a crystal by projecting upon one face of the crystal all the other faces. This invention appears to be more curious than useful.

Dr. Karl Naumann, who is spoken of in Chap ix. of this Book, as the author of the best of the Mixed Systems of Classification, published also Grundriss der Krystallographie. Leipzig, 1826. In this and other works he modifies the notation of Mohs in a very advantageous

manner.

Professor Dana, in his System of Mineralogy, New Haven (U.S.A. 1837, follows Naumann for the most part, both in crystallography and in mineral classification. In the latter part of the subject, he has made the attempt, which in all cases is a source of confusion and of failure, to introduce a whole system of new names of the members of his classification.

The geometry of crystallography has been investigated in a very original manner by M. Bravais, in papers published in the Journal of the Ecole Polytechnique, entitled Mémoires sur les Systèmes formés par des Points. 1850. Etudes Crystallographiques. 1851.

Hermann Kopp (Einleitung in die Krystallographie, Braunschweig. 1849) has given the description and measurement of the angles of a large number of laboratory crystals.

Rammelsberg (Krystallographische Chemie, Berlin, 1855) has collected an account of the systems, simple forms and angles of all the laboratory crystals of which he could obtain descriptions.

Schabus of Vienna (Bestimmung der Krystallgestalten in Chemischen Laboratorien erzeugten Producte, Wien, 1855; a successful Prize Essay) has given a description, accompanied by measurements, of 90 crystalline species from his own observations.

To these attempts made in other countries to simplify and improve crystallography, I may add a remarkable Essay very recently made here by Mr. Brooke, and suggested to him by his exact and familiar knowledge of Mineralogy. It is to this effect. All the crystalline forms of any given mineral species are derived from the primitive form of that species; and the degree of symmetry, and the parameters, of this form determine the angles of all derivative forms. But how is this primitive form selected and its parameters determined? The selection of the kind of the primitive form depends upon the degree of symmetry which appears in all the derivative forms; according to which they belong to the rhombohedral, prismatic, square pyramidal, or some other system and this determination is commonly clear. But the parameters, or the angles, of the primitive form, are commonly determined by the cleavage of the mineral. Is this a sufficient and necessary ground of such determination? May not a simplification be effected, in some cases, by taking some other parameters? by taking a primitive form which belongs to the proper system, but which has some other angles than those given by cleavage? Mr. Brooke has tried whether, for instance, crystals of the rhombohedral system may not be referred with advantage to primitive rhombohedrons which have, in all

the species, nearly the same angles. The advantage to be obtained by such a change would be the simplification of the laws of derivation in the derivative forms: and therefore we have to ask, whether the indices of derivation are smaller numbers in this way or with the hitherto accepted fundamental angles. It appears to me, from the examples given, that the advantage of simplicity in the indices is on the side of the old system: but whether this be so or not, it was a great benefit to crystallography to have the two methods compared. Mr. Brooke's Essay is a Memoir presented to the Royal Society in 1856.

2. Optical Properties of Minerals.

The Handbuch der Optik, von F. W. G. Radicke, Berlin, 1839, contains a chapter on the optical properties of crystals. The author's chief authority is Sir D. Brewster, as might be expected.

M. Haidinger has devoted much attention to experiments on the pleochroism of minerals. He has invented an instrument which makes the dichroism of minerals more evident by exhibiting the two colors side by side.

The pleochroism of minerals, and especially the remarkable clouds. that in the cases of Iolite, Andalusite, Augite, Epidote, and Axinite, border the positions of either optical axis, have been most successfully imitated by M. de Senarmont by means of artificial crystallizations. (Ann. de Chim. 3 Ser. xli. p. 319.)

M. Pasteur has found that Racemic Acid consists of two different acids, having the same density and composition. The salts of these acids, with bases of Ammonia and of Potassa, are hemihedral, the hemihedral faces which occur in the one being wanting in the other. The acids of these different crystals have circular polarization of opposite kinds. (Ann. de Chim. 3 Ser. xxviii. 56, 99.) This discovery was marked by the assignation of the Rumford Medal to M. Pasteur

in 1856.

M. Marbach has discovered that crystals of chlorate of soda, which apparently belongs to the cubic or tessular system, exhibit hemihedral faces of a peculiar character; and that the crystals have circular polarization of opposite kinds in accordance with the differences of the plagihedral faces. (Poggendorf's Annalen, xci. 482.)

M. Seybolt of Vienna has found a means of detecting plagihedral faces in quartz crystals which do not reveal them externally. (Akad. d. Wissenschaft zu Wien, B. xv. s. 59.)

3. Classification of Minerals.

In the Philosophy of the Inductive Sciences, B. VIII. C. iii., I have treated of the Application of the Natural-history Method of Classification to Mineralogy, and have spoken of the Systems of this kind which have been proposed. I have there especially discussed the system proposed in the treatise of M. Necker, Le Règne Mineral ramené aux Méthodes d'Histoire Naturelle (Paris, 1835). More recently have been published M. Beudant's Cours élémentaire d'Histoire Naturelle, Minéralogie (Paris, 1841); and M. A. Dufresnoy's Traité de Minéralogie (Paris, 1845). Both these works are so far governed by mere chemical views that they lapse into the inconveniences and defects which are avoided in the best systems of German mineralogists.

The last mineral system of Berzelius has been developed by M. Rammelsberg (Nürnberg, 1847). It is in principle such as we have described it in the history.

M. Nordenskiold's system (3rd Ed. 1849,) has been criticised by G. Rose, who observes that it removes the defects of the system of Berzelius only in part. He himself proposes what he calls a "KrystalloChemisches System," in which the crystalline form determines the genus and the chemical composition the species. His classes are1. Simple Substances.

2. Combinations of Sulphur, Selenium, Titanium, Arsenic, Antimony. 3. Chlorides, Fluorides, Bromides, Iodides.

4. Combinations with Oxygen.

We have already said that for us, all chemical compounds are minerals, in so far that they are included in our classifications. The propriety of this mode of dealing with the subject is confirmed by our finding that there is really no tenable distinction between native minerals and the products of the laboratory. A great number of eminent chemists have been employed in producing, by artificial means, crystals which had before been known only as native products.

BOOK XVI.

CLASSIFICATORY SCIENCES.

FOR

BOTANY.

OR the purpose of giving to my reader some indication of the present tendency of Botanical Science, I conceive that I cannot do better than direct his attention to the reflections, procedure, and reasonings which have been suggested by the most recent extensions of man's knowledge of the vegetable world. And as a specimen of these, I may take the labors of Dr. Joseph Hooker, on the Flora of the Antarctic Regions,' and especially of New Zealand. Dr. Hooker was the Botanist to an expedition commanded by Sir James Ross, sent out mainly for the purpose of investigating the phenomena of Terrestrial Magnetism near the South Pole; but directed also to the improvement of Natural History. The extension of botanical descriptions and classifications to a large mass of new objects necessarily suggests wider views of the value of classes (genera, species, &c.,) and the conclusions to be drawn from their constancy or inconstancy. A few of Dr. Hooker's remarks may show the nature of the views taken under such circumstances.

I may notice, in the first place, (since this work is intended for general rather than for scientific readers,) Dr. Hooker's testimony to the value of a technical descriptive language for a classificatory sciencea Terminology, as it is called. He says, "It is impossible to write Botanical descriptions which a person ignorant of Botany can understand, although it is supposed by many unacquainted with science that this can and should be done." And hence, he says, the state of botanical science demands Latin descriptions of the plants; and this is a lesson which he especially urges upon the Colonists who study the indigenous plants.

1 The Botany of the Antarctic Voyage of H. M. Discovery Ships Erebus and Terror, in the years 1839-40. Published 1847. Flora Nova Zelandia. 1853.