CHAPTER IX

.

THE ELECTRO-CHEMICAL THEORY.

AMONG the consequences of the Electro-chemical Theory, must be ranged the various improvements which have been made in the voltaic battery. Daniel introduced between the two metals a partition permeable by chemical action, but such as to allow of two different acid solutions being in contact with the two metals. Mr. Grove's battery, in which the partition is of porous porcelain, and the metals are platinum and amalgamated zinc, is one of the most powerful hitherto known. Another has been constructed by Dr. Callan, in which the negative or conducting plate is a cylinder of cast iron, and the positive element a cylinder of amalgamated zinc placed in a porous cell. This also has great energy.

_The Number of Elementary Substances._

There have not been, I believe, any well-established additions to the list of the simple substances recognized by chemists. Indeed the tendency at present appears to be rather to deny the separate elementary character of some already announced as such substances. Pelopium and Niobium were, as I have said, two of the new metals. But Naumann, in his _Elemente der Mineralogie_ (4th ed. 1855), says, in a foot note (page 25): "_Pelopium_ is happily again got rid of; for Pelopic Acid and Niobic Acid possess the same Radical. _Donarium_ had a still shorter existence."

In the same way, when Hermann imagined that he had discovered a new simple metallic substance in the mineral Samarskite from Miask, the discovery was disproved by H. Rose (_Pogg. Ann._ B. 73, s. 449). {626}

In general the insulation of the new simple substances, the metallic bases of the earths, and the like,--their separation from their combinations, and the exhibition of them in a metallic form--has been a difficult chemical process, and has rarely been executed on any considerable scale. But in the case of _Aluminium_, the basis of the earth Alumina, the process of its extraction has recently been so much facilitated, that the metal can be produced in abundance. This being the case, it will probably soon be applied to special economical uses, for which it is fitted by possessing special properties.

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## 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._

_Elemente der Krystallographie, nebst einer tabellarischen Uebersicht der Mineralien nach der Krystallformen_, von Gustav Rose. 2. 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. {628}

Professor Dana, in his _System of Mineralogy_, New Haven (U.S.), 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 {629} 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.) {630}

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 Minéral 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. **Nordenskiöld'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 "Krystallo-Chemisches System," in which the crystalline form determines the genus and the chemical composition the species. His classes are-- 1. 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.

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## BOOK XVI.

CLASSIFICATORY SCIENCES.

BOTANY.

FOR 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,[41\B] 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.

[Note 41\B: _The Botany of the Antarctic Voyage of H. M. Discovery Ships Erebus and Terror, in the years_ 1839-40. Published 1847. _Flora Novæ Zelandiæ_. 1853.]

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 science--a 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. {632}

Dr. Hooker's remarks on the limits of species, their dispersion and variation, are striking and instructive. He is of opinion that species vary more, and are more widely diffused, than is usually supposed. Hence he conceives that the number of species has been needlessly and erroneously multiplied, by distinguishing the specimens which occur in different places, and vary in unessential features. He says that though, according to the lowest estimate of compilers, 100,000 is the commonly received number of known plants, he thinks that half that number is much nearer the truth. "This," he says, "may be well conceived, when it is notorious that nineteen species have been made of the Common Potatoe, and many more of _Solanum nigrum_ alone. _Pteris aquilina_ has given rise to numerous book species; _Vernonia cinerea_ of India to fifteen at least. . . . . . . Many more plants are common to most countries than is supposed; I have found 60 New Zealand flowering plants and 9 Ferns to be European ones, besides inhabiting numerous intermediate countries. . . . . . So long ago as 1814, Mr. Brown drew attention to the importance of such considerations, and gave a list of 150 European plants common to Australia."

As an example of the extent to which unessential differences may go, he says (p. xvii.,) "The few remaining native Cedars of Lebanon may be abnormal states of the tree which was once spread over the whole of the Lebanon; for there are now growing in England varieties of it which have no existence in a wild state. Some of them closely resemble the Cedars of Atlas and of the Himalayas (_Deodar_;) and the absence of any valid botanical differences tends to prove that all, though generally supposed to be different species, are one."

Still the great majority of the species of plants in those Southern regions are peculiar. "There are upwards of 100 genera, subgenera, or other well marked groups of plants, entirely or nearly confined to New Zealand, Australia, and extra-tropical South America. They are represented by one or more species in two or more of those countries, and thus effect a botanical relationship or affinity between them all which every botanist appreciates."

In reference to the History of Botany, I have received corrections and remarks from Dr. Hooker, with which I am allowed to enrich my pages.

"P. 359. Note ^3. ~= Note 3\16~ _Nelumbium speciosum_, the Lotus of India. The _Nelumbium_ does not float, but raises both leaf and flower several feet above the water: the _Nymphæa Lotus_ has floating leaves. Both enter largely into the symbolism of the Hindoos, and are often confounded. {633}

"P. 362. Note ^5. ~= Note 13\16~ For _Arachnis_ read _Arachis_. The _Arachidna_ of Theophrastus cannot, however, be the _Arachis_ or ground-nut.

"Pp. 388 and 394. For _Harlecamp_ read _Hartecamp_.

"P. 394. For _Kerlen_ read _Kalm_.

"P. 394. For _Asbech_ read _Osbeck_.

"P. 386. _John Ray_. Ray was further the author of the present Natural System in its most comprehensive sense. He first divided plants into Flowerless and Flowering; and the latter into Monocotyledonous and Dicotyledonous:--'Floriferas dividemus in DICOTYLEDONES, quarum semina sata binis foliis, seminalibus dictis, quæ cotyledonorum usum præstant, e terra exeunt, vel in binos saltem lobos dividuntur, quamvis eos supra terram foliorum specie non efferant; et MONOCOTYLEDONES, quæ nec folia bina seminalia efferunt nec lobos binos condunt. Hæc divisio ad arbores etiam extendi potest; siquidem Palmæ et congeneres hoc respectu eodem modo a reliquis arboribus differunt quo Monocotyledones a reliquis herbis.'

"P. 408. _Endogenous and Exogenous Growth._ The exact course of the wood fibres which traverse the stems of both Monocotyledonous and Dicotyledonous plants has been only lately discovered. In the Monocotyledons, those fibres are collected in bundles, which follow a very peculiar course:--from the base of each leaf they may be followed downwards and inwards, towards the axis of the trunk, when they form an arch with the convexity to the centre; and curving outwards again reach the circumference, where they are lost amongst the previously deposited fibres. The intrusion of the bases of these bundles amongst those already deposited, causes the circumference of the stem to be harder than the centre; and as all these arcs have a short course (their chords being nearly equal), the trunk does not increase in girth, and grows at the apex only. The wood-bundles are here definite. In the Dicotyledonous trunks, the layers of wood run in parallel courses from the base to the top of the trunk, each externally to that last formed, and the trunk increases both in height and girth; the wood-bundles are here indefinite.

"With regard to the Cotyledons, though it is often difficult to distinguish a Monocotyledonous Embryo from a Dicotyledonous, they may always be discriminated when germinating. The Cotyledons, when two or more, and primordial leaves (when no Cotyledons are visible) of a Monocotyledon, are alternate; those of a Dicotyledon are opposite.

"A further physiological distinction between Monocotyledons and {634} Dicotyledons is observed in germination, when the Dicotyledonous radicle elongates and forms the root of the young plant; the Monocotyledonous radicle does not elongate, but pushes out rootlets from itself at once. Hence the not very good terms, _exorhizal_ for Dicotyledonous, and _endorhizal_ for Monocotyledonous.

"The highest physiological generalization in the vegetable kingdom is between _Phænogama_ and _Cryptogama_. In the former, fertilization is effected by a pollen-tube touching the nucleus of an ovule; in Cryptogams, the same process is effected by the contact of a sperm-cell, usually ciliated (_antherozoid_), upon another kind of cell called a germ-cell. In Phænogams, further, the organs of fructification are all modified leaves; those of Cryptogams are not homologous." (J. D. H.)

ZOOLOGY.

I have exemplified the considerations which govern zoological classification by quoting the reflexions which Cuvier gives us, as having led him to his own classification of Fishes. Since the varieties of Quadrupeds, or _Mammals_ (omitting whales, &c.), are more familiar to the common reader than those of Fishes, I may notice some of the steps in their classification; the more so as some curious questions have recently arisen thereupon.

Linnæus first divides Mammals into two groups, as they have Claws, or Hoofs (_unguiculata_, _ungulata_.) But he then again divides them into six orders (omitting whales, &c.), according to their number of _incisor_, _laniary_, and _molar_ teeth; namely:-- _Primates_. (Man, Monkey, &c.) _Bruta_. (Rhinoceros, Elephant, &c.) _Feræ_. (Dog, Cat, Bear, Mole, &c.) _Glires_. (Mouse, Squirrel, Hare, &c.) _Pecora_. (Camel, Giraffe, Stag, Goat, Sheep, Ox, &c.) _Belluæ_. (Horse, Hippopotamus, Tapir, Sow, &c.)

In the place of these, Cuvier, as I have stated in the _Philosophy_ (_On the Language of Sciences_, Aphorism xvi.), introduced the following orders: _Bimanes_, _Quadrumanes_, _Carnassiers_, _Rongeurs_, _Edentés_, _Pachyderms_, _Ruminans_. Of these, the _Carnassiers_ correspond to the _Feræ_ of Linnæus; the _Rongeurs_ to his _Glires_; the _Edentés_ are a new order, taking the Sloths, Ant-eaters, &c., from the _Bruta_ of Linnæus, the Megatherium from extinct animals, and the Ornithorhynchus, &c., from the new animals of Australia; the _Ruminans_ agree with the {635} _Pecora_; the _Pachyderms_ include some of the _Bruta_ and the _Belluæ_, comprehending also extinct animals, as _Anoplotherium_ and _Palæotherium_.

But the two orders of Hoofed Animals, the Pachyderms and the Ruminants, form a group which is held by Mr. Owen to admit of a better separation, on the ground of a character already pointed out by Cuvier; namely, as to whether they are _two-toed_ or _three-toed_. According to this view, the Horse is connected with the Tapir, the Palæotherium, and the Rhinoceros, not only by his teeth, but by his feet, for he has really three digits. And Cuvier notices that in the two-toed or even-toed Pachyderms, the astragalus bone has its face divided into two equal parts by a ridge; while in the uneven-toed pachyderms it has a narrow cuboid face. Mr. Owen has adopted this division of Pachyderms and Ruminants, giving the names _artiodactyla_ and _perissodactyla_ to the two groups; the former including the Ox, Hog, Peccary, Hippopotamus, &c.; the latter comprehending the Horse, Tapir, Rhinoceros, Hyrax, &c. And thus the Ruminants take their place as a subordinate group of the great natural even-toed Division of the Hoofed Section of Mammals; and the Horse is widely separated from them, inasmuch as he belongs to the odd-toed division.[42\B]

[Note 42\B: Owen, _Odontography_.]

As we have seen, these modern classifications are so constructed as to include extinct as well as living species of animals; and indeed the species which have been discovered in a fossil state have tended to fill up the gaps in the series of zoological forms which had marred the systems of modern zoologists. This has been the case with the division of which we are speaking.

Mr. Owen had established two genera of extinct Herbivorous Animals, on the strength of fossil remains brought from South America:--_Toxodon_, and _Nesodon_. In a recent communication to the Royal Society[43\B] he has considered the bearing of these genera upon the divisions of odd-toed and even-toed animals. He had already been led to the opinion that the three sections, _Proboscidea_, _Perissodactyla_, and _Artiodactyla_, formed a natural division of Ungulata; and he is now led to think that this division implies another group, "a distinct division of the _Ungulata_, of equal value, if not with the _Perissodactyla_ and _Artiodactyla_ at least with the _Proboscidea_. This group he proposes to call _Toxodonta_.

[Note 43\B: _Phil. Trans._, 1853.]

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## BOOK XVII.

PHYSIOLOGY AND COMPARATIVE ANATOMY.

VEGETABLE MORPHOLOGY.

_Morphology in Linnæus._

I HAVE stated that Linnæus had some views on this subject. Dr. Hooker conceives these views to be more complete and correct than is generally allowed, though unhappily clothed in metaphorical language and mixed with speculative matter. By his permission I insert some remarks which I have received from him.

The fundamental passage on this subject is in the _Systema Naturæ_; in the Introduction to which work the following passage occurs:--

"Prolepsis (Anticipation) exhibits the mystery of the metamorphosis of plants, by which the herb, which is the _larva_ or imperfect condition, is changed into the declared fructification: for the plant is capable of producing either a leafy herb or a fructification. . . . . .

"When a tree produces a flower, nature anticipates the produce of five years where these come out all at once; forming of the bud-leaves of the next year _bracts_; of those of the following year, the _calyx_; of the following, the _corolla_; of the next, the _stamina_; of the subsequent, the _pistils_, filled with the granulated marrow of the seed, the terminus of the life of a vegetable."

Dr. Hooker says, "I derive my idea of his having a better knowledge of the subject than most Botanists admit, not only from the Prolepsis, but from his paper called _Reformatio Botanices_ (_Amœn. Acad._ vol. vi.); a remarkable work, in respect of his candor in speaking of his predecessors' labors, and the sagacity he shows in indicating researches to be undertaken or completed. Amongst the latter is V. 'Prolepsis plantarum, ulterius extendenda per earum metamorphoses.' The last word occurs rarely in his _Prolepsis_; but when it does it seems to me that he uses it as indicating a normal change and not an accidental one. {637}

"In the _Prolepsis_ the speculative matter, which Linnæus himself carefully distinguishes as such, must be separated from the rest, and this may I think be done in most of the sections. He starts with explaining clearly and well the origin and position of buds, and their constant presence, whether developed or not, in the axil of the leaf: adding abundance of acute observations and experiments to prove his statements. The leaf he declares to be the first effort of the plant in spring: he proceeds to show, successively, that bracts, calyx, corolla, stamens, and pistil are each of them metamorphosed leaves, in every case giving MANY EXAMPLES, both from monsters and from characters presented by those organs in their normal condition.

"The (to me) obscure and critical part of the _Prolepsis_ was that relating to the change of the style of _Carduus_ into two leaves. Mr. Brown has explained this. He says it was a puzzle to him, till he went to Upsala and consulted Fries and Wahlenberg, who informed him that such monstrous _Cardui_ grew in the neighborhood, and procured him some. Considering how minute and masked the organs of _Compositæ_ are, it shows no little skill in Linnæus, and a very clear view of the whole matter, to have traced the metamorphosis of all their floral organs into leaves, except their stamens, of which he says, 'Sexti anni folia e staminibus me non in compositis vidisse fateor, sed illorum loco folia pistillacea, quæ in compositis aut plenis sunt frequentissima.' I must say that nothing could well be clearer to my mind than the full and accurate appreciation which Linnæus shows of the whole series of phenomena, and their _rationale_. He over and over again asserts that these organs are leaves, every one of them,--I do not understand him to say that the prolepsis is an accidental change of leaves into bracts, of bracts into calyx, and so forth. Even were the language more obscure, much might be inferred from the wide range and accuracy of the observations he details so scientifically. It is inconceivable that a man should have traced the sequence of the phenomena under so many varied aspects, and shown such skill, knowledge, ingenuity, and accuracy in his methods of observing and describing, and yet missed the _rationale_ of the whole. Eliminate the speculative parts and there is not a single error of observation or judgment; whilst his history of the developement of buds, leaves, and floral organs, and of various other obscure matters of equal interest and importance, are of a very high order of merit, are, in fact, for the time profound.

"There is nothing in all this that detracts from the merit of Goethe's {638} re-discovery. With Goethe it was, I think, a deductive process,--with Linnæus an inductive. Analyse Linnæus's observations and method, and I think it will prove a good example of inductive reasoning.

"P. 473. Perhaps Professor Auguste St Hilaire of Montpellier should share with De Candolle the honor of contributing largely to establish the metamorphic doctrine;--their labors were cotemporaneous.

"P. **474. Linnæus pointed out that the pappus was calyx: 'Et _pappum_ gigni ex quarti anni foliis, in jam nominatis Carduis.'--_Prol. Plant._ 338." (_J. D. H._)

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