M. Wertheim also employed the vibrations_History of the inductive sciences, from the earliest to the present time

metals in order to determine their _modulus of elasticity_--that is,

the quantity which determines for each substance, the extent to

which, in virtue of its elasticity, it is compressed and expanded by

given pressures or tensions. For this purpose he caused the rod to

vibrate near to a tuning-fork of given pitch, so that both the rod

and the tuning-fork by their vibrations traced undulating curves on

a revolving disk. The curves traced by the two could be compared so

as to give their relative rate, and thus to determine the elasticity

of the substance.

BOOK IX.

PHYSICAL OPTICS.

_Photography._

I HAVE, at the end of Chapter xi., stated that the theory of which I

have endeavored to sketch the history professes to explain only the

phenomena of radiant visible light; and that though we know that

light has other properties--for instance, that it produces chemical

effects--these are not contemplated as included within the domain of

the theory. The chemical effects of light cannot as yet be included

in exact and general truths, such as those which constitute the

undulatory theory of radiant visible light. But though the present

age has not yet attained to a _Science_ of the chemistry of Light,

it has been enriched with a most exquisite _Art_, which involves the

principles of such a science, and may hereafter be made the

instrument of bringing them into the view of the philosopher. I

speak of the Art of _Photography_, in which chemistry has discovered

the means of producing surfaces almost as sensitive to the

modifications of light as the most sensitive of organic textures,

the retina of the eye: and has given permanence to images which in

the eye are only momentary impressions. Hereafter, when the laws

shall have been theoretically established, which connect the

chemical constitution of bodies with the action of light upon them,

the prominent names in the Prelude to such an Epoch must be those

who by their insight, invention, and perseverance, discovered and

carried to their present marvellous perfection the processes of

photographic Art:--Niepce and Daguerre in France, and our own

accomplished countryman, Mr. Fox Talbot.

_Fluorescence._

As already remarked, it is not within the province of the undulatory

theory to explain the phenomena of the absorption of light which

take place in various ways when the light is transmitted through

various {602} mediums. I have, at the end of Chapter iii., given the

reasons which prevent my assenting to the assertion of a special

analysis of light by absorption. In the same manner, with regard to

other effects produced by media upon light, it is sufficient for the

defence of the theory that it should be consistent with the

possibility of the laws of phenomena which are observed, not that it

should explain those laws; for they belong, apparently, to another

province of philosophy.

Some of the optical properties of bodies which have recently

attracted notice appear to be of this kind. It was noticed by Sir

John Herschel,[4\B] that a certain liquid, sulphate of quinine,

which is under common circumstances colorless, exhibits in certain

aspects and under certain incidences of light, a beautiful celestial

blue color. It appeared that this color proceeded from the surface

on which the light first fell; and color thus produced Sir J.

Herschel called _epipolic_ colors, and spoke of the light as

_epipolized_. Sir David Brewster had previously noted effects of

color in transparent bodies which he ascribed to internal

dispersion:[5\B] and he conceived that the colors observed by Sir J.

Herschel were of the same class. Professor Stokes[6\B] of Cambridge

applied himself to the examination of these phenomena, and was led

to the conviction that they arise from a power which certain bodies

possess, of changing the color, and with it, the refrangibility of

the rays of light which fall upon them: and he traced this property

in various substances, into various remarkable consequences. As this

change of refrangibility always makes the rays _less_ refrangible,

it was proposed to call it a _degradation_ of the light; or again,

_dependent emission_, because the light is emitted in the manner of

self-luminous bodies, but only in dependence upon the active rays,

and so long as the body is under their influence. In this respect it

differs from _phosphorescence_, in which light is emitted without

such dependence. The phenomenon occurs in a conspicuous and

beautiful manner in certain kinds of fluor spar: and the term

_fluorescence_, suggested by Professor Stokes, has the advantage of

inserting no hypothesis, and will probably be found the most

generally acceptable.[7\B]

[Note 4\B: _Phil. Trans._ 1845.]

[Note 5\B: _Edinb. Trans._ 1833.]

[Note 6\B: _Phil. Trans._ 1852 and 1854.]

[Note 7\B: _Phil. Trans._ 1852.]

It may be remarked that Professor Stokes rejects altogether the

doctrine that light of definite refrangibility may still be

compound, and maybe analysed by absorption. He says, "I have not

overlooked the remarkable effect of absorbing media in causing

apparent changes {603} of color in a pure spectrum; but this I

believe to be a subjective phenomenon depending upon contrast."

CHAPTER XIII.

UNDULATORY THEORY.

_Direction of the Transverse Vibrations in Polarization._

IN the conclusion of Chapter xiii. I have stated that there is a

point in the undulatory theory which was regarded as left undecided

by Young and Fresnel, and on which the two different opinions have

been maintained by different mathematicians; namely, whether the

vibrations of polarized light are perpendicular to the plane of

polarization or in that plane. Professor Stokes of Cambridge has

attempted to solve this question in a manner which is,

theoretically, exceedingly ingenious, though it is difficult to make

the requisite experiments in a decisive manner. The method may be

briefly described.

If polarized light be _diffracted_ (see Chap. xi. sect. 2), each ray

will be bent from its position, but will still be polarized. The

original ray and the diffracted ray, thus forming a broken line, may

be supposed to be connected at the angle by a universal joint

(called a _Hooke's Joint_), such that when the original ray turns

about its axis, the diffracted ray also turns about its axis; as in

the case of the long handle of a telescope and the screw which is

turned by it. Now if the motion of the original ray round its axis

be uniform, the motion of the diffracted ray round its axis is not

uniform: and hence if, in a series of cases, the planes of

polarization of the original ray differ by equal angles, in the

diffracted ray the planes of polarization will differ by unequal

angles. Then if vibrations be perpendicular to the plane of

polarization, the planes of polarization in the diffracted rays will

be crowded together in the neighborhood of the plane in which the

diffraction takes place, and will be more rarely distributed in the

neighborhood of the plane perpendicular to this, in which is the

diffracting thread or groove.

On making the experiment, Prof. Stokes conceived that he found, in

his experiments, such a crowding of the planes of diffracted

polarization towards the plane of diffraction; and thus he held that

the {604} hypothesis that the transverse vibrations which constitute

polarization are perpendicularly transverse to the plane of

polarization was confirmed.[8\B]

[Note 8\B: _Camb. Trans._, vol. ix. part i. 1849.]

But Mr. Holtzmann,[9\B] who, assenting to the reasoning, has made

the experiment in a somewhat different manner, has obtained an

opposite result; so that the point may be regarded as still

doubtful.

[Note 9\B: _Phil. Mag._, Feb. 1857.]

_Final Disproof of the Emission Theory._

As I have stated in the History, we cannot properly say that there

ever was an Emission Theory of Light which was the _rival_ of the

Undulatory Theory: for while the undulatory theory provided

explanations of new classes of phenomena as fast as they arose, and

exhibited a _consilience_ of theories in these explanations, the

hypothesis of emitted particles required new machinery for every new

set of facts, and soon ceased to be capable even of expressing the

facts. The simple cases of the ordinary reflexion and refraction of

light were explained by Newton on the supposition that the

transmission of light is the motion of particles: and though his

explanation includes a somewhat harsh assumption (that a refracting

surface exercises an attractive force through a _fixed finite_

space), the authority of his great name gave it a sort of permanent

notoriety, and made it to be regarded as a standard point of

comparison between a supposed "Emission Theory" and the undulation

theory. And the way in which the theories were to be tested in this

case was obvious: in the Newtonian theory, the velocity of light is

increased by the refracting medium; in the undulatory theory, it is

diminished. On the former hypothesis the velocity of light in air

and in water is as 3 to 4; in the latter, as 4 to 3.

But the immense velocity of light made it appear impossible to

measure it, within the limits of any finite space which we can

occupy with refracting matter. The velocity of light is known from

astronomical phenomena;--from the eclipses of Jupiter's satellites,

by which it appears that light occupies 8 minutes in coming from the

sun to the earth; and from the aberration of light, by which its

velocity is shown to be 10,000 times the velocity of the earth in

its orbit. Is it, then, possible to make apparent so small a

difference as that between its passing through a few yards of air

and of water?

Mr. Wheatstone, in 1831, invented a machine by which this could

{605} be done. His object was to determine the velocity of the

electric shock. His apparatus consisted in a small mirror, turning

with great velocity about an axis which is in its own plane, like a

coin spinning on its edge. The velocity of spinning may be made so

great, that an object reflected shall change its place perceptibly

after an almost inconceivably small fraction of a second. The

application of this contrivance to measure the velocity of light,

was, at the suggestion of Arago, who had seen the times of the rival

theories of light, undertaken by younger men at Paris, his eyesight

not allowing him to prosecute such a task himself. It was necessary

that the mirrors should turn more than 1000 times in a second, in

order that the two images, produced, one by light coming through

air, and the other by light coming through an equal length of water,

should have places perceptibly different. The mechanical

difficulties of the experiment consisted in keeping up this great

velocity by the machinery without destroying the machinery, and in

transmitting the light without too much enfeebling it. These

difficulties were overcome in 1850, by M. Fizeau and M. Léon

Foucault separately: and the result was, that the velocity of light

was found to be less in water than in air. And thus the Newtonian

explanation of refraction, the last remnant of the Emission Theory,

was proved to be false.

BOOK X.

THERMOTICS.--ATMOLOGY.

CHAPTER III.

THE RELATION OF VAPOUR AND AIR.

_Sect._ 4.--_Force of Steam._

THE experiments on the elastic force of steam made by the French

Academy are fitted in an especial manner to decide the question

between rival formulæ, in consequence of the great amount of force

to which they extend; namely, 60 feet of mercury, or 24 atmospheres:

for formulæ which give results almost indistinguishable in the lower

part of the scale diverge widely at those elevated points. Mr.

Waterston[10\B] has reduced both these and other experiments to a

rule in the following manner:--He takes the zero of gaseous tension,

determined by other experimenters (Rudberg, Magnus, and Regnault,)

to be 461° below the zero of Fahrenheit, or 274° below the zero of

the centigrade scale: and temperatures reckoned from this zero he

calls "G temperatures." The square root of the G temperatures is the

element to which the elastic force is referred (for certain

theoretical reasons), and it is found that the density of steam is

as the _sixth power_ of this element. The agreement of this rule

with the special results is strikingly close. A like rule was found

by him to apply generally to many other gases in contact with their

liquids.

[Note 10\B: _Phil. Trans._ 1852.]

But M. Regnault has recently investigated the subject in the most

complete and ample manner, and has obtained results somewhat

different.[11\B] He is led to the conclusion that no formula

proceeding by {607} a power of the temperature can represent the

experiments. He also finds that the rule of Dalton (that as the

temperatures increase in arithmetical progression, the elastic force

increases in geometric progression) deviates from the observations,

especially at high temperatures. Dalton's rule would be expressed by

saying that the variable part of the elastic force is as _a^t_, where

_t_ is the temperature. This failing, M. Regnault makes trial of a

formula suggested by M. Biot, consisting of a sum of two terms, one of

which is as _a^t_, and the other is _b^t_: and in this way satisfies

the experiments very closely. But this can only be considered as a

formula of interpolation, and has no theoretical basis. M. Roche had

proposed a formula in which the force is as _a^z_, _z_ depending upon

the temperature by an equation[12\B] to which he had been led by

theoretical considerations. This agrees better with observation than

any other formula which includes only the same number of coefficients.

[Note 11\B: _Mém. de l'Institut_, vol. xxi. (1847). M. Regnault's

Memoir occupies 767 pages.]

[Note 12\B: The equation _z_ = _t_ ⁄ (1 + _mt_).]

Among the experimental thermotical laws referred to by M. Regnault

are, the Law of Watt,[13\B] that "the quantity of heat which is

required to convert a pint of water at a temperature of zero into

steam, is the same whatever be the pressure." Also, the Law of

Southern, that "the latent heat of vaporization, that is the heat

absorbed in the passage from the liquid to the gaseous consistence,

is constant for all purposes: and that we obtain the total heat in

adding to the constant latent heat the number which represents the

latent heat of steam." Southern found the latent heat of the steam

of water to be represented by about 950 degrees of Fahrenheit.[14\B]

[Note 13\B: See Robison's _Mechanical Philosophy_, vol. ii. p. 8.]

[Note 14\B: Ib. p. 160.]

_Sect._ 5.--_Temperature of the Atmosphere._

I MAY notice, as important additions to our knowledge on this

subject, the results of four balloon ascents made in 1852,[15\B] by

the Committee of the Meteorological Observatory established at Kew

by the British Association for the Advancement of Science. In these

ascents the observers mounted to more than 13,000, 18,000, and

19,000 feet, and in the last to 22,370; by which ascent the

temperature fell from 49 degrees to nearly 10 degrees below zero;

and the dew-point fell from 37° to 12°. Perhaps the most marked

result of these observations is the {608} following:--The temperature

of the air decreases uniformly as we ascend above the earth's

surface; but this decrease does not go on continuously. At a certain

elevation, varying on different days, the decrease is arrested: and

for a depth of two or three thousand feet of air, the temperature

decreases little, or even increases in ascending. Above this, the

diminution again takes place at nearly the same rate as in the lower

regions. This intermediate region of undecreasing temperature

extended in the various ascents, from about altitude 4000 to 6000

feet, 6500 to 10,000, 2000 to 4500, and 4000 to 8000. This

interruption in the decrease of temperature is accompanied by a

large and abrupt fall in the temperature of the dew-point, or by an

actual condensation of vapor. Thus, this region is the _region of

the clouds_, and the increase of heat appears to arise from the

latent heat liberated when aqueous vapor is formed into clouds.

[Note 15\B: _Phil. Trans._ 1853.]

CHAPTER IV.

THEORIES OF HEAT.

_The Dynamical Theory of Heat._

THAT the transmission of _radiant_ Heat takes place by means of the

vibrations of a medium, as the transmission of Sound certainly does,

and the transmission of Light most probably, is a theory which, as I

have endeavored to explain, has strong arguments and analogies in

its favor. But that Heat itself, in its essence and quantity, is

Motion is a hypothesis of quite another kind. This hypothesis has

been recently asserted and maintained with great ability. The

doctrine thus asserted is, that Motion may be converted into Heat,

and Heat into Motion; that Heat and Motion may produce each other,

as we see in the rarefaction and condensation of air, in

steam-engines, and the like: and that in all such cases the Motion

produced and the Heat expended exactly measure each other. The

foundation of this theory is conceived to have been laid by Mr.

Joule of Manchester, in 1844: and it has since been prosecuted by

him and by Professor Thomson of Glasgow, by experimental

investigations of various kinds. It is difficult to make these

experiments so as to be quite satisfactory; for it is {609}

difficult to measure _all_ the heat gained or lost in any of the

changes here contemplated. That friction, agitation of fluids,

condensation of gases, conversion of gases into fluids and liquids

into solids, produce heat, is undoubted: and that the quantity of

such heat may be measured by the mechanical force which produces it,

or which it produces, is a generalization which will very likely be

found a fertile source of new propositions, and probably of

important consequences.

As an example of the conclusions which Professor Thomson draws from

this doctrine of the mutual conversion of motion and heat, I may

mention his speculations concerning the cause which produces and

sustains the heat of the sun.[16\B] He conceives that the support of

the solar heat must be meteoric matter which is perpetually falling

towards the globe of the sun, and has its motion converted into

heat. He inclines to think that the meteors containing the stores of

energy for future Sun-light must be principally within the earth's

orbit; and that we actually see them there as the "Zodiacal Light,"

an illuminated shower, or rather tornado, of stones. The inner parts

of this tornado are always getting caught in the Sun's atmosphere,

and drawn to his mass by gravitation.

[Note 16\B: On the Mechanical Energies of the Solar System. _Edinb.

Trans._ vol. XXI. part i. (1854), p. 67.]

BOOK XI.

ELECTRICITY.

GENERAL REMARKS.

ELECTRICITY in the form in which it was originally

studied--Franklinic, frictional, or statical electricity--has been

so completely identified with electricity in its more comprehensive

form--Voltaic, chemical, or dynamical electricity--that any

additions we might have to make to the history of the earlier form

of the subject are included in the later science.

There are, however, several subjects which may still be regarded

rather as branches of Electricity than of the Cognate Sciences. Such

are, for instance, Atmospheric Electricity, with all that belongs to

Thunderstorms and Lightning Conductors. The observation of

Atmospheric Electricity has been prosecuted with great zeal at

various meteorological observatories; and especially at the

Observatory established by the British Association at Kew. The

Aurora Borealis, again, is plainly an electrical phenomenon; but

probably belonging rather to dynamical than to statical electricity.

For it strongly affects the magnetic needle, and its position has

reference to the direction of magnetism; but it has not been

observed to affect the electroscope. The general features of this

phenomenon have been described by M. de Humboldt, and more recently

by M. de Bravais; and theories of the mode of its production have

been propounded by MM. Biot, De la Rive, Kaemtz, and others.

Again, there are several fishes which have the power of giving an

electrical shock:--the torpedo, the gymnotus, and the silurus. The

agency of these creatures has been identified with electricity in

the most general sense. The peculiar energy of the animal has been

made to produce the effects which are produced by an electrical

discharge or a voltaic current:--not only to destroy life in small

animals, but to {611} deflect a magnet, to make a magnet, to

decompose water, and to produce a spark.

_Dr. Faraday's Views of Statical Electric Induction._

According to the theories of electricity of Æpinus and Coulomb,

which in this Book of our History are regarded as constituting a

main part of the progress of this portion of science, the particles

of the electric fluid or fluids exert forces, attractive and

repulsive, upon each other in straight lines at a distance, in the

same way in which, in the Newtonian theory of the universe, the

particles of matter are conceived as exerting attractive forces upon

each other. An electrized body presented a conducting body of any

form, determines a new arrangement of the electric fluids in the

conductor, attracting the like fluid to its own side, and repelling

the opposite fluid to the opposite side. This is Electrical

_Induction_. And as, by the theory, the attraction is greater at the

smaller distances, the distribution of the fluid upon the conductor

in virtue of this Induction will not be symmetrical, but will be

governed by laws which it will require a complex and difficult

calculation to determine--as we have seen was the case in the

investigations of Coulomb, Poisson, and others.

Instead of this action at a distance. Dr. Faraday has been led to

conceive Electrical Induction to be the result of an action taking

place between the electrized body and the conductor through lines of

contiguous particles in the mass of the intermediate body, which he

calls the _Dielectric_. And the irregularities of the distribution

of the electricity in these cases of Induction, and indeed the

existence of an action in points protected from direct action by the

protuberant sides of the conductor, are the causes, I conceive,

which lead him to the conclusion that Induction takes place in

_curved lines_[17\B] of such contiguous particles.

[Note 17\B: _Researches_, 1165, &c.]

With reference to this, I may remark that, as I have said, the

distribution of electricity on a conductor in the presence of an

electrized body is so complex a mathematical problem that I do not

conceive any merely popular way of regarding the result can entitle

us to say, that the distribution which we find cannot be explained

by the Coulombian theory, and must force us upon the assumption of

an action in curved lines:--which is, indeed, itself a theory, and

so vague a one {612} that it requires to be made much more precise

before we can say what consequences it does or does not lead to.

Professor W. Thomson has arrived at a mathematical proof that the

effect of induction on the view of Coulomb and of Faraday must,

under certain conditions, be necessarily and universally the same.

With regard to the influence of different _Dielectrics_ upon

Induction, the inquiry appears to be of the highest importance; and

may certainly necessitate some addition to the theory.

BOOK XII.

MAGNETISM.

_Recent Progress of Terrestrial Magnetism._

IN Chapter II., I have noticed the history of Terrestrial Magnetism;

Hansteen's map published in 1819; the discovery of "magnetic storms"

about 1825; the chain of associated magnetic observations, suggested

by M. de Humboldt, and promoted by the British Association and the

Royal Society; the demand for the continuation of these till 1848;

the magnetic observations made in several voyages; the magnetic

surveys of various countries. And I have spoken also of Gauss's

theory of Terrestrial Magnetism, and his directions and requirements

concerning the observations to be made. I may add a few words with

regard to the more recent progress of the subject.

The magnetic observations made over large portions of the Earth's

surface by various persons, and on the Ocean by British officers,

have been transmitted to Woolwich, where they have been employed by

General Sabine in constructing magnetic maps of the Earth for the

year 1840.[18\B] Following the course of inquiry described in the

part of the history referred to, these maps exhibit the declination,

inclination, and intensity of the magnetic force at every point of

the earth's surface. The curves which mark equal amounts of each of

these three elements (the _lines of equal declination_,

_inclination_, and _force_:--the _isogonal_, the _isoclinal_, and

the _isodynamic_ lines,) are, in their general form, complex and

irregular; and it has been made a matter of question (the facts

being agreed upon) whether it be more proper to say that they

indicate four poles, as Halley and as Hansteen said, or only two

poles, as Gauss asserts. The matter appears to become more clear if

we draw magnetic _meridians_; that is, lines obtained by following

the directions, or pointings, of the magnetic needle to the north or

to {614} the south, till we arrive at the points of convergence of

all their directions; for there are only two such poles, one in the

Arctic and one in the Antarctic region. But in consequence of the

irregularity of the magnetic constitution of the earth, if we follow

the inclination of the magnetic force round the earth on any

parallel of latitude, we find that it has two _maxima_ and two

_minima_, as if there were four magnetic poles. The isodynamic map

is a new presentation of the facts of this subject; the first having

been constructed by Colonel Sabine in 1837.

[Note 18\B: These maps are published in Mr. Keith Johnstone's

_Physical Atlas_.]

I have stated also that the magnetic elements at each place are to

be observed in such a manner as to bring into view both their

_periodical_, their _secular_, and their _irregular_ or _occasional_

changes. The observations made at Toronto in Canada, and at Hobart

Town in Van Diemen's Land, two stations at equal distances from the

two poles of the earth, and also at St Helena, a station within the

tropics, have been discussed by General Sabine with great care, and

with an amount of labor approaching to that employed upon reductions

of astronomical observations. And the results have been curious and

unexpected.

The declination was first examined.[19\B] This magnetical element is,

as we have already seen (p. 232), liable both to a diurnal and to an

annual inequality; and also to irregular perturbations which have been

termed magnetic storms. Now it was found that all these inequalities

went on increasing gradually and steadily from 1843 to 1848, so as to

become, at the end of that time, above twice as large as they were at

the beginning of it. A new periodical change in all these elements

appeared to be clearly established by this examination. M. Lamont, of

Munich, had already remarked indications of a decennial period in the

diurnal variation of the declination of the needle. The duration of

the period from minimum to maximum being about five years, and

therefore the whole period about ten years. The same conclusion was

found to follow still more decidedly from the observations of the dip

and intensity.

[Note 19\B: _Phil. Trans._ 1852 and 1856.]

This period of ten years had no familiar meaning in astronomy; and

if none such had been found for it, its occurrence as a magnetic

period must have been regarded, as General Sabine says,[20\B] in the

light of a fragmentary fact. But it happened about this time that

the scientific world was made aware of the existence of a like

period in a {615} phenomenon which no one would have guessed to be

connected with terrestrial magnetism, namely, the spots in the Sun.

M. Schwabe, of Dessau, had observed the Sun's disk with immense

perseverance for 24 years:--often examining it more than 300 days in

the year; and had found that the spots had, as to their quantity and

frequency, a periodical character. The years of maximum are 1828,

1838, 1848, in which there were respectively 225,[21\B] 282, 330

groups of spots. The minimum years, 1833, 1843, had only 33 and 34

such groups. This curious fact[22\B] was first made public by M. de

Humboldt, in the third volume of his _Kosmos_ (1850). The

coincidence of the periods and epochs of these two classes of facts

was pointed out by General Sabine in a Memoir presented to the Royal

Society in March, 1852.

[Note 20\B: _Phil. Trans._ 1856, p. 382.]

[Note 21\B: In 1837 there were 333.]

[Note 22\B: The observations up to 1844 were published in

Poggendorf's _Annalen_.]

Of course it was natural to suppose, even before this discovery,

that the diurnal and annual inequalities of the magnetic element at

each place depend upon the action of the sun, in some way or other.

Dr. Faraday had endeavored to point out how the effect of the solar

heat upon the atmosphere would, according to the known relations of

heat and magnetism, explain many of the phenomena. But this new

feature of the phenomena, their quinquennial increase and decrease,

makes us doubt whether such an explanation can really be the true one.

Of the _secular_ changes in the magnetic elements, not much more is

known than was known some years ago. These changes go on, but their

laws are imperfectly known, and their causes not even conjectured.

M. Hansteen, in a recent memoir,[23\B] says that the decrease of the

inclination goes on progressively diminishing. With us this rate of

decrease appears to be at present nearly uniform. We cannot help

conjecturing that the sun, which has so plain a connexion with the

diurnal, annual, and occasional movements of the needle, must also

have some connexion with its secular movements.

[Note 23\B: See K. Johnstone's _Physical Atlas_.]

In 1840 the observations made at various places had to a great

extent enabled Gauss, in connexion with W. Weber, to apply his

Theory to the actual condition of the Earth;[24\B] and he

calculated the Declination, Inclination, and Intensity at above 100

places, and found {616} the agreement, as he says, far beyond his

hopes. They show, he says, that the Theory comes near to the Truth.

[Note 24\B: _Atlas des Erdmagnetismus nach den Elementen der Theorie

Entworfen_. See Preface.]

_Correction of Ship's Compasses._

The magnetic needle had become of importance when it was found that

it always pointed to the North. Since that time the history of

magnetism has had its events reflected in the history of navigation.

The change of the declination arising from a change of place

terrified the companions of Columbus. The determination of the laws

of this change was the object of the voyage of Halley; and has been

pursued with the utmost energy in the Arctic and Antarctic regions

by navigators up to the present time. Probably the dependence of the

magnetic declination upon place is now known well enough for the

purposes of navigation. But a new source of difficulty has in the

meantime come into view; the effect of the iron in the ship upon the

Compass. And this has gone on increasing as guns, cables, stays,

knees, have been made of iron; then steam-engines with funnels,

wheels, and screws, have been added; and finally the whole ship has

been made of iron. How can the compass be trusted in such cases?

I have already said in the history that Mr. Barlow proposed to

correct the error of the compass by placing near to the compass an

iron plate, which from its proximity to the compass might

counterbalance magnetically the whole effect of the ship's iron upon

the compass. This correction was not effectual, because the magnetic

forces of the plate and of the ship do not change their direction

and value according to the same law, with the change of position. I

have further stated that Mr. Airy devised other means of correcting

the error. I may add a few words on the subject; for the subject has

been further examined by Mr. Airy[25\B] and by others.

[Note 25\B: _Phil. Trans._ 1856.]

It appears, by mathematical reasoning, that the magnetic effect of

the iron in a ship may be regarded as producing two kinds of

deviation which are added together;--a "polar-magnet deviation,"

which changes from positive to negative as the direction of the

ship's keel, in a horizontal revolution, passes from semicircle to

semicircle; and a "quadrantal deviation," which changes from

positive to negative as the keel turns from quadrant to quadrant.

The latter deviation may be remedied completely by a mass of

unmagnetized iron placed on a level {617} with the compass, either

in the athwartship line or in the fore-and-aft line, according to

circumstances. "The polar-magnet-deviation" may be corrected at _any

given place_ by a magnet or magnets, but the magnets thus applied at

one place will not always correct the deviation in another magnetic

latitude. For it appears that this deviation arises partly from a

magnetism inherent in the materials of the ship, not changing with

the change of magnetic position, and partly from the effect of

terrestrial magnetism upon the ship's iron. But the errors arising

from both sources may be remedied by adjusting, at a new locality,

the positions of the corrective magnets.

The inherent magnetism of the ship, of which I have spoken, may be

much affected by the position in which the ship was built; and may

change from time to time; for instance, by the effect of the

battering of the waves, and other causes. Hence it is called by Mr.

Airy "sub-permanent magnetism."

Another method of correcting the errors of a ship's compass has been

proposed, and is used to some extent; namely, by _swinging_ the ship

round (in harbor) to all points of azimuth, and thus constructing a

_Table of Compass Errors_ for that particular ship. But to this

method it is objected that the Table loses its value in a new

magnetic latitude much more than the correction by magnets does;

besides the inconveniences of steering a ship by a Table.

BOOK XIII.

VOLTAIC ELECTRICITY.

CHAPTER VII.

MAGNETO-ELECTRIC INDUCTION.

FARADAY'S discovery that, in combinations like those in which a

voltaic current was known to produce motion, motion would produce a

voltaic current, naturally excited great attention among the

scientific men of Europe. The general nature of his discovery was

communicated by letter[26\B] to M. Hachette at Paris, in December,

1831; and experiments having the like results were forthwith made by

MM. Becquerel and Ampère at Paris, and MM. Nobili and Antinori at

Florence.

[Note 26\B: _Ann. de Chimie_, vol. xlviii. (1831), p. 402.]

It was natural also that in a case in which the relations of space

which determine the results are so complicated, different

philosophers should look at them in different ways. There had been,

from the first discovery by Oersted of the effect of a voltaic

current upon a magnet, two rival methods of regarding the facts.

Electric and magnetic lines exert an effort to place themselves

transverse to each other (see chapter iv. of this Book), and (as I

have already said) two ways offered themselves of simplifying this

general truth:--to suppose an electric current made up of transverse

magnetic lines; or to suppose magnetic lines made up of transverse

electric currents. On either of these assumptions, the result was

expressed by saying that _like_ currents or lines (electric or

magnetic) tend to place themselves parallel; which is a law more

generally intelligible than the law of transverse position. Faraday

had adopted the former view; had taken the lines of magnetic force

for the fundamental lines of his system, and defined the direction

of the magneto-electric current of induction by the relation {619}

of the motion to these lines. Ampère, on the other hand, supposed

the magnet to be made up of transverse electric currents (chap.

vi.); and had deduced all the facts of electro-dynamical action,

with great felicity, from this conception. The question naturally

arose, in what manner, on this view, were the new facts of

magneto-electric induction by motion to be explained, or even

expressed?

Various philosophers attempted to answer this question. Perhaps the

form in which the answer has obtained most general acceptance is

that in which it was put by Lenz, who discoursed on the subject to

the Academy of St. Petersburg in 1833.[27\B] His general rule is to

this effect: when a wire moves in the neighborhood of an electric

current or a magnet, a current takes place in it, such as, existing

independently, would have produced a motion opposite to the actual

motion. Thus two parallel _forward_ currents move towards each

other:--hence if a current move towards a parallel wire, it produces

in it a _backward_ current. A moveable wire conducting a current

_downwards_ will move round the north pole of a magnet in the

direction N., W., S., E.:--hence if, when the wire have in it no

current, we move it in the direction N., W., S., E., we produce in

the wire an _upward_ current. And thus, as M. de la Rive

remarks,[28\B] in cases in which the mutual action of two currents

produces a limited motion, as attraction or repulsion, or a

deviation right or left, the corresponding magneto-electric

induction produces an instantaneous current only; but when the

electrodynamic action produces a continued motion, the corresponding

motion produces, by induction, a continued current.

[Note 27\B: _Acad. Petrop._ Nov. 29, 1833. _Pogg. Ann._ vol. xxxi.

p. 483.]

[Note 28\B: _Traité de l'Electricité_, vol. i. p. 441 (1854).]

Looking at this mode of stating the law, it is impossible not to

regard this effect as a sort of reaction; and accordingly, this view

was at once taken of it. Professor Ritchie said, in 1833, "The law

is founded on the universal principle that action and reaction are

equal." Thus, if voltaic electricity induce magnetism under certain

arrangements, magnetism will, by similar arrangements, react on a

conductor and induce voltaic electricity.[29\B]

[Note 29\B: On the Reduction of Mr. Faraday's discoveries in

Magneto-electric Induction to a General Law. _Trans._ of R. S. in

_Phil. Mag._ N.S. vol. iii. 37, and vol. iv. p. 11. In the second

edition of this history I used the like expressions.]

There are still other ways of looking at this matter. I have

elsewhere pointed out that where polar properties co-exist, they are

{620} generally found to be connected,[30\B] and have illustrated

this law in the case of electrical, magnetical, and chemical

polarities. If we regard motion backwards and forwards, to the right

and the left, and the like, as _polar_ relations, we see that

magneto-electric induction gives us a new manifestation of connected

polarities.

[Note 30\B: _Phil. Ind. Sc._ B. v. c. ii.]

_Diamagnetic Polarity_.

But the manifestation of co-existent polarities which are brought into

view in this most curious department of nature is not yet exhausted by

those which we have described. I have already spoken (chap. **vii.) of

Dr. Faraday's discovery that there are diamagnetic as well as magnetic

bodies; bodies which are repelled by the pole of a magnet, as well as

bodies which are attracted. Here is a new opposition of properties.

What is the exact definition of this opposition in connexion with

other polarities? To this, at present, different philosophers give

different answers. Some say that diamagnetism is completely the

opposite of ordinary magnetism, or, as Dr. Faraday has termed it for

the sake of distinction, of _paramagnetism_. They say that as a north

pole of a magnet gives to the neighboring extremity of a piece of soft

iron a south pole, so it gives to the neighboring extremity of a piece

of bismuth a north pole, and that the bismuth becomes for a time an

inverted magnet; and hence, arranges itself across the line of

magnetised force, instead of along it. Dr. Faraday himself at first

adopted this view;[31\B] but he now conceives that the bismuth is not

made polar, but is simply repelled by the magnet; and that the

transverse position which it assumes, arises merely from its elongated

form, each end trying to recede as far as possible from the repulsive

pole of the magnet.

[Note 31\B: Faraday's _Researches_, Art. 2429, 2430.]

Several philosophers of great eminence, however, who have examined

the subject with great care, adhere to Dr. Faraday's first view of

the nature of Diamagnetism--as W. Weber,[32\B] Plücker, and Mr.

Tyndall among ourselves. If we translate this view into the language

of Ampère's theory, it comes to this:--that as currents are induced

in iron and magnetics parallel to those existing in the inducing

magnet or battery wire; so in bismuth, heavy glass, and other

diamagnetic bodies, the currents induced are in the contrary {621}

directions:--these hypothetical currents being in non-conducting

diamagnetic, as in magnetic bodies, not in the mass, but round the

particles of the matter.

[Note 32\B: Poggendorf's _Ann. Jou._ 1848.]

_Magneto-optic Effects and Magnecrystallic Polarity._

Not even yet have we terminated the enumeration of the co-existent

polarities which in this province of nature have been brought into

view. Light has polar properties; the very term _polarization_ is

the record of the discovery of these. The forces which determine the

crystalline forms of bodies are of a polar nature: crystalline

forms, when complete, may be defined as those forms which have a

certain degree of symmetry in reference to opposite poles. Now has

this optical and crystalline polarity any relation to the electrical

polarity of which we have been speaking?

However much we might be disposed beforehand to conjecture that

there is some relation between these two groups of polar properties,

yet in this as in the other parts of this history of discoveries

respecting polarities, no conjecture hits the nature of the

relation, such as experiment showed it to be. In November, 1846,

Faraday announced the discovery of what he then called "the action

of magnets on light." But this action was manifested, not on light

directly, but on light passing through certain kinds of glass.[33\B]

When this glass, subjected to the action of the powerful magnets

which he used, transmitted a ray of light parallel to the line of

magnetic force, an effect was produced upon the light. But of what

nature was this effect? When light was ordinary light, no change in

its condition was discoverable. But if the light were light

polarized in any plane, the plane of polarization was turned round

through a certain angle while the ray passed through the glass:--a

greater angle, in proportion as the magnetic force was greater, and

the thickness of the glass greater.

[Note 33\B: Silicated borate of lead. See _Researches_, § 2151, &c.

Also flint glass, rock salt, water (2215).]

A power in some respects of this kind, namely, a power to rotate the

plane of polarization of a ray passing through them, is possessed by

some bodies in their natural state; for instance, quartz crystals,

and oil of turpentine. But yet, as Dr. Faraday remarks,[34\B] there

is a great difference in the two cases. When polarized rays pass

through oil of turpentine, in whatever direction they pass, they all

of them have their {622} plane of polarization rotated in the same

direction; that is, all to the right or all to the left; but when a

ray passes through the heavy glass, the power of rotation exists

only in a plane perpendicular to the magnetic line, and its

direction as right or left-handed is reversed by reversing the

magnetic polarity.

[Note 34\B: _Researches_, Art. 2231.]

In this case, we have optical properties, which do not depend on

crystalline form, affected by the magnetic force. But it has also been

found that crystalline form, which is so fertile a source of optical

properties, affords indications of magnetic forces. In 1847, M.

Plücker,[35\B] of the University of Bonn, using a powerful magnetic

apparatus, similar to Faraday's, found that crystals in general are

magnetic, in this sense, that the axes of crystalline form tend to

assume a certain position with reference to the magnetic lines of

force. The possession of one optic axis or of two is one of the broad

distinctions of the different crystalline forms: and using this

distinction, M. Plücker found that a crystal having a single optic

axis tends to place itself with this axis transverse to the magnetic

line of force, as if its optic axis were repelled by each magnetic

pole; and crystals with two axes act as if each of these axes were

repelled by the magnetic poles. This force is independent of the

magnetic or diamagnetic character of the crystal; and is a directive,

more properly than an attractive or repulsive force.

[Note 35\B: Taylor's _Scientific Memoirs_, vol. v.]

Soon afterwards (in 1848) Faraday also discovered[36\B] an effect of

magnetism depending on crystalline form, which at first sight appeared

to be different from the effects observed by M. Plücker. He found that

a crystal of bismuth, of which the form is nearly a cube, but more

truly a rhombohedron with one diagonal a little longer than the

others, tends to place itself with this diagonal in the direction of

the lines of magnetic force. At first he conceived[37\B] the

properties thus detected to be different from those observed by M.

Plücker; since in this case the force of a crystalline axis is axial,

whereas in those, it was equatorial. But a further consideration of

the subject, led him[38\B] to a conviction that these forces must be

fundamentally identical: for it was easy to conceive a combination of

bismuth crystals which would behave in the magnetic field as a crystal

of calcspar does; or a combination of calcspar crystals which would

behave as a crystal of bismuth does.

[Note 36\B: _Researches_, Art. 2454, &c.]

[Note 37\B: Art. 2469.]

[Note 38\B: Art 2593, 2601.]

And thus we have fresh examples to show that the Connexion of

coexistent Polarities is a thought deeply seated in the minds of the

{623} profoundest and most sagacious philosophers, and perpetually

verified and illustrated, by unforeseen discoveries in unguessed

forms, through the labors of the most skilful experimenters.

_Magneto-electric Machines._

The discovery that a voltaic wire moved in presence of a magnet, has

a current generated in it, was employed as the ground of the

construction of machines to produce electrical effects. In Saxton's

machine two coils of wire including a core of soft iron revolved

opposite to the ends of a horseshoe magnet, and thus, as the two

coils came opposite to the N. and S. and to the S. and N. poles of

the magnet, currents were generated alternately in the wires in

opposite directions. But by arranging the connexions of the ends of

the wires, the successive currents might be made to pass in

corresponding directions. The alternations or successions of

currents in such machines are governed by a contrivance which

alternately interrupts and permits the action; this contrivance has

been called a _rheotome_. Clarke gave a new form to a machine of the

same nature as Saxton's. But the like effect may be produced by

using an electro-magnet instead of a common magnet. When this is

done, a current is produced which by induction produces a current in

another wire, and the action is alternately excited and interrupted.

When the inducing current is interrupted, a momentary current _in an

opposite direction_ is produced in the induced wire; and when this

current stops, it produces in the inducing wire a current _in the

original direction_, which may be adjusted so as to reinforce the

resumed action of the original current. This was pointed out by M.

De la Rive in 1843.[39\B] Machines have been constructed on such

principles by him and others. Of such machines the most powerful

hitherto known is that constructed by M. Ruhmkorff. The effects of

this instrument are exceedingly energetic.

[Note 39\B: _Traité de l'Elect._ i. 391.]

_Applications of Electrodynamic Discoveries._

The great series of discoveries of which I have had to speak have

been applied in many important ways to the uses of life. The

_Electric Telegraph_ is one of the most remarkable of these. By

wires extended to the most distant places, the electric current is

transmitted {624} thither in an imperceptible time; and by means of

well-devised systems of operation, is made to convey from man to man

words, which are now most emphatically "winged words." In the most

civilised states such wires now form a net-work across the land,

which is familiar to our thoughts as the highway is to our feet; and

wide seas have such pathways of human thought buried deep in their

waves from shore to shore. Again, by using the chemical effects of

electrodynamic action, of which we shall have to speak in the next

Book, a new means has been obtained of copying, with an exactness

unattainable before, any forms which art or nature has produced, and

of covering them with a surface of metal. The _Electrotype Process_

is now one of the great powers which manufacturing art employs.

But these discoveries have also been employed in explaining natural

phenomena, the causes of which had before been altogether

inscrutable. This is the case with regard to the diurnal variation

of the magnetic needle; a fact which as to its existence is

universal in all places, and which yet is so curiously diverse in

its course at different places. Dr. Faraday has shown that some of

the most remarkable of these diversities, and probably all, seem to

be accounted for by the different magnetic effects of air at

different temperatures: although, as I have already said, **(Book

xii.) the discovery of a decennial period in the diurnal changes of

magnetic declination shows that any explanation of those changes

which refers them to causes existing in the atmosphere must be very

incomplete.[40\B]

[Note 40\B: _Researches_, Art. 2892.]

BOOK XIV.

CHEMISTRY.

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.

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.

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.]

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._)

CHAPTER VII.

ANIMAL MORPHOLOGY.

THE subject of Animal Morphology has recently been expanded into a

form strikingly comprehensive and systematic by Mr. Owen; and

supplied by him with a copious and carefully-chosen language; which

in his hands facilitates vastly the comparison and appreciation of

the previous labors of physiologists, and opens the way to new

truths and philosophical generalizations. Though the steps which

have been made had been prepared by previous anatomists, I will

borrow my view of them mainly from him; with the less scruple,

inasmuch as he has brought into full view the labors of his

predecessors.

I have stated in the History that the skeletons of all vertebrate

animals are conceived to be reducible to a single Type, and the

skull reducible to a series of vertebræ. But inasmuch as this

reduction includes not only a detailed correspondence of the bones

of man with those of beasts, but also with those of birds, fishes,

and reptiles, it may easily be conceived that the similarities and

connexions are of a various and often remote kind. The views of such

relations, held by previous Comparative Anatomists, have led to the

designations of the bones of animals which have been employed in

anatomical descriptions; and these designations having been framed

and adopted by anatomists looking at the subject from different

sides, and having different views of analogies and relations, have

been very various and unstable; besides being often of cumbrous

length and inconvenient form.

The corresponding parts in different animals are called _homologues_,

{639} a term first applied to anatomy by the philosophers of Germany;

and this term Mr. Owen adopts, to the exclusion of terms more loosely

denoting identity or similarity. And the Homology of the various bones

of vertebrates having been in a great degree determined by the labors

of previous anatomists, Mr. Owen has proposed names for each of the

bones: the condition of such names being, that the homologues in all

vertebrates shall be called by the same name, and that these names

shall be founded upon the terms and phrases in which the great

anatomists of the 16th, 17th, and 18th centuries expressed the results

of their researches respecting the human skeleton. These names, thus

selected, so far as concerned the bones of the Head of Fishes, one of

the most difficult cases of this Special Homology, he published in a

Table,[44\B] in which they were compared, in parallel columns, with

the names or phrases used for the like purpose by Cuvier, Agassiz,

Geoffroy, Hallman, Sœmmering, Meckel, and Wagner. As an example of the

considerations by which this selection of names was determined, I may

quote what he says with regard to one of these bones of the skull.

[Note 44\B: _Lectures on Vertebrates_. 1846, p. 158. And _On the

Archetype and Homologies of the Vertebrate Skeleton_. 1848, p. 172.]

"With regard to the 'squamosal' (_squamosum_. Lat. pars squamosa

ossis temporis.--Sœmmering), it might be asked why the term

'temporal' might not be retained for this bone. I reply, because

that term has long been, and is now universally, understood in human

anatomy to signify a peculiarly anthropotomical coalesced congeries

of bones, which includes the 'squamosal' together with the

'petrosal,' the 'tympanic,' the 'mastoid,' and the 'stylohyal.' It

seems preferable, therefore, to restrict the signification of the

term 'temporal' to the whole (in Man) of which the 'squamosal' is a

part. To this part Cuvier has unfortunately applied the term

'temporal' in one class, and 'jugal' in another; and he has also

transferred the term 'temporal' to a third equally distinct bone in

fishes; while to increase the confusion M. Agassiz has shifted the

name to a fourth different bone in the skull of fishes. Whatever,

therefore, may be the value assigned to the arguments which will be

presently set forth, as to the special homologies of the 'pars

squamosa ossis temporis,' I have felt compelled to express the

conclusion by a definite term, and in the present instance, have

selected that which recalls the best accepted anthropomorphical

designation of the part; although 'squamosal' must be understood and

applied in an arbitrary sense; and not as descriptive of a

scale-like {640} form; which in reference to the bone so called, is

rather its exceptional than normal figure in the vertebrate series."

The principles which Mr. Owen here adopts in the selection of names

for the parts of the skeleton are wise and temperate. They agree

with the aphorisms concerning the language of science which I

published in the _Philosophy of the Inductive Sciences_; and Mr.

Owen does me the great honor of quoting with approval some of those

Aphorisms. I may perhaps take the liberty of remarking that the

system of terms which he has constructed, may, according to our

principles, be called rather a _Terminology_ **than a

_Nomenclature_: that is, they are analogous more nearly to the

_terms_ by which botanists describe the parts and organs of plants,

than to the _names_ by which they denote genera and species. As we

have seen in the History, plants as well as animals are subject to

morphological laws; and the names which are given to organs in

consequence of those laws are a part of the Terminology of the

science. Nor is this distinction between Terminology and

Nomenclature without its use; for the rules of prudence and

propriety in the selection of words in the two cases are different.

The Nomenclature of genera and species may be arbitrary and casual,

as is the case to a great extent in Botany and in Zoology,

especially of fossil remains; names being given, for instance,

simply as marks of honor to individuals. But in a Terminology, such

a mode of derivation is not admissible: some significant analogy or

idea must be adopted, at least as the origin of the name, though not

necessarily true in all its applications, as we have seen in the

case of the "squamosal" just quoted. This difference in the rules

respecting two classes of scientific words is stated in the

_Aphorisms_ xiii. and xiv. _concerning the Language of Science_.

Such a Terminology of the bones of the skeletons of all vertebrates

as Mr. Owen has thus propounded, cannot be otherwise than an immense

acquisition to science, and a means of ascending from what we know

already to wider truths and new morphological doctrines.

With regard to one of these doctrines, the resolution of the human

head into vertebræ, Mr. Owen now regards it as a great truth, and

replies to the objections of Cuvier and M. Agassiz, in detail.[45\B]

He gives a Table in which the Bones of the Head are resolved into

four vertebræ, which he terms the Occipital, Parietal, Frontal, and

Nasal Vertebra, respectively. These four vertebræ agree in general

with what Oken called the Ear-vertebra, the Jaw-vertebra, the

Eye-vertebra, and {641} the Nose-vertebra, in his work _On the

Signification of the Bones of the Skull_, published in 1807: and in

various degrees, with similar views promulgated by Spix (1815),

Bojanus (1818), Geoffroy (1824), Carus **(1828). And I believe that

these views, bold and fanciful as they at first appeared, have now

been accepted by most of the principal physiologists of our time.

[Note 45\B: _Archetype and Homologies of the Vertebrate Skeleton_.

1848, p. 141.]

But another aspect of this generalization has been propounded among

physiologists; and has, like the others, been extended,

systematized, and provided with a convenient language by Mr. Owen.

Since animal skeletons are thus made up of vertebræ and their parts

are to be understood as developements of the parts of vertebræ,

Geoffroy (1822), Carus (1828), Müller (1834), Cuvier (1836), had

employed certain terms while speaking of such developements; Mr.

Owen in the _Geological Transactions_ in 1838, while discussing the

osteology of certain fossil Saurians, used terms of this kind, which

are more systematic than those of his predecessors, and to which he

has given currency by the quantity of valuable knowledge and thought

which he has embodied in them.

According to his Terminology,[46\B] a vertebra, in its typical

completeness, consists of a central part or _centrum_; at the back

of this, two plates (the _neural apophyses_) and a third outward

projecting piece (the _neural spine_), which three, with the

centrum, form a canal for the spinal marrow; at the front of the

centrum two other plates (the _hæmal apophyses_) and a projecting

piece, forming a canal for a vascular trunk. Further lateral

elements (_pleuro-apophyses_) and other projections, are in a

certain sense dependent on these principal bones; besides which the

vertebra may support _diverging appendages_. These parts of the

vertebra are fixed together, so that a vertebra is by some

anatomists described as a single bone; but the parts now mentioned

are usually developed from distinct and independent centres, and are

therefore called by Mr. Owen "autogenous" elements.

[Note 46\B: _Archetype and Homologies of the Vertebrate Skeleton_.

1848, p. 81.]

The _General_ Homology of the vertebral skeleton is the reference of

all the parts of a skeleton to their true types in a series of

vertebræ: and thus, as _special_ homology refers all the parts of

skeletons to a given type of skeleton, say that of Man, _general_

homology refers all the parts of every skeleton, say that of Man, to

the parts of a series of Vertebræ. And thus as Oken propounded his

views of the Head as a resolution of the Problem of _the

Signification of the Bones of the Head_, {642} so have we in like

manner, for the purposes of General Homology, to solve the Problem

of _the Signification of Limbs_. The whole of the animal being a

string of vertebræ, what are arms and legs, hands and paws, claws

and fingers, wings and fins, and the like? This inquiry Mr. Owen has

pursued as a necessary part of his inquiries. In giving a public

lecture upon the subject in 1849,[47\B] he conceived that the phrase

which I have just employed would not be clearly apprehended by an

English Audience, and entitled his Discourse "On the _Nature_ of

Limbs:" and in this discourse he explained the modifications by

which the various kinds of limbs are derived from their rudiments in

an archetypal skeleton, that is, a mere series of vertebræ without

head, arms, legs, wings, or fins.

[Note 47\B: _On the Nature of Limbs_, a discourse delivered at a

Meeting of the Royal Institution, 1849.]

_Final Causes_

It has been mentioned in the History that in the discussions which

took place concerning the Unity of Plan of animal structure, this

principle was in some measure put in opposition to the principle of

Final Causes: Morphology was opposed to Teleology. It is natural to

ask whether the recent study of Morphology has affected this

antithesis.

If there be advocates of Final Causes in Physiology who would push

their doctrines so far as to assert that every feature and every

relation in the structure of animals have a purpose discoverable by

man, such reasoners are liable to be perpetually thwarted and

embarrassed by the progress of anatomical knowledge; for this

progress often shows that an arrangement which had been explained

and admired with reference to some purpose, exists also in cases

where the purpose disappears; and again, that what had been noted as

a special teleological arrangement is the result of a general

morphological law. Thus to take an example given by Mr. Owen: that

the ossification of the head originates in several centres, and thus

in its early stages admits of compression, has been pointed out as a

provision to facilitate the birth of viviparous animals; but our

view of this provision is disturbed, when we find that the same mode

of the formation of the bony framework takes place in animals which

are born from an egg. And the number of points from which

ossification begins, depends in a wider sense on the general

homology of the animal frame, according to which each part is

composed of a certain number of autogenous vertebral elements. In

this {643} way, the admission of a new view as to Unity of Plan will

almost necessarily displace or modify some of the old views

respecting Final Causes.

But though the view of Final Causes is displaced, it is not

obliterated; and especially if the advocate of Purpose is also ready

to admit visible correspondences which have not a discoverable

object, as well as contrivances which have. And in truth, how is it

possible for the student of anatomy to shut his eyes to either of

these two evident aspects of nature? The arm and hand of man are

made for taking and holding, the wing of the sparrow is made for

flying; and each is adapted to its end with subtle and manifest

contrivance. There is plainly Design. But the arm of man and the

wing of the sparrow correspond to each other in the most exact

manner, bone for bone. Where is the Use or the Purpose of this

correspondence? If it be said that there may be a purpose though we

do not see it, that is granted. But Final Causes _for us_ are

contrivances of which _we see_ the end; and nothing is added to the

evidence of Design by the perception of a unity of plan which in no

way tends to promote the design.

It may be said that the design appears in the modification of the

plan in special ways for special purposes;--that the vertebral plan

of an animal being given, the fore limbs are modified in Man and in

Sparrow, as the nature and life of each require. And this is truly

said; and is indeed the truth which we are endeavoring to bring into

view:--that there are in such speculations, two elements; one given,

the other to be worked out from our examination of the case; the

_datum_ and the _problem_; the homology and the teleology.

Mr. Owen, who has done so much for the former of these portions of

our knowledge, has also been constantly at the same time

contributing to the other. While he has been aiding our advances

towards the Unity of Nature, he has been ever alive to the

perception of an Intelligence which pervades Nature. While his

morphological doctrines have moved the point of view from which he

sees Design, they have never obscured his view of it, but, on the

contrary, have led him to present it to his readers in new and

striking aspects. Thus he has pointed out the final purposes in the

different centres of ossification of the long bones of the limbs of

mammals, and shown how and why they differ in this respect from

reptiles (_Archetype_, p. 104). And in this way he has been able to

point out the insufficiency of the rule laid down both by Geoffroy

St. Hilaire and Cuvier, for ascertaining the true number of bones in

each species. {644}

Final Causes, or Evidences of Design, appear, as we have said, not

merely as contrivances for evident purposes, but as modifications of

a given general Plan for special given ends. If the general Plan be

discovered after the contrivance has been noticed, the discovery may

at first seem to obscure our perception of Purpose; but it will soon

be found that it merely transfers us to a higher point of view. The

adaptation of the Means to the End remains, though the Means are

parts of a more general scheme than we were aware of. No

generalization of the Means can or ought permanently to shake our

conviction of the End; because we must needs suppose that the

Intelligence which contemplates the End is an intelligence which can

see at a glance along a vista of Means, however long and complex.

And on the other hand, no special contrivance, however clear be its

arrangement, can be unconnected with the general correspondences and

harmonies by which all parts of nature are pervaded and bound

together. And thus no luminous teleological point can be

extinguished by homology; nor, on the other hand, can it be detached

from the general expanse of homological light.

The reference to Final Causes is sometimes spoken of as

unphilosophical, in consequence of Francis Bacon's comparison of

Final Causes in Physics to Vestal Virgins devoted to God, and

barren. I have repeatedly shown that, in Physiology, almost all the

great discoveries which have been made, have been made by the

assumption of a purpose in animal structures. With reference to

Bacon's simile, I have elsewhere said that if he had had occasion to

develope its bearings, full of latent meaning as his similes so

often are, he would probably have said that to those Final Causes

barrenness was no reproach, seeing they ought to be not the Mothers

but the Daughters of our Natural Sciences; and that they were

barren, not by imperfection of their nature, but in order that they

might be kept pure and undefiled, and so fit ministers in the temple

of God. I might add that in Physiology, if they are not Mothers,

they are admirable Nurses; skilful and sagacious in perceiving the

signs of pregnancy, and helpful in bringing the Infant Truth into

the light of day.

There is another aspect of the doctrine of the Archetypal Unity of

Composition of Animals, by which it points to an Intelligence from

which the frame of nature proceeds; namely this:--that the Archetype

of the Animal Structure being of the nature of an _Idea_, implies a

mind in which this Idea existed; and that thus Homology itself

points the way to the Divine Mind. But while we acknowledge the full

{645} value of this view of theological bearing of physiology, we

may venture to say that it is a view quite different from that which

is described by speaking of "Final Causes," and one much more

difficult to present in a lucid manner to ordinary minds.

BOOK XVIII.

GEOLOGY.

WITH regard to Geology, as a Palætiological Science, I do not know

that any new light of an important kind has been thrown upon the

general doctrines of the science. Surveys and examinations of

special phenomena and special districts have been carried on with

activity and intelligence; and the animals of which the remains

people the strata, have been reconstructed by the skill and

knowledge of zoologists:--of such reconstructions we have, for

instance, a fine assemblage in the publications of the

Palæontological Society. But the great questions of the manner of

the creation and succession of animal and vegetable species upon the

earth remain, I think, at the point at which they were when I

published the last edition of the History.

I may notice the views propounded by some chemists of certain

bearings of Mineralogy upon Geology. As we have, in mineral masses,

organic remains of former organized beings, so have we crystalline

remains of former crystals; namely, what are commonly called

_pseudomorphoses_--the shape of one crystal in the substance of

another. M. G. Bischoff[48\B] considers the study of pseudomorphs as

important in geology, and as frequently the only means of tracing

processes which have taken place and are still going on in the

mineral kingdom.

[Note 48\B: _Chemical and Physical Geology_.]

I may notice also Professor Breithaupt's researches on the order of

succession of different minerals, by observing the mode in which

they occur and the order in which different crystals have been

deposited, promise to be of great use in following out the

geological changes which the crust of the globe has undergone. (_Die

Paragenesis der Mineralien_. Freiberg. 1849.)

In conjunction with these may be taken M. de Senarmont's experiments

on the formation of minerals in veins; and besides Bischoff's {647}

_Chemical Geology_, Sartorius von Walterhausen's Observations on the

occurrence of minerals in Amygdaloid.

As a recent example of speculations concerning Botanical

Palætiology, I may give Dr. Hooker's views of the probable history

of the Flora of the Pacific.

In speculating upon this question, Dr. Hooker is led to the

discussion of geological doctrines concerning the former continuity

of tracts of land which are now separate, the elevation of low lands

into mountain ranges in the course of ages, and the like. We have

already seen, in the speculations of the late lamented Edward

Forbes, (see Book xviii. chap. vi. of this History,) an example of a

hypothesis propounded to account for the existing Flora of England:

a hypothesis, namely, of a former Connexion of the West of the

British Isles with Portugal, of the Alps of Scotland with those of

Scandinavia, and of the plains of East Anglia with those of Holland.

In like manner Dr. Hooker says (p. xxi.) that he was led to

speculate on the possibility of the plants of the Southern Ocean

being the remains of a Flora that had once spread over a larger and

more continuous tract of land than now exists in the ocean; and that

the peculiar Antarctic genera and species may be the vestiges of a

Flora characterized by the predominance of plants which are now

scattered throughout the Southern islands. He conceives this

hypothesis to be greatly supported by the observations and

reasonings of Mr. Darwin, tending to show that such risings and

sinkings are in active progress over large portions of the

continents and islands of the Southern hemisphere: and by the

speculations of Sir C. Lyell respecting the influence of climate on

the migrations of plants and animals, and the influence of

geological changes upon climate.

In Zoology I may notice (following Mr. Owen)[49\B] recent

discoveries of the remains of the animals which come nearest to man

in their structure. At the time of Cuvier's death, in 1832, no

evidence had been obtained of fossil Quadrumana; and he supposed

that these, as well as Bimana, were of very recent introduction.

Soon after, in the oldest (eocene) tertiary deposits of Suffolk,

remains were found proving the existence of a monkey of the genus

Macacus. In the Himalayan tertiaries were found petrified bones of a

Semnopithecus; in Brazil, remains of an extinct platyrhine monkey of

great size; and lastly, in the middle tertiary series of the South

of France, was discovered a fragment of the jaw of the long-armed

ape (_Hylobates_). But no fossil human {648} remains have been

discovered in the regularly deposited layers of any divisions (not

even the pleiocene) of the tertiary series; and thus we have evidence

that the placing of man on the earth was the last and peculiar act

of Creation.

[Note 49\B: _Brit. Asso._ 1854, p. 112.]

THE END.

Transcriber's Notes

Whewell's book was originally published in 3 volumes in London in

1837. A second edition appeared in 1847, and a third in 1857. A

2-volume version of the 3rd edition was published in New York in 1858,

reprinted 1875. This Project Gutenberg text, combining both volumes

in sequence, was derived from the 1875 version, relying upon resources

kindly provided by the Internet Archive.

Three items have been added to the Contents of the First Volume;

they are marked off by ~ ~, as are any other additions to the text.

Printed page numbers have been transcribed in { }; pages without a

printed number have been indicated by {{ }}. Where words were

hyphenated across pages, the number has been placed before the word.

Fractions have been transcribed as numerator/denominator, occasionally

using parentheses to disambiguate. The original sometimes has

numerator over a line with denominator below, at other times numerator

hyphen denominator. Superscripted characters are marked by a ^ before

the character.

Footnotes in the original text were numbered by chapter; here they

have been numbered by Book (the number of which is given after a \,

for the two appendices to the 3rd edition A has been used for volume

1, B for volume 2). They are placed after the paragraph in which

they occur, and are transcribed [Note m\n: ...]. Footnote anchors

are transcribed [m\n]. All other square brackets are in the original

text.

One difficult item is the use of numbers within a ring as names of

asteroids; here the numbers are in ( ).

Corrections to the text have been marked with **. They are listed

below, and were usually confirmed by reference to English printings

of the text. Inconsistencies, especially with respect to accents and

formatting, are numerous and have in general not been adjusted, though

Greek quotations have been checked against other versions where

available. Nor have Whewell's unbalanced quotation marks been

modernised. The English versions have been used to restore Whewell's

"gesperrt" emphases in some Greek passages.

Location 1875 Text Correction

Vol. 1

p. 25 Cruikshanks Cruickshank

p. 30 19 65

p. 30 : ;

p. 33 (thrice) 184 182

p. 36 184 182

p. 71 Arisotelians Aristotelians

p. 75 "

p. 79 σερματικοὶ σπερματικοὶ

p. 101 "

note 1\2 6 7

p. 175 ecliptical elliptical

note 1\4 iv. vi.

note 75\4 Summæ Summa

note 10\5 iii. iv.

p. 271 (twice) Mastlin Mæstlin

p. 282 _Dialogo "_Dialogo

p. 284 semil semel

p. 287 endeaver endeavor

note 7\6 1. i.

note 8\6 Dial. i. p. 40. p. 141.

note 9\6 _Speculutionum _Speculationum

p. 325 Gualtier Gualter

p. 341 and 342 Marsenne Mersenne

p. 374 of

p. 377 prependicularity perpendicularity

p. 403 "

note 30\7 Cosmotheros Cosmotheoros

p. 415 _casual_ _causal_

p. 416 )

p. 419 ]

p. 431 _a_ a

note 69\7 1453 1753

note 84\7 Ast. Ass.

p. 463 Philosphical Philosophical

p. 471 ]

p. 564 prevalance prevalence

Vol. 2

p. 50 Ὑφιφάνη Ὑψιφάνη

ἄρισπον ἄριστον

οὔδιον εὔδιον

p. 84 ]

p. 85 viii. vii.

p. 115 1853 1823

p. 149 , .

p. 162 Footnote number missing in text

p. 201 stream steam

p. 213 and note 39\11 same number as the preceding note

p. 240 Cruikshanks Cruickshank

note 18\13 Mass-bestimmengen Mass-bestimmungen

p. 264 in is

note 11\14 _Stahl Stahl

p. 295 the _the

note 78\14 the entire text of this note is missing

p. 301 lecture lectures

note 87\14 96. 963.

note 92\14 153 853

p. 330 Angels Angles

p. 336 given giving

p. 343 "

p. 394 Surien Surian

p. 411 _Couérs Elmentaire_ _Cours Elémentaire_

note 136\16 Εἴδην Εἴδη

p. 450 dependance dependence

p. 457 sucking-beasts suckling-beasts

note 80\17 ählich ähnlich

note 89\17 229 129

p. 477 osseuze osseuse

note 119\17 229 299*

p. 508 Lythophylaccii Lythophylacii

p. 511 Stukely Stukeley

note 18\18 Géognastique Géognostique

p. 513 Sabapennine Sub-Apennine

p. 514 Schlotheim Schlottheim

p. 530 , ( ,)

p. 556 Poissons Poisson's

p. 620 iv. vii.

p. 624 [ (

p. 628 in (not italicised in text)

p. 630 Nordenskiold's Nordenskiöld's

p. 638 390 474

p. 640 then than

p. 641 1828 (1828)

* This is the page number given in the English edition. In the only

version of the text referred to that I have found, the quotation is

in a footnote on page 352 of the second edition (1805); the note

was not in the first edition.

History of the inductive sciences, from the earliest to the present time · 第 23 / 23 章

M. Wertheim also employed the vibrations of rods of steel and other