1st. Nothing is more rare than affections of the mass of the

brain; nothing is more common than inflammation of the _tunica

arachnoides_ that covers it. 2d. Oftentimes one membrane of the

eye only is affected, the others preserving their ordinary degree of

vitality. 3d. In convulsions or paralysis of the muscles of the larynx,

the mucous surface is unaffected; and on the other hand, the muscles

perform their functions as usual in catarrhs of this surface. Both

these affections are foreign to the cartilages, and _vice versa_.

4th. We observe a variety of different alterations in the texture

of the pericardium, but hardly ever in that of the heart itself; it

remains sound while the other is inflamed. The ossification of the

common membrane of the red blood does not extend to the neighboring

textures. 5th. When the membrane of the bronchia is the seat of

catarrh, the pleura is hardly affected at all, and reciprocally in

pleurisy the first is scarcely ever altered. In peripneumonia, when an

enormous infiltration in the dead body shows the excessive inflammation

that has existed during life in the pulmonary texture, the serous and

mucous surfaces often appear not to have been affected. Those who open

dead know that they are frequently healthy in incipient phthisis.

6th. We speak of a bad stomach, a weak stomach; this most commonly

should be understood as applying to the mucous surface only. Whilst

this secretes with difficulty the nutritive juices, without which

digestion is impaired, the serous surface exhales as usual its fluid,

the muscular coat continues to contract, etc. In ascites, in which

the serous surface exhales more lymph than in a natural state, the

mucous oftentimes performs its functions perfectly well, etc. 7th.

All authors have said much of the inflammation of the stomach, the

intestines, the bladder, etc. For myself, I believe that this disease

rarely ever affects at first the whole of any of these organs, except

in the case where poison or some other deleterious substance acts upon

them. There are for the mucous surface of the stomach and intestines,

acute and chronic catarrhs; for the peritoneum serous inflammations;

perhaps even for the layer of organic muscles that separates the two

membranes, there is a particular kind of inflammation, though we have

as yet hardly anything certain upon this point; but the stomach, the

intestines, and the bladder are not suddenly affected with these

three diseases. A diseased texture can affect those near it, but the

primitive affection seizes only upon one. I have examined a great

number of bodies in which the peritoneum was inflamed either upon the

intestines, the stomach, the pelvis, or universally; now very often

when this affection is chronic, and almost always when it is acute,

the subjacent organs remain sound. I have never seen this membrane

exclusively diseased upon one organ, while that of neighboring ones

remain untouched; its affection is propagated more or less remotely.

I know not why authors have hardly ever spoken of its inflammation,

and have placed to the account of the subjacent viscera that which

most often belongs only to this. There are almost as many cases

of peritonitis as of pleurisy, and yet while these last have been

particularly noticed the others are almost entirely overlooked.

Oftentimes that part of the peritoneum corresponding to an organ,

is much inflamed; we see it in the case of the stomach; we observe

especially after the suppression of the lochia or the menses, that it

is the portion that lines the pelvis that is first affected. But soon

the affection becomes more or less general; at least examinations after

death prove it satisfactorily. 8th. Certainly the acute or chronic

catarrh of the bladder, or womb even, has nothing in common with the

inflammation of that portion of the peritoneum corresponding with

these organs. 9th. Every one knows that diseases of the periosteum

have oftentimes no connection with the bone, and _vice versa_,

that frequently the marrow is for a long time affected, while both the

others remain sound. There is no doubt that the osseous, medullary

and fibrous textures have their peculiar affections which we shall

not confound with the idea we may form of the diseases of the bones.

The same can be said of the intestines, of the stomach, etc., in

relation to their mucous, serous, muscular textures, etc. 10th. Though

the muscular and tendinous textures are combined in a muscle, their

diseases are very different. 11th. You must not think that the synovial

is subject to the same diseases as the ligaments that surround it, etc.

I think the more we observe diseases, and the more we examine bodies,

the more we shall be convinced of the necessity of considering local

diseases, not under the relations of the compound organs, which are

rarely ever affected as a whole, but under that of their different

textures, which are almost always attacked separately.

When the phenomena of disease are sympathetic, they follow the same

laws as when they arise from a direct affection. Much has been said

of the sympathies of the stomach, the intestines, the bladder, the

lungs, etc. But it is impossible to form an idea of them, if they

are referred to the organ as a whole, separate from the different

textures. 1st. When in the stomach, the fleshy fibres contract by the

influence of another organ and produce vomiting, they alone receive

the influence, which is not extended either to the serous or mucous

surfaces; if it were, they would be the seat, the one of exhalation,

the other of sympathetic exhalation and secretion. 2d. It is certain

that when the action of the liver is sympathetically increased, so

that it pours out more bile, the portion of peritoneum that covers it

does not throw out more serum, because it is not affected by it. It

is the same of the kidney, the pancreas, etc. 3d. For the same reason

the gastric organs upon which the peritoneum is spread do not partake

of the sympathetic influences that it experiences. I shall say as much

of the lungs in relation to the pleura, the brain in relation to the

_tunica arachnoides_, the heart to the pericardium, etc. 4th. It

is undeniable that in all sympathetic convulsions, the fleshy texture

alone is affected, and that the tendinous is not so at all. 5th. What

has the fibrous membrane of the testicles in common with the sympathies

of its peculiar texture? 6th. No doubt a number of sympathetic pains

that we refer to the bones, are seated exclusively in the marrow.

I could cite many other examples to prove, that it is not this or that

organ that sympathizes as a whole, but only this or that texture in

the organs; besides, this an immediate consequence of the nature of

sympathies. In fact the sympathies are but aberrations of the vital

properties; now these properties vary according to each texture; the

sympathies of these textures then would do the same.

FOOTNOTES:

[Footnote 26: Translated from _Traité sur les Membranes_ (1800).]

XXIV

AMADEO AVOGADRO

1776-1856

_Avogadro, who continued the researches of Dalton and Gay-Lussac,

was born in Turin, Italy, June 9, 1776. In 1796, after receiving the

doctor’s degree in law from the University of Turin, he was employed

by the government for the following ten years. He began his work in

science in 1806 and three years later was made professor of physics at

Vercelli. In 1811 he announced his famous law. According to Merz, since

the time of Boyle “it had been known that equal volumes of different

gases under equal pressure change their volumes equally if the

pressure is varied equally, and it was also known that equal volumes

of different gases under equal pressure change their volumes equally

with equal rise of temperature. These facts suggested to Avogadro, and

almost simultaneously to Ampère, the very simple assumption that this

is owing to the fact that equal volumes of different gases contain an

equal number of the smallest independent particles of matter. This is

Avogadro’s celebrated hypothesis. It was the first step in the direct

physical verification of the atomic view of matter.”_

_In 1820 Avogadro became professor of physics at Turin University,

where he remained for many years. He died July 9, 1856._

THE MOLECULES IN GASES PROPORTIONAL TO THE VOLUMES[27]

I.

M. Gay-Lussac has shown in an interesting Memoir (_Mémoires de la

Société d’Arcueil_, Tome II.) that gases always unite in a very

simple proportion by volume, and that when the result of the union is a

gas, its volume also is very simply related to those of its components.

But the quantitative proportions of substances in compounds seem only

to depend on the relative number of molecules which combine, and on the

number of composite molecules which result. It must then be admitted

that very simple relations also exist between the volumes of gaseous

substances and the numbers of simple or compound molecules which form

them. The first hypothesis to present itself in this connection, and

apparently even the only admissible one, is the supposition that the

number of integral molecules in any gases is always the same for equal

volumes, or always proportional to the volumes. Indeed, if we were

to suppose that the number of molecules contained in a given volume

were different for different gases, it would scarcely be possible

to conceive that the law regulating the distance of molecules could

give in all cases relations so simple as those which the facts just

detailed compel us to acknowledge between the volume and the number

of molecules. On the other hand, it is very well conceivable that

the molecules of gases being at such a distance that their mutual

attraction cannot be exercised, their varying attraction for caloric

may be limited to condensing a greater or smaller quantity around

them, without the atmosphere formed by this fluid having any greater

extent in the one case than in the other, and, consequently, without

the distance between the molecules varying; or, in other words, without

the number of molecules contained in a given volume being different.

Dalton, it is true, has proposed a hypothesis directly opposed to

this, namely, that the quantity of caloric is always the same for the

molecules of all bodies whatsoever in the gaseous state, and that the

greater or less attraction for caloric only results in producing a

greater or less condensation of this quantity around the molecules,

and thus varying the distance between the molecules themselves. But

in our present ignorance of the manner in which this attraction of

the molecules for caloric is exerted, there is nothing to decide

us _a priori_ in favour of the one of these hypotheses rather

than the other; and we should rather be inclined to adopt a neutral

hypothesis, which would make the distance between the molecules and

the quantities of caloric vary according to unknown laws, were it not

that the hypothesis we have just proposed is based on that simplicity

of relation between the volumes of gases on combination, which would

appear to be otherwise inexplicable.

Setting out from this hypothesis, it is apparent that we have the means

of determining very easily the relative masses of the molecules of

substances obtainable in the gaseous state, and the relative number

of these molecules in compounds; for the ratios of the masses of the

molecules are then the same as those of the densities of the different

gases at equal temperature and pressure, and the relative number of

molecules in a compound is given at once by the ratio of the volumes

of the gases that form it. For example, since the numbers 1.10359 and

0.07321 express the densities of the two gases oxygen and hydrogen

compared to that of atmospheric air as unity, and the ratio of the two

numbers consequently represents the ratio between the masses of equal

volumes of these two gases, it will also represent on our hypothesis

the ratio of the masses of their molecules. Thus the mass of the

molecule of oxygen will be about 15 times that of the molecule of

hydrogen, or, more exactly, as 15.074 to 1. In the same way the mass

of the molecule of nitrogen will be to that of hydrogen as 0.96913 to

0.07321, that is, as 13, or more exactly 13.238, to 1. On the other

hand, since we know that the ratio of the volumes of hydrogen and

oxygen in the formation of water is 2 to 1, it follows that water

results from the union of each molecule of oxygen with two molecules of

hydrogen. Similarly, according to the proportions by volume established

by M. Gay-Lussac for the elements of ammonia, nitrous oxide, nitrous

gas, and nitric acid, ammonia will result from the union of one

molecule of nitrogen with three of hydrogen, nitrous oxide from one

molecule of oxygen with two of nitrogen, nitrous gas from one molecule

of nitrogen with one of oxygen, and nitric acid from one of nitrogen

with two of oxygen.

II.

There is a consideration which appears at first sight to be opposed to

the admission of our hypothesis with respect to compound substances.

It seems that a molecule composed of two or more elementary molecules

should have its mass equal to the sum of the masses of these molecules;

and that in particular, if in a compound one molecule of one substance

unites with two or more molecules of another substance, the number

of compound molecules should remain the same as the number of

molecules of the first substance. Accordingly, on our hypothesis when

a gas combines with two or more times its volume of another gas, the

resulting compound, if gaseous, must have a volume equal to that of

the first of these gases. Now, in general, this is not actually the

case. For instance, the volume of water in the gaseous state is, as

M. Gay-Lussac has shown, twice as great as the volume of oxygen which

enters into it, or, what comes to the same thing, equal to that of the

hydrogen instead of being equal to that of the oxygen. But a means

of explaining facts of this type in conformity with our hypothesis

presents itself naturally enough: we suppose, namely, that the

constituent molecules of any simple gas whatever (i. e., the molecules

which are at such a distance from each other that they cannot exercise

their mutual action) are not formed of a solitary elementary molecule,

but are made up of a certain number of these molecules united by

attraction to form a single one; and further, that when molecules of

another substance unite with the former to form a compound molecule,

the integral molecule which should result splits up into two or more

parts (or integral molecules) composed of half, quarter, &c., the

number of elementary molecules going to form the constituent molecule

of the first substance, combined with half, quarter, &c., the number of

constituent molecules of the second substance that ought to enter into

combination with one constituent molecule of the first substance (or,

what comes to the same thing, combined with a number equal to this last

of half-molecules, quarter-molecules, &c., of the second substance);

so that the number of integral molecules of the compound becomes

double, quadruple, &c., what it would have been if there had been no

splitting-up, and exactly what is necessary to satisfy the volume of

the resulting gas.

On reviewing the various compound gases most generally known, I only

find examples of duplication of the volume relatively to the volume of

that one of the constituents which combines with one or more volumes

of the other. We have already seen this for water. In the same way,

we know that the volume of ammonia gas is twice that of the nitrogen

which enters into it. M. Gay-Lussac has also shown that the volume of

nitrous oxide is equal to that of the nitrogen which forms part of

it, and consequently is twice that of the oxygen. Finally, nitrous

gas, which contains equal volumes of nitrogen and oxygen, has a

volume equal to the sum of the two constituent gases, that is to say,

double that of each of them. Thus in all these cases there must be a

division of the molecule into two; but it is possible that in other

cases the division might be into four, eight, &c. The possibility of

this division of compound molecules might have been conjectured _a

priori_; for otherwise the integral molecules of bodies composed

of several substances with a relatively large number of molecules,

would come to have a mass excessive in comparison with the molecules

of simple substances. We might therefore imagine that nature had some

means of bringing them back to the order of the latter, and the facts

have pointed out to us the existence of such means. Besides, there

is another consideration which would seem to make us admit in some

cases the division in question; for how could one otherwise conceive

a real combination between two gaseous substances uniting in equal

volumes without condensation, such as takes place in the formation of

nitrous gas? Supposing the molecules to remain at such a distance that

the mutual attraction of those of each gas could not be exercised,

we cannot imagine that a new attraction could take place between the

molecules of one gas and those of the other. But on the hypothesis

of division of the molecule, it is easy to see that the combination

really reduces two different molecules to one, and that there would be

contraction by the whole volume of one of the gases if each compound

molecule did not split up into two molecules of the same nature. M.

Gay-Lussac clearly saw that, according to the facts, the diminution of

volume on the combination of gases cannot represent the approximation

of their elementary molecules. The division of molecules on combination

explains to us how these two things may be made independent of each

other.

III.

Dalton, on arbitrary suppositions as to the most likely relative number

of molecules in compounds, has endeavoured to fix ratios between the

masses of the molecules of simple substances. Our hypothesis, supposing

it well founded, puts us in a position to confirm or rectify his

results from precise data, and, above all, to assign the magnitude of

compound molecules according to the volumes of the gaseous compounds,

which depend partly on the division of molecules entirely unsuspected

by this physicist.

Thus Dalton supposes that water is formed by the union of hydrogen and

oxygen, molecule to molecule. From this, and from the ratio by weight

of the two components, it would follow that the mass of the molecule of

oxygen would be to that of hydrogen as 7-1/2 to 1 nearly, or, according

to Dalton’s evaluation, as 6 to 1. This ratio on our hypothesis is,

as we saw, twice as great, namely, as 15 to 1. As for the molecule of

water, its mass ought to be roughly expressed by 15 + 2 = 17 (taking

for unity that of hydrogen), if there were no division of the molecule

into two; but on account of this division it is reduced to half, 8-1/2,

or more exactly 8.537, as may also be found directly by dividing the

density of aqueous vapour 0.625 (Gay-Lussac) by the density of hydrogen

0.0732. This mass only differs from 7, that assigned to it by Dalton,

by the difference in the values for the composition of water; so that

in this respect Dalton’s result is approximately correct from the

combination of two compensating errors,--the error in the mass of the

molecule of oxygen, and his neglect of the division of the molecule.

FOOTNOTES:

[Footnote 27: Translated from _Essai d’une manière de déterminer

les masses relatives des molécules élémentaires des corps,

et les proportions selon lesquelles elles entrent dans les

combinaisons_--_Journal de Physique_, (1811).]

XXV

SIR HUMPHREY DAVY

1778-1829

_Born December 17, 1778, in Cornwall, Sir Humphrey Davy was

apprenticed in 1794 to a surgeon-apothecary at Penzance in whose

service he became interested in chemistry. Made superintendent of a

hospital in 1798, he had opportunities for gaining acquaintance with

influential men who in turn recommended him to Count Rumford. Through

the latter’s assistance he was appointed lecturer on chemistry at the

newly-founded Royal Institution where, in spite of his unattractive

appearance, he gained considerable reputation. In 1807 he advanced a

theory which partly explained electrolysis; in the following year he

discovered strontium and magnesium; and in 1809, chlorine. In 1812 he

was knighted; and shortly after his marriage, in the same year, he

injured an eye while experimenting and was compelled to interrupt his

work for a short time. In 1815 he invented the safety-lamp used by

miners. In 1818 he was created a baronet, and was elected President

of the Royal Society in 1820. He died May 29, 1829, at Geneva,

Switzerland, at the age of fifty-one._

ON SOME NEW PHENOMENA OF CHEMICAL CHANGES PRODUCED BY ELECTRICITY[28]

_Read November 19, 1807._

INTRODUCTION.

In the Bakerian Lecture which I had the honour of presenting to the

Royal Society last year, I described a number of decompositions

and chemical changes produced in substances of known composition by

electricity, and I ventured to conclude from the general principles

on which the phenomena were capable of being explained, that the new

methods of investigation promised to lead to a more intimate knowledge

than had hitherto been obtained, concerning the true elements of bodies.

This conjecture, then sanctioned only by strong analogies, I am now

happy to be able to support by some conclusive facts. In the course of

a laborious experimental application of the powers of electro-chemical

analysis, to bodies which have appeared simple when examined by common

chemical agents, or which at least have never been decomposed, it has

been my good fortune to obtain new and singular results.

Such of the series of experiments as are in a tolerably mature state,

and capable of being arranged in a connected order, I shall detail

in the following sections, particularly those which demonstrate the

decomposition and composition of the fixed alkalies, and the production

of the new and extraordinary bodies which constitute their bases.

In speaking of novel methods of investigation, I shall not fear to be

minute. When the common means of chemical research have been employed,

I shall mention only results. A historical detail of the progress

of the investigation, of all the difficulties that occurred, and of

the manner in which they were overcome, and of all the manipulations

employed, would far exceed the limits assigned to this Lecture. It is

proper to state, however, that when general facts are mentioned, they

are such only as have been deduced from processes carefully performed

and often repeated.

ON THE METHODS USED FOR THE DECOMPOSITION OF THE FIXED ALKALIES

The researches I had made on the decomposition of acids, and of

alkaline and earthy neutral compounds, proved that the powers of

electrical decomposition were proportional to the strength of the

opposite electricities in the circuit, and to the conducting power and

degree of concentration of the materials employed.

In the first attempts, that I made on the decomposition of the fixed

alkalies, I acted upon aqueous solutions of potash and soda, saturated

at common temperatures, by the highest electrical power I could

command, and which was produced by a combination of Voltaic batteries

belonging to the Royal Institution, containing 24 plates of copper and

zinc of 12 inches square, 100 plates of 6 inches, and 150 of 4 inches

square, charged with solutions of alum and nitrous acid; but in these

cases, though there was a high intensity of action, the water of the

solutions alone was affected, and hydrogen and oxygen disengaged with

the production of much heat and violent effervescence.

The presence of water appearing thus to prevent any decomposition, I

used potash in igneous fusion. By means of a stream of oxygen gas from

a gasometer applied to the flame of a spirit lamp, which was thrown

on a platina spoon containing potash, this alkali was kept for some

minutes in a strong red heat, and in a state of perfect fluidity.

The spoon was preserved in communication with the positive side of

the battery of the power of 100 of 6 inches, highly charged; and the

connection from the negative side was made by a platina wire.

By this arrangement some brilliant phenomena were produced. The potash

appeared a conductor in a high degree, and as long as the communication

was preserved, a most intense light was exhibited at the negative wire,

and a column of flame, which seemed to be owing to the development of

combustible matter, arose from the point of contact.

When the order was changed, so that the platina spoon was made

negative, a vivid and constant light appeared at the opposite point:

there was no effect of inflammation round it; but aeriform globules,

which inflamed in the atmosphere, rose through the potash.

The platina, as might have been expected, was considerably acted upon;

and in the cases when it had been negative, in the highest degree.

The alkali was apparently dry in this experiment; and it seemed

probable that the inflammable matter arose from its decomposition.

The residual potash was unaltered; it contained indeed a number of

dark grey metallic particles, but these proved to be derived from the

platina.

I tried several experiments on the electrization of potash rendered

fluid by heat, with the hopes of being able to collect the combustible

matter, but without success; and I only attained my object by employing

electricity as the common agent for fusion and decomposition.

Though potash, perfectly dried by ignition, is a non-conductor, yet it

is rendered a conductor by a very slight addition of moisture, which

does not perceptibly destroy its aggregation; and in this state it

readily fuses and decomposes by strong electrical powers.

A small piece of pure potash, which had been exposed for a few seconds

to the atmosphere, so as to give conducting power to the surface, was

placed upon an insulated disc of platina, connected with the negative

side of the battery of the power of 250 of 6 and 4, in a state of

intense activity; and a platina wire, communicating with the positive

side, was brought in contact with the upper surface of the alkali. The

whole apparatus was in the open atmosphere.

Under these circumstances a vivid action was soon observed to take

place. The potash began to fuse at both its points of electrization.

There was a violent effervescence at the upper surface; at the lower,

or negative surface, there was no liberation of elastic fluid; but

small globules having a high metallic lustre, and being precisely

similar in visible characters to quicksilver, appeared, some of which

burnt with explosion and bright flame, as soon as they were formed, and

others remained, and were merely tarnished, and finally covered by a

white film which formed on their surfaces.

These globules, numerous experiments soon showed to be the substance

I was in search of, and a peculiar inflammable principle the basis

of potash. I found that the platina was in no way connected with the

result, except as the medium for exhibiting the electrical powers of

decomposition; and a substance of the same kind was produced when

pieces of copper, silver, gold, plumbago, or even charcoal were

employed for completing the circuit.

The phenomenon was independent of the presence of air; I found that it

took place when the alkali was in the vacuum of an exhausted receiver.

The substance was likewise produced from potash fused by means of

a lamp, in glass tubes confined by mercury, and furnished with

hermetically inserted platina wires by which the electrical action

was transmitted. But this operation could not be carried on for any

considerable time; the glass was rapidly dissolved by the action of

the alkali, and this substance soon penetrated through the body of the

tube.

Soda, when acted upon in the same manner as potash, exhibited an

analogous result; but the decomposition demanded greater intensity

of action in the batteries, or the alkali was required to be in much

thinner and smaller pieces. With the battery of 100 of 6 inches in full

activity I obtained good results from pieces of potash weighing from

40 to 70 grains, and of a thickness which made the distance of the

electrified metallic surfaces nearly a quarter of an inch; but with a

similar power it was impossible to produce the effects of decomposition

on pieces of soda of more than 15 or 20 grains in weight, and that only

when the distance between the wires was about 1/8 or 1/10 of an inch.

The substance produced from potash remained fluid at the temperature of

the atmosphere at the time of its production; that from soda, which was

fluid in the degree of heat of the alkali during its formation, became

solid on cooling, and appeared having the lustre of silver.

When the power of 250 was used, with a very high charge for the

decomposition of soda, the globules often burnt at the moment of their

formation, and sometimes violently exploded and separated into smaller

globules, which flew with great velocity through the air in a state of

vivid combustion, producing a beautiful effect of continued jets of

fire.

THEORY OF THE DECOMPOSITION OF THE FIXED ALKALIES; THEIR COMPOSITION

AND PRODUCTION

As in all decompositions of compound substances which I had previously

examined, at the same time that combustible bases were developed at

the negative surface in the electrical circuit, oxygen was produced,

and evolved or carried into combination at the positive surface, it

was reasonable to conclude that this substance was generated in a

similar manner by the electrical action upon the alkalies; and a number

of experiments made above mercury, with the apparatus for excluding

external air, proved that this was the case.

When solid potash, or soda in its conducting state, was included

in glass tubes furnished with electrified platina wires, the new

substances were generated at the negative surfaces; the gas given out

at the other surface proved by the most delicate examination to be pure

oxygen; and unless an excess of water was present, no gas was evolved

from the negative surface.

In the synthetical experiments, a perfect coincidence likewise will be

found.

I mentioned that the metallic lustre of the substance from potash

immediately became destroyed in the atmosphere, and that a white crust

formed upon it. This crust I soon found to be pure potash, which

immediately deliquesced, and new quantities were formed, which in their

turn attracted moisture from the atmosphere till the whole globule

disappeared, and assumed the form of a saturated solution of potash.

When globules were placed in appropriate tubes containing common air

or oxygen gas confined by mercury, an absorption of oxygen took place;

a crust of alkali instantly formed upon the globule; but from the want

of moisture for its solution, the process stopped, the interior being

defended from the action of the gas.

With the substance from soda, the appearances and effects were

analogous.

When the substances were strongly heated, confined in given proportions

of oxygen, a rapid combustion with a brilliant white flame was

produced, and the metallic globules were found converted into a white

and solid mass, which in the case of the substance from potash was

found to be potash, and in the case of that from soda, soda.

Oxygen gas was absorbed in this operation, and nothing emitted which

affected the purity of the residual air.

The alkalies produced were apparently dry, or at least contained no

more moisture than might well be conceived to exist in the oxygen

gas absorbed; and their weights considerably exceeded those of the

combustible matters consumed.

The processes on which these conclusions are founded will be fully

described hereafter, when the minute details which are necessary will

be explained, and the proportions of oxygen, and of the respective

inflammable substances which enter into union to form the fixed

alkalies, will be given.

It appears, then, that in these facts there is the same evidence

for the decomposition of potash and soda into oxygen and two

peculiar substances, as there is for the decomposition of sulphuric

and phosphoric acids and the metallic oxides into oxygen and their

respective combustible bases.

In the analytical experiments, no substances capable of decomposition

are present but the alkalies and a minute portion of moisture; which

seems in no other way essential to the result, than in rendering them

conductors at the surface: for the new substances are not generated

till the interior, which is dry, begins to be fused; they explode when

in rising through the fused alkali they come in contact with the heated

moistened surface; they cannot be produced from crystallised alkalies,

which contain much water; and the effect produced by the electrization

of ignited potash, which contains no sensible quantity of water,

confirms the opinion of their formation independently of the presence

of this substance.

The combustible bases of the fixed alkalies seem to be repelled as

other combustible substances, by positively electrified surfaces, and

attracted by negatively electrified surfaces, and the oxygen follows

the contrary order; or the oxygen being naturally possessed of the

negative energy, and the bases of the positive, do not remain in

combination when either of them is brought into an electrical state

opposite to its natural one. In the synthesis, on the contrary, the

natural energies or attractions come in equilibrium with each other;

and when these are in a low state at common temperatures, a slow

combination is effected; but when they are exalted by heat, a rapid

motion is the result; and as in other like cases with the production of

fire.

FOOTNOTES:

[Footnote 28: From the _Transactions of the Royal Society of

London_.]

XXVI

MICHAEL FARADAY

1791-1867

_Born on September 22, 1791, at Newington, Surrey, England,

Michael Faraday was the son of a blacksmith. After an early and very

elementary education, he was apprenticed in 1805 to a book-binder in

whose service he read widely and thus educated himself. Developing an

interest in physics, he attended the evening lectures of Sir Humphrey

Davy who, in 1813, engaged him as an assistant. Seven years later he

wrote a history of electro-magnetism and succeeded, in the same year,

in getting a needle to rotate fully around a live wire. In 1823 he

liquefied chlorine, an experiment which destroyed the old notion of the

permanent distinction between gases and liquids. In 1831 he discovered

magneto-electric induction and advanced the conception of “lines of

magnetic force.” In 1845, in trying to send polarized rays of light

through heavy magnetized glass, he found that the magnet’s action

interrupted the passage of the light and that magnetization caused the

plane of polarization to rotate. He died August 25, 1867._

ON FLUID CHLORINE[29]

_Read March 13, 1823._

It is well known that before the year 1810, the solid substance

obtained by exposing chlorine, as usually procured, to a low

temperature, was considered as the gas itself reduced into that form;

and that Sir Humphrey Davy first showed it to be a hydrate, the pure

dry gas not being considerable even at a temperature of 40° F.

I took advantage of the late cold weather to procure crystals of this

substance for the purpose of analysis. The results are contained

in a short paper in the Quarterly Journal of Science, Vol. XV. Its

composition is very nearly 27.7 chlorine, 72.3 water, or 1 proportional

of chlorine, and 10 of water.

The President of the Royal Society having honoured me by looking at

these conclusions, suggested, that an exposure of the substance to

heat under pressure, would probably lead to interesting results; the

following experiments were commenced at his request. Some hydrate

of chlorine was prepared, and being dried as well as could be by

pressure in bibulous paper, was introduced into a sealed glass tube,

the upper end of which was then hermetically closed. Being placed

in water at 60°, it underwent no change; but when put into water

at 100°, the substance fused, the tube became filled with a bright

yellow atmosphere, and, on examination, was found to contain two

fluid substances: the one, about three-fourths of the whole, was of

a faint yellow colour, having very much the appearance of water; the

remaining fourth was a heavy bright yellow fluid, lying at the bottom

of the former, without any apparent tendency to mix with it. As the

tube cooled, the yellow atmosphere condensed into more of the yellow

fluid, which floated in a film on the pale fluid, looking very like

chloride of nitrogen; and at 70° the pale portion congealed, although

even at 32° the yellow portion did not solidify. Heated up to 100° the

yellow fluid appeared to boil, and again produced the bright coloured

atmosphere.

By putting the hydrate into a bent tube, afterwards hermetically

sealed, I found it easy, after decomposing it by a heat of 100°, to

distil the yellow fluid to one end of the tube, and so separate it from

the remaining portion. In this way a more complete decomposition of the

hydrate was effected, and, when the whole was allowed to cool, neither

of the fluids solidified at temperatures above 34°, and the yellow

portion not even at 0°. When the two were mixed together they gradually

combined at temperatures below 60°, and formed the same solid substance

as that first introduced. If, when the fluids were separated, the tube

was cut in the middle, the parts flew asunder as if with an explosion,

the whole of the yellow portion disappeared, and there was a powerful

atmosphere of chlorine produced; the pale portion on the contrary

remained, and when examined, proved to be a weak solution of chlorine

in water, with a little muriatic acid, probably from the impurity of

the hydrate used. When that end of the tube in which the yellow fluid

lay was broken under a jar of water, there was an immediate production

of chlorine gas.

I at first thought that muriatic acid and euchlorine had been formed;

then, that two new hydrates of chlorine had been produced; but at

last I suspected that the chlorine had been entirely separated from

the water by the heat and condensed into a dry fluid by the mere

pressure of its own abundant vapour. If that were true, it followed,

that chlorine gas, when compressed, should be condensed into the

same fluid, and, as the atmosphere in the tube in which the fluid

lay was not very yellow at 50° or 60°, it seemed probable that the

pressure required was not beyond what could readily be obtained by a

condensing syringe. A long tube was therefore furnished with a cap and

stop-cock, then exhausted of air and filled with chlorine, and being

held vertically with the syringe upwards, air was forced in, which

thrust the chlorine to the bottom of the tube, and gave a pressure of

about 4 atmospheres. Being now cooled, there was an immediate deposit

in films, which appeared to be hydrate, formed by water contained in

the gas and vessels, but some of the yellow fluid was also produced.

As this however might also contain a portion of the water present,

a perfectly dry tub and apparatus were taken, and the chlorine left

for some time over a bath of sulphuric acid before it was introduced.

Upon throwing in air and giving pressure, there was now no solid film

formed, but the clear yellow fluid was deposited, and more abundantly

still upon cooling. After remaining some time it disappeared, having

gradually mixed with the atmosphere above it, but every repetition of

the experiment produced the same results.

Presuming that I had now a right to consider the yellow fluid as pure

chlorine in the liquid state, I proceeded to examine its properties,

as well as I could when obtained by heat from the hydrate. However

obtained, it always appears very limpid and fluid, and excessively

volatile at common pressure. A portion was cooled in its tube to 0°;

it remained fluid. The tube was then opened, when a part immediately

flew off, leaving the rest so cooled by the evaporation as to remain a

fluid under the atmospheric pressure. The temperature could not have

been higher than 40° in this case; as Sir Humphrey Davy has shown

that dry chlorine does not condense at that temperature under common

pressure. Another tube was opened at a temperature of 50°; a part of

the chlorine volatilised, and cooled the tube so much as to condense

the atmospheric vapour on it as ice.

A tube having the water at one end and the chlorine at the other was

weighed, and then cut in two; the chlorine immediately flew off, and

the loss being ascertained was found to be 1.6 grains: the water

left was examined and found to contain some chlorine: its weight was

ascertained to be 5.4 grains. These proportions, however, must not

be considered as indicative of the true composition of hydrate of

chlorine; for, from the mildness of the weather during the time when

these experiments were made, it was impossible to collect the crystals

of hydrate, press, and transfer them, without losing much chlorine; and

it is also impossible to separate the chlorine and water in the tube

perfectly, or keep them separate, as the atmosphere within will combine

with the water, and gradually reform the hydrate.

Before cutting the tube, another tube had been prepared exactly like it

in form and size, and a portion of water introduced into it, as near as

the eye could judge, of the same bulk as the fluid chlorine: this water

was found to weigh 1.2 grains; a result, which, if it may be trusted,

would give the specific gravity of fluid chlorine as 1.33; and from its

appearance in, and on water, this cannot be far wrong.

ELECTRICITY FROM MAGNETISM

_Read November 24, 1831._

1. The power which electricity of tension possesses of causing an

opposite electrical state in its vicinity has been expressed by the

general term Induction; which, as it has been received into scientific

language, may also, with propriety, be used in the same general sense

to express the power which electrical currents may possess of inducing

any particular state upon matter in their immediate neighborhood,

otherwise indifferent. It is with this meaning that I purpose using it

in the present paper.

2. Certain effects of the induction of electrical currents have already

been recognized and described: as those of magnetization; Ampère’s

experiments of bringing a copper disc near to a flat spiral; his

repetition with electro-magnets of Arago’s extraordinary experiments,

and perhaps a few others. Still it appeared unlikely that these

could be all the effects which induction by currents could produce;

especially as, upon dispensing with iron, almost the whole of them

disappear, whilst yet an infinity of bodies, exhibiting definite

phenomena of induction with electricity of tension still remain to be

acted upon by the induction of electricity in motion.

3. Further: whether Ampère’s beautiful theory were adopted, or any

other, or whatever reservation were mentally made, still it appeared

very extraordinary, that, as every electric current was accompanied by

a corresponding intensity of magnetic action at right angles to the

current, good conductors of electricity, when placed within the sphere

of this action, should not have any current induced through them, or

some sensible effect produced equivalent in force to such a current.

4. These considerations, with their consequence, the hope of obtaining

electricity from ordinary magnetism, have stimulated me at various

times to investigate experimentally the inductive effect of electric

currents. I lately arrived at positive results; and not only had my

hopes fulfilled, but obtained a key which appeared to me to open out a

full explanation of Arago’s magnetic phenomena, and also to discover a

new state, which may probably have great influence in some of the most

important effects of electric currents.

5. These results I purpose describing, not as they were obtained, but

in such a manner as to give the most concise view of the whole.

EVOLUTION OF ELECTRICITY FROM MAGNETISM

27. A welded ring was made of soft round bar-iron, the metal being

seven-eighths of an inch in thickness, and the ring six inches in

external diameter. Three helices were put round one part of this ring,

each containing about twenty-four feet of copper wire one-twentieth

of an inch thick; they were insulated from the iron and each other,

and superposed in the manner before described (6), occupying about

nine inches in length upon the ring. They could be used separately or

conjointly; the group may be distinguished by the letter A. On the

other part of the ring about sixty feet of similar copper wire in two

pieces were applied in the same manner, forming a helix B, which had

the same common direction with the helices of A, but being separated

from it at each extremity by about half an inch of the uncovered iron.

28. The helix B, was connected by copper wires with a galvanometer

three feet from the ring. The helices of A were connected end to

end so as to form one common helix, the extremities of which were

connected with a battery of ten pairs of plates four inches square. The

galvanometer was immediately affected, and to a degree far beyond what

has been described when with a battery of tenfold power helices without

iron were used (10); but though the contact was continued, the effect

was not permanent, for the needle soon came to rest in its natural

position, as if quite indifferent to the attached electro-magnetic

arrangement. Upon breaking the contact with the battery, the needle

was again powerfully deflected, but in the contrary direction to that

induced in the first instance.

29. Upon arranging the apparatus so that B should be out of use, the

galvanometer be connected with one of the three wires of A (27), and

the other two made into a helix through which the current from the

trough (28) was passed, similar but rather more powerful effects were

produced.

30. When the battery contact was made in one direction, the

galvanometer-needle was deflected on the one side; if made in the other

direction, the deflection was on the other side. The deflection on

breaking the battery contact was always the reverse of that produced

by completing it. The deflection on making a battery contact always

indicated an induced current in the opposite direction to that from

the battery; but on breaking the contact the deflection indicated

an induced current in the same direction as that of the battery.

No making or breaking of the contact at B side, or in any part of

the galvanometer circuit, produced any effect at the galvanometer.

No continuance of the battery current caused any deflection of the

galvanometer-needle. As the above results are common to all these

experiments, and to similar ones with ordinary magnets to be hereafter

detailed, they need not be again particularly described.

31. Upon using the power of 100 pairs of plates (10) with this ring,

the impulse at the galvanometer, when contact was completed or broken,

was so great as to make the needle spin round rapidly four or five

times, before the air and terrestrial magnetism could reduce its motion

to mere oscillation.

39. But as might be supposed that in all the preceding experiments of

this section, it was by some peculiar effect taking place during the

formation of the magnet, and not by its mere virtual approximation,

that the momentary induced current was excited, the following

experiment was made. All the similar ends of the compound hollow

helix (34) were bound together by copper wire, forming two general

terminations, and these were connected with the galvanometer. The soft

iron cylinder (34) was removed, and a cylindrical magnet three-quarters

of an inch in diameter and eight inches and a half in length, used

instead. One end of this magnet was introduced into the axis of the

helix and then, the galvanometer-needle being stationary, the magnet

was suddenly thrust in; immediately the needle was deflected in the

same direction as if the magnet had been formed by either of the two

preceding processes (34, 36). Being left in, the needle resumed its

first position, and then the magnet being withdrawn the needle was

deflected in the opposite direction. These effects were not great; but

by introducing and withdrawing the magnet, so that the impulse each

time should be added to those previously communicated to the needle,

the latter could be made to vibrate through an arc of 180° or more.

40. In this experiment the magnet must not be passed entirely through

the helix, for then a second action occurs. When the magnet is

introduced the needle at the galvanometer is deflected in a certain

direction; but being in, whether it be pushed quite through or

withdrawn, the needle is deflected in a direction the reverse of that

previously produced. When the magnet is passed in and through at one

continuous motion, the needle moves one way, is then suddenly stopped,

and finally moves the other way.

41. If such a hollow helix as that described (34) be laid east and west

(or in any other constant position), and a magnet be retained east and

west, its marked pole always being one way; then whichever end of the

helix the magnet goes in at, and consequently whichever pole of the

magnet enters first, still the needle is deflected the same way: on the

other hand, whichever direction is followed in withdrawing the magnet,

the deflection is constant, but contrary to that due to its entrance.

57. The various experiments of this section prove, I think, most

completely the production of electricity from ordinary magnetism.

That its intensity should be very feeble and quantity small,

cannot be considered wonderful, when it is remembered that like

thermo-electricity it is evolved entirely within the substance of

metals retaining all their conducting power. But an agent which is

conducted along the metallic wires in the manner described; which,

whilst so passing possesses the peculiar magnetic actions and force

of a current of electricity; which can agitate and convulse the limbs

of a frog; and which, finally, can produce a spark by its discharge

through charcoal (32), can only be electricity. As all the effects can

be produced by ferruginous electro-magnets (34), there is no doubt that

arrangements like the magnets of Professors Moll, Henry, Ten Eyke, and

others, in which as many as two thousand pounds have been lifted, may

be used for these experiments; in which case not only a brighter spark

may be obtained, but wires also ignited, and, as the current can pass

liquids (23), chemical action be produced. These effects are still

more likely to be obtained when the magneto-electric arrangements to

be explained in the fourth section are excited by the powers of such

apparatus.

58. The similarity of action, almost amounting to identity, between

common magnets and either electro-magnets or volta-electric currents,

is strikingly in accordance with and confirmatory of M. Ampère’s

theory, and furnishes powerful reasons for believing that the action

is the same in both cases; but, as a distinction in language is still

necessary, I propose to call the agency thus exerted by ordinary

magnets, magneto-electric or magnelectric induction (26).

59. The only difference which powerfully strikes the attention as

existing between volta-electric and magneto-electric induction, is the

suddenness of the former, and the sensible time required by the latter:

but even in this early state of investigation there are circumstances

which seem to indicate, that upon further inquiry this difference will,

as a philosophical distinction, disappear (68).

FOOTNOTES:

[Footnote 29: This excerpt and the one following are from the

_Transactions of the Royal Society of London_.]

XXVII

JOSEPH HENRY

1797-1878

_Born at Albany, New York, December 17, 1797, Joseph Henry prepared

for the profession of medicine, but an appointment as an assistant

engineer on the state road diverted his interests toward mechanics.

In 1826 he was appointed instructor of physics at Albany Institute,

now the Albany Boys Academy, where he conducted his first experiments

in electricity. In 1828 he first produced a strong electro-magnet by

winding fine insulated wire around a piece of soft iron, and soon

succeeded in exciting his electro-magnet at a distance by the use of

high intensity batteries made up of many cells. Demonstrating that

the number of coils of fine wire about a magnet had as much influence

as the intensity of the current and that after winding many coils

around the soft iron magnet it could still be made magnetic, he

suggested the principle which Morse later used in the telegraph. In

1832 he discovered that in a long conductor the primary current, by an

induction upon itself, produced a number of secondary currents that

greatly increased the intensity of the discharge._

_He was appointed professor of natural philosophy at Princeton

University in 1832 and became secretary of the Smithsonian Institution

in 1846. He died in Washington, May 13, 1878._

ON THE PRODUCTION OF CURRENTS AND SPARKS OF ELECTRICITY FROM

MAGNETISM[30]

Although the discoveries of Oersted, Arago, Faraday, and others, have

placed the intimate connection of electricity and magnetism in a most

striking point of view, and although the theory of Ampère has referred

all the phenomena of both these departments of science to the same

general laws, yet until lately one thing remained to be proved by

experiment, in order more fully to establish their identity; namely,

the possibility of producing electrical effects from magnetism.

It is well known that surprising magnetic results can readily be

obtained from electricity, and at first sight it might be supposed

that electrical effects could with equal facility be produced from

magnetism; but such has not been found to be the case, for although the

experiment has often been attempted, it has nearly as often failed.

It early occurred to me that if galvanic magnets on my plan were

substituted for ordinary magnets, in researches of this kind, more

success might be expected. Besides their great powers these magnets

possess other properties, which render them important instruments in

the hands of the experimenter; their polarity can be instantaneously

reversed, and their magnetism suddenly destroyed or called into full

action, according as the occasion may require. With this view, I

commenced, last August, the construction of a much larger galvanic

magnet than, to my knowledge, had before been attempted, and also made

preparations for a series of experiments with it on a large scale,

in reference to the production of electricity from magnetism. I was,

however, at that time accidentally interrupted in the prosecution of

these experiments, and have not been able since to resume them until

within the last few weeks, and then on a much smaller scale than was

at first intended. In the meantime, it has been announced in the 117th

number of the _Library of Useful Knowledge_, that the result

so much sought after has at length been found by Mr. Faraday of the

Royal Institution. It states that he has established the general fact,

that when a piece of metal is moved in any direction, in front of a

magnetic pole, electrical currents are developed in the metal, which

pass in a direction at right angles to its own motion, and also that

the application of this principle affords a complete and satisfactory

explanation of the phenomena of magnetic rotation. No detail is given

of the experiments, and it is somewhat surprising that results so

interesting, and which certainly form a new era in the history of

electricity and magnetism, should not have been more fully described

before this time in some of the English publications; the only mention

I have found of them is the following short account from the _Annals

of Philosophy_ for April, under the head of Proceedings of the Royal

Institution:

“Feb. 17.--Mr. Faraday gave an account of the first two parts of

his researches in electricity; namely, Volta-electric induction and

magneto-electric induction. If two wires, A and B, be placed side by

side, but not in contact, and a Voltaic current be passed through

A, there is instantly a current produced by induction in B, in the

opposite direction. Although the principal current in A be continued,

still the secondary current in B is not found to accompany it, for

it ceases after the first moment, but when the principal current is

stopped, then there is a second current produced in B, in the opposite

direction to that of the first produced by the inductive action, or in

the same direction as that of the principal current.

“If a wire, connected at both extremities with a galvanometer,

be coiled in the form of a helix around a magnet, no current of

electricity takes place in it. This is an experiment which has been

made by various persons hundreds of times, in the hope of evolving

electricity from magnetism, and in other cases in which the wishes of

the experimenter and the facts are opposed to each other, has given

rise to very conflicting conclusions. But if the magnet be withdrawn

from or introduced into such a helix, a current of electricity is

produced whilst the magnet is in motion, and is rendered evident by

the deflection of the galvanometer. If a single wire be passed by a

magnetic pole, a current of electricity is induced through it which

can be rendered sensible.”

Before having any knowledge of the method given in the above account, I

had succeeded in producing electrical effects in the following manner,

which differs from that employed by Mr. Faraday, and which appears to

me to develop some new and interesting facts. A piece of copper wire,

about thirty feet long and covered with elastic varnish, was closely

coiled around the middle of the soft iron armature of the galvanic

magnet described in Vol. XIX of the _American Journal of Science_,

and which, when excited, will readily sustain between six hundred and

seven hundred pounds. The wire was wound upon itself so as to occupy

only about one inch of the length of the armature which is seven inches

in all. The armature, thus furnished with the wire, was placed in its

proper position across the ends of the galvanic magnet, and there

fastened so that no motion could take place. The two protecting ends

of the helix were dipped into two cups of mercury, and there connected

with a distant galvanometer by means of two copper wires, each about

forty feet long. This arrangement being completed, I stationed myself

near the galvanometer and directed an assistant at a given word to

immerse suddenly, in a vessel of dilute acid, the galvanic battery

attached to the magnet. At the instant of immersion, the north end

of the needle was deflected 30° to the west, indicating a current

of electricity from the helix surrounding the armature. The effect,

however, appeared only as a single impulse, for the needle, after a few

oscillations, resumed its former undisturbed position in the magnetic

meridian, although the galvanic action of the battery, and consequently

the magnetic power, was still continued. I was, however, much surprised

to see the needle suddenly deflected from a state of rest to about 20°

to the east, or in a contrary direction when the battery was withdrawn

from the acid, and again deflected to the west when it was re-immersed.

This operation was repeated many times in succession, and uniformly

with the same result, the armature the whole time remaining immovably

attached to the poles of the magnet, no motion being required to

produce the effect, as it appeared to take place only in consequence of

the instantaneous development of the magnetic action in one, and the

sudden cessation of it in the other.

This experiment illustrates most strikingly the reciprocal action of

the two principles of electricity and magnetism, if indeed it does not

establish their absolute identity. In the first place, magnetism is

developed in the soft iron of the galvanic magnet by the action of the

currents of electricity from the battery, and secondly, the armature,

rendered magnetic by contact with the poles of the magnet, induces in

its turn currents of electricity in the helix which surrounds it; we

have thus, as it were, electricity converted into magnetism and this

magnetism again into electricity.

Another fact was observed which is somewhat interesting, inasmuch as it

serves in some respects to generalize the phenomena. After the battery

had been withdrawn from the acid, and the needle of the galvanometer

suffered to come to a state of rest after the resulting deflection, it

was again deflected in the same direction by partially detaching the

armature from the poles of the magnet to which it continued to adhere

from the action of the residual magnetism, and in this way, a series of

deflections, all in the same direction, was produced by merely slipping

off the armature by degrees until the contact was entirely broken. The

following extract from the register of the experiments exhibits the

relative deflections observed in one experiment of this kind.

At the instant of immersion of the battery, deflection 40° west.

At the instant of emersion of the battery, deflection 18° east.

Armature partially detached, deflection 7° east.

Armature entirely detached, deflection 12° west.

The effect was reversed in another experiment, in which the needle was

turned to the west in a series of deflections by dipping the battery

but a small distance into the acid at first and afterwards immersing it

by degrees.

From the foregoing facts it appears that a current of electricity is

produced, for an instant, in a helix of copper wire surrounding a piece

of soft iron whenever magnetism is induced in the iron; and a current

in an opposite direction when the magnetic action ceases; also that an

instantaneous current in one or the other direction accompanies every

change in the magnetic intensity of the iron.

Since reading the account before given of Mr. Faraday’s method of

producing electrical currents I have attempted to combine the effects

of motion and induction; for this purpose a rod of soft iron ten inches

long and one inch and a quarter in diameter, was attached to a common

turning lathe, and surrounded with four helices of copper wire in such

a manner that it could be suddenly and powerfully magnetized, while

in rapid motion, by transmitting galvanic currents through three of

the helices; the fourth being connected with the distant galvanometer

was intended to transmit the current of induced electricity; all the

helices were stationary while the iron rod revolved on its axis within

them. From a number of trials in succession, first with the rod in one

direction, then in the opposite, and next in a state of rest, it was

concluded that no perceptible effect was produced on the intensity of

the magneto-electric current by a rotary motion of the iron combined

with its sudden magnetization.

The same apparatus, however, furnished the means of measuring

separately the relative power of motion and induction in producing

electrical currents. The iron rod was first magnetized by currents

through the helices attached to the battery and while in this state

one of its ends was quickly introduced into the helix connected with

the galvanometer; the deflection of the needle in this case was

seven degrees. The end of the rod was next introduced into the same

helix while in its natural state and then suddenly magnetized; the

deflection in this instance amounted to thirty degrees, showing a great

superiority in the method of induction.

The next attempt was to increase the magneto-electric effect while the

magnetic power remained the same, and in this I was more successful.

Two iron rods six inches long and one inch in diameter were each

surrounded by two helices and then placed perpendicularly on the

face of the armature, and between it and the poles of the magnet,

so that each rod formed, as it were, a prolongation of the poles,

and to these the armature adhered when the magnet was excited. With

this arrangement, a current from one helix produced a deflection of

thirty-seven degrees; from two helices both on the same rod, fifty-two

degrees, and from three fifty-nine degrees; but when four helices

were used, the deflection was only fifty-five degrees, and when to

these were added the helix of smaller wire around the armature, the

deflection was no more than thirty degrees. This result may perhaps

have been somewhat affected by the want of proper insulation in the

several spires of the helices; it, however, establishes the fact that

an increase in the electric current is produced by using at least

two or three helices instead of one. The same principle was applied

to another arrangement which seems to afford the maximum of electric

development from a given magnetic power; in place of the two pieces of

iron and the armature used in the last experiments, the poles of the

magnet were connected by a single rod of iron, bent into the form of a

horse-shoe, and its extremities filed perfectly flat so as to come in

perfect contact with the faces of the poles; around the middle of the

arch of this horse-shoe, two strands of copper wire were tightly coiled

one over the other. A current from one of these helices deflected the

needle one hundred degrees, and when both were used the needle was

deflected with such force as to make a complete circuit. But the most

surprising effect was produced when, instead of passing the current

through the long wires to the galvanometer, the opposite ends of the

helices were held nearly in contact with each other, and the magnet

suddenly excited; in this case a small but vivid spark was seen to pass

between the ends of the wires, and this effect was repeated as often as

the state of intensity of the magnet was changed.

In these experiments the connection of the battery with the wires from

the magnet was not formed by soldering, but by two cups of mercury,

which permitted the galvanic action on the magnet to be instantaneously

suspended and the polarity to be changed and rechanged without removing

the battery from the acid; a succession of vivid sparks was obtained

by rapidly interrupting and forming the communication by means of one

of these cups; but the greatest effect was produced when the magnetism

was entirely destroyed and instantaneously reproduced by a change of

polarity.

It appears from the May number of the _Annals of Philosophy_ that

I have been anticipated in this experiment of drawing sparks from the

magnet by Mr. James D. Forbes of Edinburgh, who obtained a spark on the

30th of March; my experiment being made during the last two weeks of

June. A simple notification of his result is given, without any account

of the experiment, which is reserved for a communication to the Royal

Society of Edinburgh; my result is therefore entirely independent of

his and was undoubtedly obtained by a different process.

ELECTRICAL SELF-INDUCTION IN A LONG HELICAL WIRE

I have made several other experiments in relation to the same subject,

but which more important duties will not permit me to verify in time

for this paper. I may, however, mention one fact which I have not seen

noticed in any work, and which appears to me to belong to the same

class of phenomena as those before described; it is this: when a small

battery is moderately excited by diluted acid, and its poles, which

should be terminated by cups of mercury, are connected by a copper

wire not more than a foot in length, no spark is perceived when the

connection is either formed or broken; but if a wire thirty or forty

feet long be used instead of the short wire, though no spark will be

perceptible when the connection is made, yet when it is broken by

drawing one end of the wire from its cup of mercury, a vivid spark

is produced. If the action of the battery be very intense, a spark

will be given by the short wire; in this case it is only necessary to

wait a few minutes until the action partially subsides, and until no

more sparks are given from the short wire; if the long wire be now

substituted a spark will again be obtained. The effect appears somewhat

increased by coiling the wire into a helix; it seems also to depend in

some measure on the length and thickness of the wire. I can account for

these phenomena only by supposing the long wire to become charged with

electricity, which by its reaction on itself projects a spark when the

connection is broken.

FOOTNOTES:

[Footnote 30: Silliman’s _American Journal of Science_, July,

1832, Vol. XXII, pp. 403-408; _Scientific Writings_, Vol. I., p.

73.]

XXVIII

SIR CHARLES LYELL

1797-1875

_Sir Charles Lyell, the son of a Scottish botanist of literary

tastes, was born at Kinnordy, Scotland, November 14, 1797. He went to

Oxford University, from which he graduated in 1819. He was admitted to

the bar in 1825. In 1827 he abandoned law for geology, and published

his “Principles of Geology” in 1830-1833. Lyell’s thesis was that

all the past changes of the earth were explainable by forces now

operative--an idea which underlies modern geology. He published his

“Antiquity of Man” in 1863, providing proofs of man’s long existence

on earth and thus contributing to the establishment of the Darwinian

theory. He died February 22, 1875._

UNIFORMITY IN THE SERIES OF PAST CHANGES IN THE ANIMATE AND INANIMATE

WORLD[31]

_Origin of the doctrine of alternate periods of repose and

disorder._--It has been truly observed that when we arrange the

fossiliferous formations in chronological order, they constitute

a broken and defective series of monuments; we pass without any

intermediate gradations from systems of strata which are horizontal, to

other systems which are highly inclined--from rocks of peculiar mineral

composition to others which have a character wholly distinct--from one

assemblage of organic remains to another, in which frequently nearly

all the species, and a large part of the genera, are different. These

violations of continuity are so common as to constitute in most regions

the rule rather than the exception, and they have been considered by

many geologists as conclusive in favour of sudden revolutions in the

inanimate and animate world. We have already seen that according to

the speculations of some writers, there have been in the past history

of the planet alternate periods of tranquility and convulsion, the

former enduring for ages, and resembling the state of things now

experienced by man; the other brief, transient, and paroxysmal, giving

rise to new mountains, seas, and valleys, annihilating one set of

organic beings and ushering in the creation of another.

It will be the object of the present chapter to demonstrate that

these theoretical views are not borne out by a fair interpretation of

geological monuments. It is true that in the solid framework of the

globe we have a chronological chain of natural records, many links of

which are wanting: but a careful consideration of all the phenomena

leads to the opinion that the series was originally defective--that

it has been rendered still more so by time--that a great part of what

remains is inaccessible to man, and even of that fraction which is

accessible nine-tenths or more are to this day unexplored.

The readiest way, perhaps, of persuading the reader that we may

dispense with great and sudden revolutions in the geological order

of events is by showing him how a regular and uninterrupted series

of changes in the animate and inanimate world must give rise to such

breaks in the sequence, and such unconformability of stratified rocks,

as are usually thought to imply convulsions and catastrophes. It is

scarcely necessary to state that the order of events thus assumed to

occur, for the sake of illustration, should be in harmony with all

the conclusions legitimately drawn by geologists from the structure

of the earth, and must be equally in accordance with the changes

observed by man to be now going on in the living as well as in the

inorganic creation. It may be necessary in the present state of science

to supply some part of the assumed course of nature hypothetically;

but if so, this must be done without any violation of probability,

and always consistently with the analogy of what is known both of the

past and present economy of our system. Although the discussion of so

comprehensive a subject must carry the beginner far beyond his depth,

it will also, it is hoped, stimulate his curiosity, and prepare him to

read some elementary treatises on geology with advantage, and teach

him the bearing on that science of the changes now in progress on the

earth. At the same time it may enable him the better to understand the

intimate connection between the Second and Third Books of this work,

one of which is occupied with the changes of the inorganic, the latter

with those of the organic creation.

In pursuance, then, of the plan above proposed, I will consider

in this chapter, first, the laws which regulate the denudation of

strata and the deposition of sediment; secondly, those which govern

the fluctuation in the animate world; and thirdly, the mode in which

subterranean movements affect the earth’s crust.

_Uniformity of change considered, first, in reference to denudation

and sedimentary deposition._--First, in regard to the laws governing

the deposition of new strata. If we survey the surface of the globe,

we immediately perceive that it is divisible into areas of deposition

and non-deposition; or, in other words, at any given time there are

spaces which are the recipients, others which are not the recipients,

of sedimentary matter. No new strata, for example, are thrown down on

dry land, which remains the same from year to year; whereas, in many

parts of the bottom of seas and lakes, mud, sand, and pebbles are

annually spread out by rivers and currents. There are also great masses

of limestone growing in some seas, chiefly composed of corals and

shells, or, as in the depths of the Atlantic, of chalky mud made up of

foraminifera and diatomaceæ.

As to the dry land, so far from being the receptacle of fresh

accessions of matter, it is exposed almost everywhere to waste away.

Forests may be as dense and lofty as those of Brazil, and may swarm

with quadrupeds, birds, and insects, yet at the end of thousands of

years one layer of black mould a few inches thick may be the sole

representative of those myriads of trees, leaves, flowers, and fruits,

those innumerable bones and skeletons of birds, quadrupeds, and

reptiles, which tenanted the fertile region. Should this land be at

length submerged, the waves of the sea may wash away in a few hours

the scanty covering of mould, and it may merely import a darker shade

of colour to the next stratum of marl, sand, or other matter newly

thrown down. So also at the bottom of the ocean where no sediment is

accumulating, seaweed, zoophytes, fish, and even shells, may multiply

for ages and decompose, leaving no vestige of their form or substance

behind. Their decay, in water, although more slow, is as certain and

eventually as complete as in the open air. Nor can they be perpetuated

for indefinite periods in a fossil state, unless imbedded in some

matrix which is impervious to water, or which at least does not allow

a free percolation of that fluid, impregnated as it usually is, with

a slight quantity of carbonic or other acid. Such a free percolation

may be prevented either by the mineral nature of the matrix itself,

or by the superposition of an impermeable stratum; but if unimpeded,

the fossil shell or bone will be dissolved and removed, particle after

particle, and thus entirely effaced, unless petrification or the

substitution of some mineral for the organic matter happen to take

place.

That there has been land as well as sea at all former geological

periods, we know from the fact that fossil trees and terrestrial plants

are imbedded in rocks of every age, except those which are so ancient

as to be very imperfectly known to us. Occasionally lacrustine and

fluviatile shells, or the bones of amphibious or land reptiles, point

to the same conclusion. The existence of dry land at all periods of the

past implies, as before mentioned, the partial deposition of sediment,

or its limitation to certain areas; and the next point to which I shall

call the reader’s attention is the shifting of these areas from one

region to another.

First, then, variations in the site of sedimentary deposition are

brought about independently of subterranean movements. There is always

a slight change from year to year, or from century to century. The

sediment of the Rhone, for example, thrown in the Lake of Geneva, is

now conveyed to a spot a mile and a half distant from that where it

accumulated in the tenth century, and six miles from the point where

the delta began originally to form. We may look forward to the period

when this lake will be filled up, and then the distribution of the

transported matter will be suddenly altered, for the mud and sand

brought down from the Alps will thenceforth, instead of being deposited

near Geneva, be carried nearly 200 miles southwards, where the Rhone

enters the Mediterranean.

In the deltas of large rivers, such as those of the Ganges and Indus,

the mud is first carried down for many centuries through one arm,

and on this being stopped up it is discharged by another, and may

then enter the sea at a point 50 or 100 miles distant from its first

receptacle. The direction of marine currents is also liable to be

changed by various accidents, as by the heaping up of new sandbanks, or

the wearing away of cliffs and promontories.

But, secondly, all these causes of fluctuation in the sedimentary areas

are entirely subordinate to those great upward or downward movements

of lands, which will be presently spoken of, as prevailing over large

tracts of the globe. By such elevation or subsidence certain spaces

are gradually submerged, or made gradually to emerge: in the one case

sedimentary deposition may be suddenly renewed after having been

suspended for one or more geological periods, in the other as suddenly

made to cease after having continued for ages.

If deposition be renewed after a long interval, the new strata will

usually differ greatly from the sedimentary rocks previously formed

in the same place, and especially if the older rocks have suffered

derangement, which implies a change in the physical geography of the

district since the previous conveyance of sediment to the same spot. It

may happen, however, that, even where the two groups, the superior and

the inferior, are horizontal and conformable to each other, they may

still differ entirely in mineral character, because, since the origin

of the older formation, the geography of some distant country has

been altered. In that country rocks before concealed may have become

exposed by denudation; volcanoes may have burst out and covered the

surface with scoriæ and lava; or new lakes, intercepting the sediment

previously conveyed from the upper country, may have been formed by

subsidence; and other fluctuations may have occurred, by which the

materials brought down from thence by rivers to the sea have acquired a

distinct mineral character.

It is well known that the stream of the Mississippi is charged with

sediment of a different colour from that of the Arkansas and Red

Rivers, which are tinged with red mud, derived from rocks of porphyry

and red gypseous clays in “the far west.” The waters of the Uruguay,

says Darwin, draining a granitic country, are clear and black, those

of the Parana, red. The mud with which the Indus is loaded, says

Burnes, is of a clayey hue, that of the Chenab, on the other hand, is

reddish, that of the Sutlej is more pale. The same causes which make

these several rivers, sometimes situated at no great distance the one

from the other, to differ greatly in the character of their sediment,

will make the waters draining the same country at different epochs,

especially before and after great revolutions in physical geography,

to be entirely dissimilar. It is scarcely necessary to add that marine

currents will be affected in an analogous manner in consequence of the

formation of new shoals, the emergence of new islands, the subsidence

of others, the gradual waste of neighbouring coasts, the growth of

new deltas, the increase of coral reefs, volcanic eruptions, and other

changes.

_Uniformity of change considered, secondly, in reference to the

living creation._--Secondly, in regard to the vicissitudes of

the living creation, all are agreed that the successive groups of

sedimentary strata found in the earth’s new crust are not only

dissimilar in mineral composition for reasons above alluded to, but are

likewise distinguishable from each other by their organic remains. The

general inference drawn from the study and comparison of the various

groups, arranged in chronological order, is this: that at successive

periods distinct tribes of animals and plants have inhabited the land

and waters, and that the organic types of the newer formations are more

analogous to species now existing than those of more ancient rocks. If

we then turn to the present state of the animate creation, and inquire

whether it has now become fixed and stationary, we discover that, on

the contrary, it is in a state of continual flux--that there are many

causes in action which tend to the extinction of species, and which are

conclusive against the doctrine of their unlimited durability.

There are also causes which give rise to new varieties and races in

plants and animals, and new forms are continually supplanting others

which had endured for ages. But natural history has been successfully

cultivated for so short a period, that a few examples only of local,

and perhaps but one or two of absolute, extirpation of species can as

yet be proved, and these only where the interference of man has been

conspicuous. It will nevertheless appear evident, from the facts and

arguments detailed in the chapters which treat of the geographical

distribution of species in the next volume, that man is not the only

exterminating agent; and that, independently of his intervention, the

annihilation of species is promoted by the multiplication and gradual

diffusion of every animal or plant. It will also appear that every

alteration in the physical geography and climate of the globe cannot

fail to have the same tendency. If we proceed still farther, and

inquire whether new species are substituted from time to time for those

which die out, we find that the successive introduction of new forms

appears to have been a constant part of the economy of the terrestrial

system, and if we have no direct proof of the fact it is because the

changes take place so slowly as not to come within the period of exact

scientific observation. To enable the reader to appreciate the gradual

manner in which a passage may have taken place from an extinct fauna to

that now living, I shall say a few words on the fossils of successive

Tertiary periods. When we trace the series of formations from the more

ancient to the more modern, it is in these Tertiary deposits that we

first meet with assemblages of organic remains having a near analogy to

the fauna of certain parts of the globe in our own time. In the Eocene,

or oldest subdivisions, some few of the testacea belong to existing

species, although almost all of them, and apparently all the associated

vertebrata, are now extinct. These Eocene strata are succeeded by a

great number of more modern deposits, which depart gradually in the

character of their fossils from the Eocene type, and approach more and

more to that of the living creation. In the present state of science,

it is chiefly by the aid of shells, that we are enabled to arrive at

these results, for of all classes the testacea are the most generally

diffused in a fossil state, and may be called the medals principally

employed by nature in recording the chronology of past events. In the

Upper Miocene rocks (No. 5 of the table, p. 135) we begin to find a

considerable number, although still a minority, of recent species,

intermixed with some fossils common to the preceding, or Eocene,

epoch. We then arrive at the Pliocene strata, in which species now

contemporary with man begin to preponderate, and in the newest of

which nine-tenths of the fossils agree with species still inhabiting

the neighbouring sea. It is in the Post-Tertiary strata, where all

the shells agree with species now living, that we have discovered the

first or earliest known remains of man associated with the bones of

quadrupeds, some of which are of extinct species.

In thus passing from the older to the newer members of the Tertiary

system, we meet with many chasms, but none which separate entirely,

by a broad line of demarcation, one state of the organic world from

another. There are no signs of an abrupt termination of one fauna and

flora, and the starting into life of new and wholly distinct forms.

Although we are far from being able to demonstrate geologically an

insensible transition from the Eocene to the Miocene, or even from the

latter to the recent fauna, yet the more we enlarge and perfect our

general survey, the more nearly do we approximate to such a continuous

series, and the more gradually are we conducted from times when many of

the genera and nearly all the species were extinct, to those in which

scarcely a single species flourished, which we do not know to exist

at present. Dr. A. Philippi, indeed, after an elaborate comparison

of the fossil tertiary shells of Sicily with those now living in the

Mediterranean, announced, as the result of his examination, that there

are strata in that island which attest a very gradual passage from a

period when only thirteen in a hundred of the shells were like the

species now living in the sea, to an era when the recent species had

attained a proportion of ninety-five in a hundred. There is, therefore,

evidence, he says, in Sicily of this revolution in the animate world

having been effected “without the intervention of any convulsion

or abrupt changes, certain species having from time died out, and

others having been introduced, until at length the existing fauna was

elaborated.”

In no part of Europe is the absence of all signs of man or his works,

in strata of comparatively modern date, more striking than in Sicily.

In the central parts of that island we observe a lofty table-land and

hills, sometimes rising to the height of 3,000 feet, capped with a

limestone, in which from 70 to 85 per cent of the fossil testacea are

specifically identical with those now inhabiting the Mediterranean.

These calcareous and other argillaceous strata of the same age are

intersected by deep valleys which appear to have been gradually formed

by denudation, but have not varied materially in width or depth since

Sicily was first colonized by the Greeks. The limestone, moreover,

which is of so late a date in geological chronology, was quarried for

building those ancient temples of Girgenti and Syracuse, of which the

ruins carry us back to a remote era in human history. If we are lost

in conjectures when speculating on the ages required to lift up these

formations to the height of several thousand feet above the sea, and

to excavate the valleys, how much more remote must be the era when the

same rocks were gradually formed beneath the waters!

The intense cold of the Glacial period was spoken of in the tenth

chapter. Although we have not yet succeeded in detecting proofs of the

origin of man antecedently to that epoch, we have yet found evidence

that most of the testacea, and not a few of the quadrupeds, which

preceded, were of the same species as those which followed the extreme

cold. To whatever local disturbances this cold may have given rise in

the distribution of species, it seems to have done little in effecting

their annihilation. We may conclude, therefore, from a survey of

the tertiary and modern strata, which constitute a more complete and

unbroken series than rocks of older date, that the extinction and

creation of species have been, and are, the result of a slow and

gradual change in the organic world.

_Uniformity of change considered, thirdly, in reference to

subterranean movements._--Thirdly, to pass on to the last of the

three topics before proposed for discussion, the reader will find, in

the account given in the Second Book, Vol. II., of the earthquakes

recorded in history, that certain countries have, from time immemorial,

been rudely shaken again and again; while others, comprising by

far the largest part of the globe, have remained to all appearance

motionless. In the regions of convulsion rocks have been rent asunder,

the surface has been forced up into ridges, chasms have opened, or the

ground throughout large spaces has been permanently lifted up above

or let down below its former level. In the regions of tranquillity

some areas have remained at rest, but others have been ascertained,

by a comparison of measurements made at different periods, to have

arisen by an insensible motion, as in Sweden, or to have subsided very

slowly, as in Greenland. That these same movements, whether ascending

or descending, have continued for ages in the same direction has been

established by historical or geological evidence. Thus we find on the

opposite coasts of Sweden that brackish water deposits, like those

now forming in the Baltic, occur on the eastern side, and upraised

strata filled with purely marine shells, now proper to the ocean, on

the western coast. Both of these have been lifted up to an elevation

of several hundred feet above high-water mark. The rise within the

historical period has not amounted to many yards, but the greater

extent of antecedent upheaval is proved by the occurrence in inland

spots, several hundred feet high, of deposits filled with fossil shells

of species now living either in the ocean or the Baltic.

It must in general be more difficult to detect proofs of slow and

gradual subsidence than of elevation, but the theory which accounts for

the form of circular coral reefs and lagoon islands, and which will

be explained in the concluding chapter of this work, will satisfy the

reader that there are spaces on the globe, several thousand miles in

circumference, throughout which the downward movement has predominated

for ages, and yet the land has never, in a single instance, gone down

suddenly for several hundred feet at once. Yet geology demonstrates

that the persistency of subterranean movements in one direction has

not been perpetual throughout all past time. There have been great

oscillations of level, by which a surface of dry land has been

submerged to a depth of several thousand feet, and then at a period

long subsequent raised again and made to emerge. Nor have the regions

now motionless been always at rest; and some of those which are at

present the theatres of reiterated earthquakes have formerly enjoyed

a long continuance of tranquillity. But, although disturbances have

ceased after having long prevailed, or have recommenced after a

suspension of ages, there has been no universal disruption of the

earth’s crust or desolation of the surface since times the most

remote. The non-occurrence of such a general convulsion is proved by

the perfect horizontality now retained by some of the most ancient

fossiliferous strata throughout wide areas.

That the subterranean forces have visited different parts of the globe

at successive periods is inferred chiefly from the unconformability of

strata belonging to groups of different ages. Thus, for example, on the

borders of Wales and Shropshire, we find the slaty beds of the ancient

Silurian system inclined and vertical, while the beds of the overlying

carboniferous shale and sandstone are horizontal. All are agreed that

in such a case the older set of strata had suffered great disturbance

before the deposition of the newer or carboniferous beds, and that

these last have never since been violently fractured, nor have ever

been bent into folds, whether by sudden or continuous lateral pressure.

On the other hand, the more ancient or Silurian group suffered only a

local derangement, and neither in Wales nor elsewhere are all the rocks

of that age found to be curved or vertical.

In various parts of Europe, for example, and particularly near Lake

Wener in the south of Sweden, and in many parts of Russia, the

Silurian strata maintain the most perfect horizontality; and a similar

observation may be made respecting limestones and shales of like

antiquity in the great lake district of Canada and the United States.

These older rocks are still as flat and horizontal as when first

formed; yet, since their origin, not only have most of the actual

mountain-chains been uplifted, but some of the very rocks of which

those mountains are composed have been formed, some of them by igneous

and others by aqueous action.

It would be easy to multiply instances of similar unconformability

in formations of other ages; but a few more will suffice. The

carboniferous rocks before alluded to as horizontal on the borders

of Wales are vertical in the Mendip hills in Somersetshire, where

the overlying beds of the New Red Sandstone are horizontal. Again,

in the Wolds of Yorkshire the last-mentioned sandstone supports on

its curved and inclined beds the horizontal Chalk. The Chalk again is

vertical on the flanks of the Pyrenees, and the tertiary strata repose

unconformably upon it.

As almost every country supplies illustrations of the same phenomena,

they who advocate the doctrine of alternate periods of disorder and

repose may appeal to the facts above described, as proving that every

district has been by turns convulsed by earthquakes and then respited

for ages from convulsions. But so it might with equal truth be affirmed

that every part of Europe has been visited alternately by winter and

summer, although it has always been winter and always summer in some

part of the planet, and neither of these seasons has ever reigned

simultaneously over the entire globe. They have been always shifting

from place to place; but the vicissitudes which recur thus annually

in a single spot are never allowed to interfere with the invariable

uniformity of seasons throughout the whole planet.

So, in regard to subterranean movements, the theory of the perpetual

uniformity of the force which they exert on the earth’s crust is quite

consistent with the admission of their alternate development and

suspension for long and indefinite periods within limited geographical

areas.

If, for reasons before stated, we assume a continual extinction of

species and appearance of others on the globe, it will then follow

that the fossils of strata formed at two distant periods on the same

spot will differ even more certainly than the mineral composition of

those strata. For rocks of the same kind have sometimes been reproduced

in the same district after a long interval of time; whereas all the

evidence derived from fossil remains is in favour of the opinion that

species which have once died out have never been reproduced. The

submergence, then, of land must be often attended by the commencement

of a new class of sedimentary deposits, characterized by a new set of

fossil animals and plants, while the reconversion of the bed of the sea

into land may arrest at once and for an indefinite time the formation

of geological monuments. Should the land again sink, strata will again

be formed; but one or many entire revolutions in animal or vegetable

life may have been completed in the interval.

As to the want of completeness in the fossiliferous series, which

may be said to be almost universal, we have only to reflect on what

has been already said of the laws governing sedimentary deposition,

and those which give rise to fluctuations in the animate world, to

be convinced that a very rare combination of circumstances can alone

give rise to such a superposition and preservation of strata as will

bear testimony to the gradual passage from one state of organic life

to another. To produce such strata nothing less will be requisite

than the fortunate coincidence of the following conditions: first, a

never-failing supply of sediment in the same region throughout a period

of vast duration; secondly, the fitness of the deposit in every part

for the permanent preservation of imbedded fossils; and, thirdly, a

gradual subsidence to prevent the sea or lake from being filled up and

converted into land.

It will appear in the chapter on coral reefs, that, in certain parts

of the Pacific and Indian Oceans, most of these conditions, if not

all, are complied with, and the constant growth of coral, keeping

pace with the sinking of the bottom of the sea, seems to have gone on

so slowly, for such indefinite periods, that the signs of a gradual

change in organic life might probably be detected in that quarter of

the globe if we could explore its submarine geology. Instead of the

growth of coralline limestone, let us suppose, in some other place,

the continuous deposition of fluviatile mud and sand, such as the

Ganges and Brahmapootra have poured for thousands of years into the

Bay of Bengal. Part of this bay, although of considerable depth,

might at length be filled up before an appreciable amount of change

was effected in the fish, mollusca, and other inhabitants of the sea

and neighbouring land. But if the bottom be lowered by sinking at

the same rate that it is raised by fluviatile mud, the bay can never

be turned into dry land. In that case one new layer of matter may be

superimposed upon another for a thickness of many thousand feet, and

the fossils of the inferior beds may differ greatly from those entombed

in the uppermost, yet every intermediate gradation may be indicated in

the passage from an older to a newer assemblage of species. Granting,

however, that such an unbroken sequence of monuments may thus be

elaborated in certain parts of the sea, and that the strata happen

to be all of them well adapted to preserve the included fossils from

decomposition, how many accidents must still concur before these

submarine formations will be laid open to our investigation! The whole

deposit must first be raised several thousand feet, in order to bring

into view the very foundation; and during the process of exposure the

superior beds must not be entirely swept away by denudation.

In the first place, the chances are nearly as three to one against

the mere emergence of the mass above the waters, because nearly

three-fourths of the globe are covered by the ocean. But if it be

upheaved and made to constitute part of the dry land, it must also,

before it can be available for our instruction, become part of that

area already surveyed by geologists. In this small fraction of land

already explored, and still very imperfectly known, we are required to

find a set of strata deposited under peculiar conditions, and which,

having been originally of limited extent, would have been probably much

lessened by subsequent denudation.

Yet it is precisely because we do not encounter at every step the

evidence of such gradations from one state of the organic world to

another, that so many geologists have embraced the doctrine of great

and sudden revolutions in the history of the animate world. Not content

with simply availing themselves, for the convenience of classification,

of those gaps and chasms which here and there interrupt the continuity

of the chronological series, as at present known, they deduce, from the

frequency of these breaks in the chain of records, an irregular mode of

succession in the events themselves, both in the organic and inorganic

world. But, besides that some links of the chain which once existed are

now entirely lost and others concealed from view, we have good reason

to suspect that it was never complete originally. It may undoubtedly be

said that strata have been always forming somewhere, and therefore at

every moment of past time Nature has added a page to her archives; but,

in reference to this subject, it should be remembered that we can never

hope to compile a consecutive history by gathering together monuments

which were originally detached and scattered over the globe. For, as

the species of organic beings contemporaneously inhabiting remote

regions are distinct, the fossils of the first of several periods which

may be preserved in any one country, as in America for example, will

have no connection with those of a second period found in India, and

will therefore no more enable us to trace the signs of a gradual change

in the living creation, than a fragment of Chinese history will fill up

a blank in the political annals of Europe.

The absence of any deposits of importance containing recent shells in

Chili, or anywhere on the western shore of South America, naturally led

Mr. Darwin to the conclusion that “where the bed of the sea is either

stationary or rising, circumstances are far less favourable than where

the level is sinking to the accumulation of conchiferous strata of

sufficient thickness and extension to resist the average vast amount

of denudation.” In like manner the beds of superficial sand, clay, and

gravel, with recent shells, on the coasts of Norway and Sweden, where

the land has risen in Post-tertiary times, are so thin and scanty as to

incline us to admit a similar proposition. We may in fact assume that

in all cases where the bottom of the sea has been undergoing continuous

elevation, the total thickness of sedimentary matter accumulating

at depths suited to the habitation of most of the species of shells

can never be great, nor can the deposits be thickly covered with

superincumbent matter, so as to be consolidated by pressure. When they

are upheaved, therefore, the waves on the beach will bear down and

disperse the loose materials; whereas, if the bed of the sea subsides

slowly, a mass of strata containing abundance of such species as live

at moderate depths, may be formed and may increase in thickness to any

amount. It may also extend horizontally over a broad area, as the water

gradually encroaches on the subsiding land.

Hence it will follow that great violations of continuity in the

chronological series of fossiliferous rocks will always exist, and the

imperfection of the record, though lessened, will never be removed by

future discoveries. For not only will no deposits originate on the

dry land, but those formed in the sea near land, which is undergoing

constant upheaval, will usually be too slight in thickness to endure

for ages.

In proportion as we become acquainted with larger geographical

areas, many of the gaps, by which a chronological table is rendered

defective, will be removed. We were enabled by aid of the labours of

Prof. Sedgwick and Sir Roderick Murchison, to intercalate, in 1838,

the marine strata of the Devonian period, with their fossil shells,

corals, and fish, between the Silurian and Carboniferous rocks.

Previously the marine fauna of these last-mentioned formations wanted

the connecting links which now render the passage from the one to

the other much less abrupt. In like manner the Upper Miocene has no

representative in England, but in France, Germany, and Switzerland it

constitutes a most instructive link between the living creation and the

middle of the great Tertiary period. Still we must expect, for reasons

before stated, that chasms will forever continue to occur, in some

parts of our sedimentary series.

_Concluding remarks on the consistency of the theory of gradual

change with the existence of great breaks in the series._--To

return to the general argument pursued in this chapter, it is assumed,

for reasons above explained, that a slow change of species is in

simultaneous operation everywhere throughout the habitable surface

of sea and land; whereas the fossilization of plants and animals is

confined to those areas where new strata are produced. These areas,

as we have seen, are always shifting their position, so that the

fossilizing process, by means of which the commemoration of the

particular state of the organic world, at any given time, is effected,

may be said to move about, visiting and revisiting different tracts in

succession.

To make still more clear the supposed working of this machinery, I

shall compare it to a somewhat analogous case that might be imagined

to occur in the history of human affairs. Let the mortality of the

population of a large country represent the successive extinction

of species, and the births of new individuals the introduction of

new species. While these fluctuations are gradually taking place

everywhere, suppose commissioners to be appointed to visit each

province of the country in succession, taking an exact account of the

number, names and individual peculiarities of all the inhabitants,

and leaving in each district a register containing a record of this

information. If, after the completion of one census, another is

immediately made on the same plan, and then another, there will at

last be a series of statistical documents in each province. When

those belonging to any one province are arranged in chronological

order, the contents of such as stand next to each other will differ

according to the length of the intervals of time between the taking of

each census. If, for example, there are sixty provinces, and all the

registers are made in a single year and renewed annually, the number

of births and deaths will be so small, in proportion to the whole

of the inhabitants, during the interval between the compiling of two

consecutive documents, that the individuals described in such documents

will be nearly identical; whereas, if the survey of each of the sixty

provinces occupies all the commissioners for a whole year, so that they

are unable to revisit the same place until the expiration of sixty

years, there will then be an almost entire discordance between the

persons enumerated in two consecutive registers in the same province.

There are, undoubtedly, other causes, besides the mere quantity of

time, which may augment or diminish the amount of discrepancy. Thus,

at some periods, a pestilential disease may have lessened the average

duration of human life; or a variety of circumstances may have caused

the births to be unusually numerous, and the population to multiply;

or a province may be suddenly colonized by persons migrating from

surrounding districts.

These exceptions may be compared to the accelerated rate of

fluctuations in the fauna and flora of a particular region, in which

the climate and physical geography may be undergoing an extraordinary

degree of alteration.

But I must remind the reader that the case above proposed has no

pretensions to be regarded as an exact parallel to the geological

phenomena which I desire to illustrate; for the commissioners are

supposed to visit the different provinces in rotation; whereas the

commemorating processes by which organic remains become fossilized,

although they are always shifting from one area to the other, are yet

very irregular in their movements. They may abandon and revisit many

spaces again and again, before they once approach another district;

and, besides this source of irregularity, it may often happen that,

while the depositing process is suspended, denudation may take place,

which may be compared to the occasional destruction by fire or other

causes of some of the statistical documents before mentioned. It is

evident that where such accidents occur the want of continuity in the

series may become indefinitely great, and that the monuments which

follow next in succession will by no means be equidistant from each

other in point of time.

If this train of reasoning be admitted, the occasional distinctness of

the fossil remains, in formations immediately in contact, would be a

necessary consequence of the existing laws of sedimentary deposition

and subterranean movement, accompanied by a constant dying-out and

renovation of species.

As all the conclusions above insisted on are directly opposed to

opinions still popular, I shall add another comparison, in the hope of

preventing any possible misapprehension of the argument. Suppose we

had discovered two buried cities at the foot of Vesuvius, immediately

superimposed upon each other, with a great mass of tuff and lava

intervening, just as Portici and Resina, if now covered with ashes,

would overlie Herculaneum. An antiquary might possibly be entitled to

infer, from the inscriptions on public edifices, that the inhabitants

of the inferior and older city were Greeks, and those of the modern

town Italians. But he would reason very hastily if he also concluded

from these data, that there had been a sudden change from the Greek

to the Italian language in Campania. But if he afterwards found three

buried cities, one above the other, the intermediate one being Roman,

while, as in the former example, the lowest was Greek and the uppermost

Italian, he would then perceive the fallacy of his former opinion and

would begin to suspect that the catastrophes, by which the cities

were inhumed, might have no relation whatever to the fluctuations in

the language of the inhabitants; and that, as the Roman tongue had

evidently intervened between the Greek and Italian, so many other

dialects may have been spoken in succession, and the passage from the

Greek to the Italian may have been very gradual, some terms growing

obsolete, while others were introduced from time to time.

If this antiquary could have shown that the volcanic paroxysms of

Vesuvius were so governed as that cities should be buried one above the

other, just as often as any variation occurred in the language of the

inhabitants, then, indeed, the abrupt passage from a Greek to a Roman,

and from a Roman to an Italian city, would afford proof of fluctuations

no less sudden in the language of the people.

So, in Geology, if we could assume that it is part of the plan of

Nature to preserve, in every region of the globe, an unbroken series

of monuments to commemorate the vicissitudes of the organic creation,

we might infer the sudden extirpation of species, and the simultaneous

introduction of others, as often as two formations in contact are found

to include dissimilar organic fossils. But we must shut our eyes to the

whole economy of the existing causes, aqueous, igneous, and organic,

if we fail to perceive that such is not the plan of Nature.

I shall now conclude the discussion of a question with which we have

been occupied since the beginning of the fifth chapter--namely, whether

there has been any interruption, from the remotest periods, of one

uniform and continuous system of change in the animate and inanimate

world. We were induced to enter into that inquiry by reflecting how

much the progress of opinion in Geology had been influenced by the

assumption that the analogy was slight in kind, and still more slight

in degree, between the causes which produced the former revolutions

of the globe, and those now in every-day operation. It appeared clear

that the earlier geologists had not only a scanty acquaintance with

existing changes, but were singularly unconscious of the amount of

their ignorance. With the presumption naturally inspired by this

unconsciousness, they had no hesitation in deciding at once that time

could never enable the existing powers of nature to work out changes

of great magnitude, still less such important revolutions as those

which are brought to light by Geology. They therefore felt themselves

at liberty to indulge their imaginations in guessing at what might be,

rather than inquiring what is; in other words, they employed themselves

in conjecturing what might have been the course of Nature at a remote

period, rather than in the investigation of what was the course of

Nature in their own times.

It appeared to them far more philosophical to speculate on the

possibilities of the past, than patiently to explore the realities of

the present; and having invented theories under the influences of such

maxims, they were consistently unwilling to test their validity by the

criterion of their accordance with the ordinary operations of Nature.

On the contrary, the claims of each new hypothesis to credibility

appeared enhanced by the great contrast, in kind or intensity, of the

causes referred to and those now in operation.

Never was there a dogma more calculated to foster indolence, and

to blunt the keen edge of curiosity, than this assumption of the

discordance between the ancient and existing causes of change. It

produced a state of mind unfavourable in the highest degree to the

candid reception of the evidence of those minute but incessant

alterations which every part of the earth’s surface is undergoing,

and by which the condition of its living inhabitants is continually

made to vary. The student, instead of being encouraged with the

hope of interpreting the enigmas presented to him in the earth’s

structure--instead of being prompted to undertake laborious inquiries

into the natural history of the organic world, and the complicated

effects of the igneous and aqueous causes now in operation--was taught

to despond from the first. Geology, it was affirmed, could never rise

to the rank of an exact science; the greater number of phenomena

must forever remain inexplicable, or only be partially elucidated by

ingenious conjectures. Even the mystery which invested the subject was

said to constitute one of its principal charms, affording, as it did,

full scope to the fancy to indulge in a boundless field of speculation.

The course directly opposed to this method of philosophizing consists

in an earnest and patient inquiry, how far geological appearances are

reconcilable with the effect of changes now in progress, or which

may be in progress in regions inaccessible to us, but of which the

reality is attested by volcanoes and subterranean movements. It also

endeavours to estimate the aggregate result of ordinary operations

multiplied by time, and cherishes a sanguine hope that the resources

to be derived from observation and experiment, or from the study of

Nature such as she now is, are very far from being exhausted. For this

reason all theories are rejected which involve the assumption of sudden

and violent catastrophes and revolutions of the whole earth, and its

inhabitants--theories which are restrained by no reference to existing

analogies, and in which a desire is manifested to cut, rather than

patiently to untie, the Gordian knot.

We have now, at least, the advantage of knowing, from experience, that

an opposite method has always put geologists on the road that leads

to truth--suggesting views which, although imperfect at first, have

been found capable of improvement, until at last adopted by universal

consent; while the method of speculating on a former distinct state of

things and causes has led invariably to a multitude of contradictory

systems, which have been overthrown one after the other--have been

found incapable of modification--and which have often required to be

precisely reversed.

The remainder of this work will be devoted to an investigation of the

changes now going on in the crust of the earth and its inhabitants.

The importance which the student will attach to such researches will

mainly depend on the degree of confidence which he feels in the

principles above expounded. If he firmly believes in the resemblance

or identity of the ancient and present system of terrestrial changes,

he will regard every fact collected respecting the causes in diurnal

action as affording him a key to the interpretation of some mystery in

the past. Events which have occurred at the most distant periods in

the animate and inanimate world will be acknowledged to throw light

on each other, and the deficiency of our information respecting some

of the most obscure parts of the present creation will be removed.

For as, by studying the external configuration of the existing land

and its inhabitants, we may restore in imagination the appearance of

the ancient continents which have passed away, so may we obtain from

the deposits of ancient seas and lakes an insight into the nature

of the subaqueous processes now in operation, and of many forms of

organic life which, though now existing, are veiled from sight. Rocks,

also, produced by subterranean fire in former ages, at great depths

in the bowels of the earth, present us, when upraised by gradual

movements, and exposed to the light of heaven, with an image of those

changes which the deep-seated volcano may now occasion in the nether

regions. Thus, although we are mere sojourners on the surface of the

planet, chained to a mere point in space, enduring but for a moment of

time, the human mind is not only enabled to number worlds beyond the

unassisted ken of mortal eye, but to trace the events of indefinite

ages before the creation of our race, and is not even withheld from

penetrating into the dark secrets of the ocean, or the interior of

the solid globe; free, like the spirit which the poet described as

animating the universe,

--_ire per omnes_

_Terrasque, tractusque maris, coelumque profundum_.

FOOTNOTES:

[Footnote 31: From the _Principles of Geology_, Bk. I, Ch. XIII.]

XXIX

CHARLES DARWIN

1809-1882

_Charles Robert Darwin, the grandson of Erasmus Darwin, was born at

Shrewsbury, England, February 12, 1809. He studied at both Edinburgh

and Cambridge, and graduated from the latter in 1831. From 1831 to 1836

he served as a naturalist on the “Beagle,” which made a trip around the

world in the interests of science. The voyage served as a post-graduate

course for Darwin, who then first adopted his evolutionary ideas and

developed as an original investigator. Reading Malthus, in 1838, on

the problem of population and the food supply, he integrated Malthus’

ideas into his own views of biology. In 1844 be began his “Origin of

Species,” which he completed in 1859. In 1858 he received a paper

from Alfred Russell Wallace, then in the Malay Archipelago, which

proposed the same theory of natural selection. Darwin believed that

when organisms increased much faster than the means of subsistence,

the ratios varied, and in the conditions produced by these natural

causes only those organisms survived which were best fitted to their

environment. He applied his concept to human evolution in his “Descent

of Man,” published in 1871. He died April 19, 1882, and was buried in

Westminster Abbey._

NATURAL SELECTION[32]

How will the struggle for existence, briefly discussed in the last

chapter, act in regard to variation? Can the principle of selection,

which we have seen is so potent in the hands of man, apply under

nature? I think we shall see that it can act most efficiently. Let

the endless number of slight variations and individual differences

occurring in our domestic productions, and, in a lesser degree, in

those under nature, be borne in mind; as well as the strength of the

hereditary tendency. Under domestication, it may be truly said that the

whole organization becomes in some degree plastic. But the variability,

which we almost universally meet with in our domestic production, is

not directly produced, as Hooker and Asa Gray have well remarked, by

man; he can neither originate varieties, nor prevent their occurrence;

he can only preserve and accumulate such as do occur. Unintentionally

he exposes organic beings to new and changing conditions of life, and

variability ensues; but similar changes of conditions might and do

occur under nature. Let it also be borne in mind how infinitely complex

and close-fitting are the mutual relations of all organic beings to

each other and to their physical conditions of life; and consequently

what infinitely varied diversities of structure might be of use to

each being under changing conditions of life. Can it then be thought

improbable, seeing that variations useful to man have undoubtedly

occurred, that other variations useful in some way to each being in the

great and complex battle of life, should occur in the course of many

successive generations? If such do occur, can we doubt (remembering

that many more individuals are born than can possibly survive) that

individuals having any advantage, however slight, over others, would

have the best chance of surviving and of procreating their kind? On the

other hand, we may feel sure that any variation in the least degree

injurious would be rigidly destroyed. This preservation of favourable

individual differences and variations, and the destruction of those

which are injurious, I have called Natural Selection, or the Survival

of the Fittest. Variations neither useful nor injurious would not be

affected by natural selection, and would be left either a fluctuating

element, as perhaps we see in certain polymorphic species, or would

ultimately become fixed, owing to the nature of the organism and the

nature of the conditions.