Chapter III: Part 3

There is no reason why the principles which have acted so efficiently under domestication should not have acted under Nature. In the survival of favoured individuals and races, during the constantly recurrent struggle for existence, we see a powerful and ever-acting form of selection. The struggle for existence inevitably follows from the high geometrical ratio of increase which is common to all organic beings. This high rate of increase is proved by calculation; by the rapid increase of many animals and plants during a succession of peculiar seasons and when naturalised in new countries. More individuals are born than can possibly survive. A grain in the balance may determine which individuals shall live and which shall die; which variety or species shall increase in number, and which shall decrease, or finally become extinct.

As the individuals of the same species come in all respects into the closest competition with each other, the struggle will generally be most severe between them; it will be almost equally severe between the varieties of the same species, and next in severity between the species of the same genus. On the other hand, the struggle will often be severe between beings remote in the scale of Nature. The slightest advantage in certain individuals, at any age or during any season, over those with which they come into competition, or better adaptation, in however slight a degree, to the surrounding physical conditions, will, in the long run, turn the balance.

With animals having separated sexes, there will be in most cases a struggle between the males for the possession of the females. The most vigorous males, or those which have most successfully struggled with their conditions of life, will generally leave most progeny. But success will often depend on the males having special weapons, or means of defence, or charms; and a slight advantage will lead to victory.

As geology plainly proclaims that each land has undergone great physical changes, we might have expected to find that organic beings have varied under Nature in the same way as they have varied under domestication. And if there has been any variability under Nature, it would be an unaccountable fact if natural selection had not come into play. It has often been asserted, but the assertion is incapable of proof, that the amount of variation under Nature is a strictly limited quantity. Man, though acting on external characters alone, and often capriciously, can produce within a short period a great result by adding up mere individual differences in his domestic productions; and everyone admits that species present individual differences. But, besides such differences, all naturalists admit that natural varieties exist, which are considered sufficiently distinct to be worthy of record in systematic works.

No one has drawn any clear distinction between individual differences and slight varieties, or between more plainly marked varieties and sub-species and species. On separate continents, and on different parts of the same continent when divided by barriers of any kind, what a multitude of forms exist which some experienced naturalists rank as varieties, others as geographical races or sub-species, and others as distinct, though closely allied species!

If, then, animals and plants do vary, let it be ever so slightly or slowly, why should not variations or individuals, differences which are in any way beneficial, be preserved and accumulated through natural selection, or the survival of the fittest? If man can, by patience, select variations useful to him, why, under changing and complex conditions of life, should not variations useful to Nature's living products often arise, and be preserved, or selected? What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature--favouring the good and rejecting the bad? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life.

In the future I see open fields for far more important researches. Psychology will be based on the foundation already well laid by Mr. Herbert Spencer--that of the necessary acquirement of each mental power and capacity by gradation. Much light will be thrown on the origin of man and his history.

Authors of the highest eminence seem to be fully satisfied with the view that each species has been independently created. To my mind it accords better with what we know of the laws impressed on matter by the Creator that the production and extinction of the past and present inhabitants of the world should have been due to secondary causes, like those determining the birth and death of the individual. When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled. Judging from the past, we may safely infer that not one living species will transmit its unaltered likeness to a distant futurity.

Of the species now living very few will transmit progeny of any kind to a far distant futurity; for the manner in which all organic beings are grouped shows that the greater number of species in each genus, and all the species in many genera, have left no descendants, but have become utterly extinct. We can so far take a prophetic glance into futurity as to foretell that it will be the common and widely-spread species, belonging to the larger and dominant groups within each class, which will ultimately prevail and procreate new and dominant species. As all the living forms of life are the lineal descendants of those which lived long before the Cambrian epoch, we may feel certain that the ordinary succession by generation has never once been broken, and that no cataclysm has desolated the whole world. We may look with some confidence to a secure future of great length. As natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection.

It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance, which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a ratio of increase so high as to lead to a struggle for life, and, as a consequence, to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. Thus, from the war of Nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms, or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.

SIR HUMPHRY DAVY

Elements of Chemical Philosophy

Humphry Davy, the celebrated natural philosopher, was born Dec. 17,
1778, at Penzance, England. At the age of seventeen he became an
apothecary's apprentice, and at the age of nineteen assistant at
Dr. Beddoes's pneumatic institution at Bristol. During researches
at the pneumatic institution he discovered the physiological
effects of "laughing gas," and made so considerable a reputation as
a chemist that at the age of twenty-two he was appointed lecturer,
and a year later professor, at the Royal Institution. For ten
years, from 1803, he was engaged in agricultural researches, and in
1813 published his "Elements of Agricultural Chemistry." During the
same decade he conducted important investigations into the nature
of chemical combination, and succeeded in isolating the elements
potassium, sodium, strontium, magnesium, and chlorine. In 1812 he
was knighted, and married Mrs. Apreece, _née_ Jane Kerr. In 1815 he
investigated the nature of fire-damp and invented the Davy safety
lamp. In 1818 he received a baronetcy, and two years later was
elected President of the Royal Society. On May 29, 1829, he died at
Geneva. Davy's "Elements of Chemical Philosophy," of which a
summary is given here, was published in one volume in 1812, being
the substance of lectures delivered before the Board of
Agriculture.

_I.--Forms and Changes of Matter_

The forms and appearances of the beings and substances of the external world are almost infinitely various, and they are in a state of continued alteration. In general, matter is found in four forms, as (1) solids, (2) fluids, (3) gases, (4) ethereal substances.

1. _Solids._ Solids retain whatever mechanical form is given to them; their parts are separated with difficulty, and cannot readily be made to unite after separation. They may be either elastic or non-elastic, and differ in hardness, in colour, in opacity, in density, in weight, and, if crystalline, in crystalline form.

2. _Fluids._ Fluids, when in small masses, assume the spherical form; their parts possess freedom of motion; they differ in density and tenacity, in colour, and in opacity. They are usually regarded as incompressible; at least, a very great mechanical force is required to compress them.

3. _Gases._ Gases exist free in the atmosphere, but may be confined. Their parts are highly movable; they are compressible and expansible, and their volumes are inversely as the weight compressing them. All known gases are transparent, and present only two or three varieties of colour; they differ materially in density.

4. _Ethereal Substances._ Ethereal substances are known to us only in their states of motion when acting upon our organs of sense, or upon other matter, and are not susceptible of being confined. It cannot be doubted that there is such matter in motion in space. Ethereal matter differs either in its nature, or in its affections by motion, for it produces different effects; for instance, radiant heat, and different kinds of light.

All these forms of matter are under the influence of active forces, such as gravitation, cohesion, heat, chemical and electrical attraction, and these we must now consider.

1. _Gravitation._ When a stone is thrown into the atmosphere, it rapidly descends towards the earth. This is owing to gravitation. All the great bodies in the universe are urged towards each other by a similar force. Bodies mutually gravitate towards each other, but the smaller body proportionately more than the larger one; hence the power of gravity is said to vary directly as the mass. Gravitation also varies with distance, and acts inversely as the square of the distance.

2. _Cohesion._ Cohesion is the force which preserves the forms of solids, and gives globularity to fluids. It is usually said to act only at the surface of bodies or by their immediate contact; but this does not seem to be the case. It certainly acts with much greater energy at small distances, but the spherical form of minute portions of fluid matter can be produced only by the attractions of all the parts of which they are composed, for each other; and most of these attractions must be exerted at sensible distances, so that gravitation and cohesion may be mere modifications of the same general power of attraction.

3. _Heat._ When a body which occasions the sensation of heat on our organs is brought into contact with another body which has no such effect, the hot body contracts and loses to a certain extent its power of communicating heat; and the other body expands. Different solids and fluids expand very differently when heated, and the expansive power of liquids, in general, is greater than that of solids.

It is evident that the density of bodies must be diminished by expansion; and in the case of fluids and gases, the parts of which are mobile, many important phenomena depend upon this circumstance. For instance, if heat be applied to fluids and gases, the heated parts change their places and rise, and the currents in the ocean and atmosphere are due principally to this movement. There are very few exceptions to the law of the expansion of bodies at the time they become capable of communicating the sensation of heat, and these exceptions seem to depend upon some chemical change in the constitution of bodies, or on their crystalline arrangements.

The power which bodies possess of communicating or receiving heat is known as _temperature_, and the temparature of a body is said to be high or low with respect to another in proportion as it occasions an expansion or contraction of its parts.

When equal volumes of different bodies of different temperatures are suffered to remain in contact till they acquire the same temperature, it is found that this temperature is not a mean one, as it would be in the case of equal volumes of the same body. Thus if a pint of quicksilver at 100° be mixed with a pint of water at 50°, the resulting temperature is not 75°, but 70°; the mercury has lost thirty degrees, whereas the water has only gained twenty degrees. This difference is said to depend on the different _capacities_ of bodies for heat.

Not only do different bodies vary in their capacity for heat, but they likewise acquire heat with very different degrees of celerity. This last difference depends on the different power of bodies for _conducting_ heat, and it will be found that as a rule the densest bodies, with the least capacity for heat, are the best conductors.

Heat, or the power of repulsion, may be considered as the _antagonist_ power to the attraction of cohesion. Thus solids by a certain increase of temperature become fluids, and fluids gases; and, _vice versâ_, by a diminution of temperature, gases become fluids, and fluids solids.

Proofs of the conversion of solids, fluids, or gases into ethereal substances are not distinct. Heated bodies become luminous and give off radiant heat, which affects the bodies at a distance, and it may therefore be held that particles are thrown off from heated bodies with great velocity, which, by acting on our organs, produce the sensations of heat or light, and that their motion, communicated to the particles of other bodies, has the power of expanding them. It may, however, be said that the radiant matters emitted by bodies in ignition are specific substances, and that common matter is not susceptible of assuming this form; or it may be contended that the phenomena of radiation do in fact, depend upon motions communicated to subtile matter everywhere existing in space.

The temperatures at which bodies change their states from fluids to solids, though in general definite, are influenced by a few circumstances such as motion and pressure.

When solids are converted into fluids, or fluids into gases, there is always a loss of heat of temperature; and, _vice versâ_, when gases are converted into fluids, or fluids into solids, there is an increase of heat of temperature, and in this case it is said that _latent_ heat is absorbed or given out.

The expansion due to heat has been accounted for by supposing a subtile fluid, or _caloric_, capable of combining with bodies and of separating their parts from each other, and the absorption and liberation of latent heat can be explained on this principle. But many other facts are incompatible with the theory. For instance, metal may be kept hot for any length of time by friction, so that if _caloric_ be pressed out it must exist in an inexhaustible quantity. Delicate experiments have shown that bodies, when heated, do not increase in weight.

It seems possible to account for all the phenomena of heat, if it be supposed that in solids the particles are in a constant state of vibratory motion, the particles of the hottest bodies moving with the greatest velocity and through the greatest space; that in fluids and gases the particles have not only vibratory motion, but also a motion round their own axes with different velocities, and that in ethereal substances the particles move round their own axes and separate from each other, penetrating in right lines through space. Temperature may be conceived to depend upon the velocity of the vibrations, increase of capacity on the motion being performed in greater space; and the diminution of temperature during the conversion of solids into fluids or gases may be explained on the idea of the loss of vibratory motion in consequence of the revolution of particles round their axes at the moment when the body becomes fluid or aeriform, or from the loss of rapidity of vibration in consequence of the motion of particles through greater space.

4. _Chemical Attraction._ Oil and water will not _combine_; they are said to have no chemical _attraction_ or _affinity_ for each other. But if oil and solution of potassa in water be mixed, the oil and the solution blend and form a soap; and they are said to attract each other chemically or to have a _chemical affinity_ for each other. It is a general character of chemical combination that it changes the qualities of the bodies. Thus, corrosive and pungent substances may become mild and tasteless; solids may become fluids, and solids and fluids gases.

No body will act chemically upon another body at any sensible distance; apparent contact is necessary for chemical action. A freedom of motion in the parts of the bodies or a want of cohesion greatly assists action, and it was formerly believed that bodies cannot act chemically upon each other unless one of them be fluid or gaseous.

Different bodies unite with different degrees of force, and hence one body is capable of separating others from certain of their combinations, and in consequence mutual decompositions of different compounds take place. This has been called _double affinity_, or _complex chemical affinity_.

As in all well-known compounds the proportions of the elements are in certain definite ratios to each other, it is evident that these ratios may be expressed by numbers; and if one number be employed to denote the smallest quantity in which a body combines, all other quantities of the same body will be multiples of this number, and the smallest proportions into which the undecomposed bodies enter into union being known, the constitution of the compounds they form may be learnt, and the element which unites chemically in the smallest quantity being expressed by unity, all the other elements may be represented by the relations of their quantities to unity.

5. _Electrical Attraction._ A piece of dry silk briskly rubbed against a warm plate of polished flint glass acquires the property of adhering to the glass, and both the silk and the glass, if apart from each other, attract light substances. The bodies are said to be _electrically excited_. Probably, all bodies which differ from each other become electrically excited when rubbed and pressed together. The electrical excitement seems of two kinds. A pith-ball touched by glass excited by silk repels a pith-ball touched by silk excited by metals. Electrical excitement of the same nature as that in glass excited by silk is known as _vitreous_ or _positive_, and electrical excitement of the opposite nature is known as _resinous_ or _negative_.

A rod of glass touched by an electrified body is electrified only round the point of contact. A rod of metal, on the contrary, suspended on a rod of glass and brought into contact with an electrical surface, instantly becomes electrical throughout. The glass is said to be a _non-conductor_, or _insulating substance_; the metal a _conductor_.

When a non-conductor or imperfect conductor, provided it be a thin plate of matter placed upon a conductor, is brought in contact with an excited electrical body, the surface opposite to that of contact gains the opposite electricity from that of the excited body, and if the plate be removed it is found to possess two surfaces in opposite states. If a conductor be brought into the neighbourhood of an excited body--the air, which is a non-conductor, being between them--that extremity of the conductor which is opposite to the excited body gains the opposite electricity; and the other extremity, if opposite to a body connected with the ground, gains the same electricity, and the middle point is not electrical at all. This is known as _induced_ electricity.

The common exhibition of electrical effects is in attractions and repulsions; but electricity also produces chemical phenomena. If a piece of zinc and copper in contact with each other at one point be placed in contact at other points with the same portion of water, the zinc will corrode, and attract oxygen from the water much more rapidly than if it had not been in contact with the copper; and if sulphuric acid be added, globules of inflammable air are given off from the copper, though it is not dissolved or acted upon.

Chemical phenomena in connection with electrical effects can be shown even better by combinations in which the electrical effects are increased by alterations of different metals and fluids--the so-called _voltaic batteries_. Such are the decomposing powers of such batteries that not even insoluble compounds are capable of resisting their energy, for even glass, sulphate of baryta, fluorspar, etc., are slowly acted upon, and the alkaline, earthy, or acid matter carried to the poles in the common order.

The most powerful voltaic combinations are formed by substances that act chemically with most energy upon each other, and such substances as undergo no chemical changes in the combination exhibit no electrical powers. Hence it was supposed that the electrical powers of metals were entirely due to chemical changes; but this is not the case, for contact produces electricity even when no chemical change can be observed.

_II.--Radiant or Ethereal Matter_

When similar thermometers are placed in different parts of the solar beam, it is found that different effects are produced in the differently coloured rays. The greatest heat is exhibited in the red rays, the least in the violet rays; and in a space beyond the red rays, where there is no visible light, the increase of temperature is greatest of all.

From these facts it is evident that matter set in motion by the sun has the power of producing heat without light, and that its rays are less refrangible than the visible rays. The invisible rays that produce heat are capable of reflection as well as refraction in the same manner as the visible rays.

Rays capable of producing heat with and without light proceed not only from the sun, but also from bodies at the surface of the globe under peculiar agencies or changes. If, for instance, a thermometer be held near an ignited body, it receives an impression connected with an elevation of temperature; this is partly produced by the conducting powers of the air, and partly by an impulse which is instantaneously communicated, even to a considerable distance. This effect is called the radiation of terrestrial heat.

The manner in which the temperatures of bodies are affected by rays producing heat is different for different substances, and is very much connected with their colours. The bodies that absorb most light, and reflect least, are most heated when exposed either to solar or terrestrial rays. Black bodies are, in general, more heated than red; red more than green; green more than yellow; and yellow more than white. Metals are less heated than earthy or stony bodies, or than animal or vegetable matters. Polished surfaces are less heated than rough surfaces.

The bodies that have their temperatures most easily raised by heat rays are likewise those that are most easily cooled by their own radiation, or that at the same temperature emit most heat-making rays. Metals radiate less heat than glass, glass less than vegetable substances, and charcoal has the highest radiating powers of any body as yet made the subject of experiment.

Radiant matter has the power of producing chemical changes partly through its heating power, and partly through some other specific and peculiar influence. Thus chlorine and hydrogen detonate when a mixture of them is exposed to the solar beams, even though the heat is inadequate to produce detonation.

If moistened silver be exposed to the different rays of the solar spectrum, it will be found that no effect is produced upon it by the least refrangible rays which occasion heat without light; that a slight discoloration only will be produced by the red rays; that the effect of blackening will be greater towards the violet end of the spectrum; and that in a space beyond the violet, where there is no sensible heat or light, the chemical effect will be very distinct. There seem to be rays, therefore, more refrangible than the rays producing light and heat.

The general facts of the refraction and effects of the solar beam offer an analogy to the agencies of electricity.

In general, in Nature the effects of the solar rays are very compounded. Healthy vegetation depends upon the presence of the solar beams or of light, and while the heat gives fluidity and mobility to the vegetable juices, chemical effects are likewise occasioned, oxygen is separated from them, and inflammable compounds are formed. Plants deprived of light become white and contain an excess of saccharine and aqueous particles; and flowers owe the variety of their hues to the influence of the solar beams. Even animals require the presence of the rays of the sun, and their colours seem to depend upon the chemical influence of these rays.

Two hypotheses have been invented to account for the principal operations of radiant matter. In the first it is supposed that the universe contains a highly rare elastic substance, which, when put into a state of undulation, produces those effects on our organs of sight which constitute the sensations of vision and other phenomena caused by solar and terrestrial rays. In the second it is conceived that particles are emitted from luminous or heat-making bodies with great velocity, and that they produce their effects by communicating their motions to substances, or by entering into them and changing their composition.

Newton has attempted to explain the different refrangibility of the rays of light by supposing them composed of particles differing in size. The same great man has put the query whether light and common matter are not convertible into each other; and, adopting the idea that the phenomena of sensible heat depend upon vibrations of the particles of bodies, supposes that a certain intensity of vibrations may send off particles into free space, and that particles in rapid motion in right lines, in losing their own motion, may communicate a vibratory motion to the particles of terrestrial bodies.

MICHAEL FARADAY

Experimental Researches in Electricity

Michael Faraday was the son of a Yorkshire blacksmith, and was born
in London on September 22, 1791. At the age of twenty he became
assistant to Sir Humphry Davy, whose lectures he had attended at
the Royal Institution. Here he worked for the rest of his laborious
life, which closed on August 25, 1867. The fame of Faraday, among
those whose studies qualify them for a verdict, has risen steadily
since his death, great though it then was. His researches were of
truly epoch-making character, and he was the undisputed founder of
the modern science of electricity, which is rapidly coming to
dominate chemistry itself. Faraday excelled as a lecturer, and
could stand even the supreme test of lecturing to children.
Faraday's "Experimental Researches in Electricity" is a record of
some of the most brilliant experiments in the history of science.
In the course of his investigations he made discoveries which have
had momentous consequences. His discovery of the mutual relation of
magnets and of wires conducting electric currents was the beginning
of the modern dynamo and all that it involves; while his
discoveries of electric induction and of electrolysis were of equal
significance. Most of the researches are too technical for
epitomisation; but those given are representative of his manner and
methods.

_I.--Atmospheric Magnetism_

It is to me an impossible thing to perceive that two-ninths of the atmosphere by weight is a highly magnetic body, subject to great changes in its magnetic character, by variations in its temperature and condensation or rarefaction, without being persuaded that it has much to do with the variable disposition of the magnetic forces upon the surface of the earth.

The earth is a spheroidal body consisting of paramagnetic and diamagnetic substances irregularly disposed and intermingled; but for the present the whole may be considered a mighty compound magnet. The magnetic force of this great magnet is known to us only on the surface of the earth and water of our planet, and the variations in the magnetic lines of force which pass in or across this surface can be measured by their action on small standard magnets; but these variations are limited in their information, and do not tell us whether the cause is in the air above or the earth beneath.

The lines of force issue from the earth in the northern and southern parts and coalesce with each other over the equatorial, as would be the case in a globe having one or two short magnets adjusted in relation to its axis, and it is probable that the lines of force in their circuitous course may extend through space to tens of thousands of miles. The lines proceed through space with a certain degree of facility, but there may be variations in space, _e.g._, variations in its temperature which affect its power of transmitting the magnetic influence.

Between the earth and space, however, is interposed the atmosphere, and at the bottom of the atmosphere we live. The atmosphere consists of four volumes of nitrogen and one of oxygen uniformly mixed and acting magnetically as a single medium. The _nitrogen_ of the air is, as regards the magnetic force, neither paramagnetic nor diamagnetic, whether dense or rare, or at high or low temperatures.

The _oxygen_ of the air, on the other hand, is highly paramagnetic, being, bulk for bulk, equivalent to a solution of protosulphate of iron, containing of the crystallised salt seventeen times the weight of the oxygen. It becomes less paramagnetic, volume for volume, as it is rarefied, and apparently in the simple proportion of its rarefaction, the temperature remaining the same. When its temperature is raised--the expansion consequent thereon being permitted--it loses very greatly its paramagnetic force, and there is sufficient reason to conclude that when its temperature is lowered its paramagnetic condition is exalted. These characters oxygen preserves even when mingled with the nitrogen in the air.

Hence the atmosphere is a highly magnetic medium, and this medium is changed in its magnetic relations by every change in its density and temperature, and must affect both the intensity and direction of the magnetic force emanating from the earth, and may account for the variations which we find in terrestrial magnetic power.

We may expect as the sun leaves us on the west some magnetic effect correspondent to that of the approach of a body of cold air from the east. Again, the innumerable circumstances that break up more or less any average arrangement of the air temperatures may be expected to give not merely differences in the regularity, direction, and degree of magnetic variation, but, because of vicinity, differences so large as to be many times greater than the mean difference for a given short period, and they may also cause irregularities in the times of their occurrence. Yet again, the atmosphere diminishes in density upwards, and this diminution will affect the transmission of the electric force.

The result of the _annual variation_ that may be expected from the magnetic constitution and condition of the atmosphere seems to me to be of the following kind.

Since the axis of the earth's rotation is inclined 23° 28' to the plane of the ecliptic, the two hemispheres will become alternately warmer and cooler than each other. The air of the cooled hemisphere will conduct magnetic influence more freely than if in the mean state, and the lines of force passing through it will increase in amount, whilst in the other hemisphere the warmed air will conduct with less readiness than before, and the intensity will diminish. In addition to this effect of temperature, there ought to be another due to the increase of the ponderable portion of the air in the cooled hemisphere, consequent on its contraction and the coincident expansion of the air in the warmer half, both of which circumstances tend to increase the variation in power of the two hemispheres from the normal state. Then, as the earth rolls on its annual journey, that which was at one time the cooler becomes the warmer hemisphere, and in its turn sinks as far below the average magnetic intensity as it before had stood above it, while the other hemisphere changes its magnetic condition from less to more intense.

_II.--Electro-Chemical Action_

The theory of definite electrolytical or electro-chemical action appears to me to touch immediately upon the absolute quantity of electricity belonging to different bodies. As soon as we perceive that chemical powers are definite for each body, and that the electricity which we can loosen from each body has definite chemical action which can be measured, we seem to have found the link which connects the proportion of that we have evolved to the proportion belonging to the particles in their natural state.

Now, it is wonderful to observe how small a quantity of a compound body is decomposed by a certain quantity of electricity. One grain of water, for instance, acidulated to facilitate conduction, will require an electric current to be continued for three minutes and three-quarters to effect its decomposition, and the current must be powerful enough to keep a platina wire 1/104 inch in thickness red hot in the air during the whole time, and to produce a very brilliant and constant star of light if interrupted anywhere by charcoal points. It will not be too much to say that this necessary quantity of electricity is equal to a very powerful flash of lightning; and yet when it has performed its full work of electrolysis, it has separated the elements of only a single grain of water.

On the other hand, the relation between the conduction of the electricity and the decomposition of the water is so close that one cannot take place without the other. If the water be altered only in that degree which consists in its having the solid instead of the fluid state, the conduction is stopped and the decomposition is stopped with it. Whether the conduction be considered as depending upon the decomposition or not, still the relation of the two functions is equally intimate.

Considering this close and twofold relation--namely, that without decomposition transmission of electricity does not occur, and that for a given definite quantity of electricity passed an equally definite and constant quantity of water or other matter is decomposed; considering also that the agent, which is electricity, is simply employed in overcoming electrical powers in the body subjected to its action, it seems a probable and almost a natural consequence that the quantity which passes is the equivalent of that of the particles separated; _i.e._, that if the electrical power which holds the elements of a grain of water in combination, or which makes a grain of oxygen and hydrogen in the right proportions unite into water when they are made to combine, could be thrown into a current, it would exactly equal the current required for the separation of that grain of water into its elements again; in other words, that the electricity which decomposes and that which is evolved by the decomposition of a certain quantity of matter are alike.

This view of the subject gives an almost overwhelming idea of the extraordinary quantity or degree of electric power which naturally belongs to the particles of matter, and the idea may be illustrated by reference to the voltaic pile.

The source of the electricity in the voltaic instrument is due almost entirely to chemical action. Substances interposed between its metals are all electrolytes, and the current cannot be transmitted without their decomposition. If, now, a voltaic trough have its extremities connected by a body capable of being decomposed, such as water, we shall have a continuous current through the apparatus, and we may regard the part where the acid is acting on the plates and the part where the current is acting upon the water as the reciprocals of each other. In both parts we have the two conditions, _inseparable in such bodies as these_: the passing of a current, and decomposition. In the one case we have decomposition associated with a current; in the other, a current followed by decomposition.

Let us apply this in support of my surmise respecting the enormous electric power of each particle or atom of matter.

Two wires, one of platina, and one of zinc, each one-eighteenth of an inch in diameter, placed five-sixteenths of an inch apart, and immersed to the depth of five-eighths of an inch in acid, consisting of one drop of oil of vitriol and four ounces of distilled water at a temperature of about 60° Fahrenheit, and connected at the other ends by a copper wire eighteen feet long, and one-eighteenth of an inch in thickness, yielded as much electricity in little more than three seconds of time as a Leyden battery charged by thirty turns of a very large and powerful plate electric machine in full action. This quantity, although sufficient if passed at once through the head of a rat or cat to have killed it, as by a flash of lightning, was evolved by the mutual action of so small a portion of the zinc wire and water in contact with it that the loss of weight by either would be inappreciable; and as to the water which could be decomposed by that current, it must have been insensible in quantity, for no trace of hydrogen appeared upon the surface of the platina during these three seconds. It would appear that 800,000 such charges of the Leyden battery would be necessary to decompose a single grain of water; or, if I am right, to equal the quantity of electricity which is naturally associated with the elements of that grain of water, endowing them with their mutual chemical affinity.

This theory of the definite evolution and the equivalent definite action of electricity beautifully harmonises the associated theories of definite proportions and electro-chemical affinity.

According to it, the equivalent weights of bodies are simply those quantities of them which contain equal quantities of electricity, or have naturally equal electric powers, it being the electricity which _determines_ the equivalent number, _because_ it determines the combining force. Or, if we adopt the atomic theory or phraseology, then the atoms of bodies which are equivalent to each other in their ordinary chemical action have equal quantities of electricity naturally associated with them. I cannot refrain from recalling here the beautiful idea put forth, I believe, by Berzelius in his development of his views of the electro-chemical theory of affinity, that the heat and light evolved during cases of powerful combination are the consequence of the electric discharge which is at the moment taking place. The idea is in perfect accordance with the view I have taken of the quantity of electricity associated with the particles of matter.

The definite production of electricity in association with its definite action proves, I think, that the current of electricity in the voltaic pile is sustained by chemical decomposition, or, rather, by chemical action, and not by contact only. But here, as elsewhere, I beg to reserve my opinion as to the real action of contact.

Admitting, however, that chemical action is the source of electricity, what an infinitely small fraction of that which is active do we obtain and employ in our voltaic batteries! Zinc and platina wires one-eighteenth of an inch in diameter and about half an inch long, dipped into dilute sulphuric acid, so weak that it is not sensibly sour to the tongue, or scarcely sensitive to our most delicate test papers, will evolve more electricity in one-twentieth of a minute than any man would willingly allow to pass through his body at once.

The chemical energy represented by the satisfaction of the chemical affinities of a grain of water and four grains of zinc can evolve electricity equal in quantity to that of a powerful thunderstorm. Nor is it merely true that the quantity is active; it can be directed--made to perform its full equivalent duty. Is there not, then, great reason to believe that, by a closer investigation of the development and action of this subtile agent, we shall be able to increase the power of our batteries, or to invent new instruments which shall a thousandfold surpass in energy those we at present possess?

_III.--The Gymnotus, or Electric Eel_

Wonderful as are the laws and phenomena of electricity when made evident to us in inorganic or dead matter, their interest can bear scarcely any comparison with that which attaches to the same force when connected with the nervous system and with life.

The existence of animals able to give the same concussion to the living system as the electrical machine, the voltaic battery, and the thunderstorm being made known to us by various naturalists, it became important to identify their electricity with the electricity produced by man from dead matter. In the case of the _Torpedo_ [a fish belonging to the family of Electric Rings] this identity has been fully proved, but in the case of the _Gymnotus_ the proof has not been quite complete, and I thought it well to obtain a specimen of the latter fish.

A gymnotus being obtained, I conducted a series of experiments. Besides the hands two kinds of collectors of electricity were used--one with a copper disc for contact with the fish, and the other with a plate of copper bent into saddle shape, so that it might enclose a certain extent of the back and sides of the fish. These conductors, being put over the fish, collected power sufficient to produce many electric effects.

SHOCK. The shock was very powerful when the hands were placed one near the head and the other near the tail, and the nearer the hands were together, within certain limits, the less powerful was the shock. The disc conductors conveyed the shock very well when the hands were wetted.

GALVANOMETER. A galvanometer was readily affected by using the saddle conductors, applied to the anterior and posterior parts of the gymnotus. A powerful discharge of the fish caused a deflection of thirty or forty degrees. The deflection was constantly in a given direction, the electric current being always from the anterior part of the animal through the galvanometer wire to the posterior parts. The former were, therefore, for the time externally positive and the latter negative.

MAKING A MAGNET. When a little helix containing twenty-two feet of silked wire wound on a quill was put into a circuit, and an annealed steel needle placed in the helix, the needle became a magnet; and the direction of its polarity in every cast indicated a current from the anterior to the posterior parts of the gymnotus.

CHEMICAL DECOMPOSITION. Polar decomposition of a solution of iodide of potassium was easily obtained.

EVOLUTION OF HEAT. Using a Harris' thermo-electrometer, we thought we were able, in one instance, to observe a feeble elevation of temperature.

SPARK. By suitable apparatus a spark was obtained four times.

Such were the general electric phenomena obtained from the gymnotus, and on several occasions many of the phenomena were obtained together. Thus, a magnet was made, a galvanometer deflected, and, perhaps, a wire heated by one single discharge of the electric force of the animal. When the shock is strong, it is like that of a large Leyden battery charged to a low degree, or that of a good voltaic battery of, perhaps, one hundred or more pairs of plates, of which the circuit is completed for a moment only.

I endeavoured by experiment to form some idea of the quantity of electricity, and came to the conclusion that a single medium discharge of the fish is at least equal to the electricity of a Leyden battery of fifteen jars, containing 3,500 square inches of glass coated on both sides, charged to its highest degree. This conclusion is in perfect accordance with the degree of deflection which the discharge can produce in a galvanometer needle, and also with the amount of chemical decomposition produced in the electrolysing experiments.

The gymnotus frequently gives a double and even a triple shock, with scarcely a sensible interval between each discharge.

As at the moment of shock the anterior parts are positive and the posterior negative, it may be concluded that there is a current from the former to the latter through every part of the water which surrounds the animal, to a considerable distance from its body. The shock which is felt, therefore, when the hands are in the most favourable position is the effect of a very small portion only of the electricity which the animal discharges at the moment, by far the largest portion passing through the surrounding water.

This enormous external current must be accompanied by some effect within the fish _equivalent_ to a current, the direction of which is from the tail towards the head, and equal to the sum of _all these external_ forces. Whether the process of evolving or exciting the electricity within the fish includes the production of the internal current, which is not necessarily so quick and momentary as the external one, we cannot at present say; but at the time of the shock the animal does not apparently feel the electric sensation which he causes in those around him.

The gymnotus can stun and kill fish which are in very various relations to its own body. The extent of surface which the fish that is about to be struck offers to the water conducting the electricity increases the effect of the shock, and the larger the fish, accordingly, the greater must be the shock to which it will be subjected.

The Chemical History of a Candle

"The Chemical History of a Candle" was the most famous course in
the long and remarkable series of Christmas lectures, "adapted to a
juvenile auditory," at the Royal Institution, and remains a
rarely-approached model of what such lectures should be. They were
illustrated by experiments and specimens, but did not depend upon
these for coherence and interest. They were delivered in 1860-61,
and have just been translated, though all but half-a-century old,
into German.

_I.--Candles and their Flames_

There is not a law under which any part of this universe is governed that does not come into play in the phenomena of the chemical history of a candle. There is no better door by which you can enter into the study of natural philosophy than by considering the physical phenomena of a candle.

And now, my boys and girls, I must first tell you of what candles are made. Some are great curiosities. I have here some bits of timber, branches of trees particularly famous for their burning. And here you see a piece of that very curious substance taken out of some of the bogs in Ireland, called _candle-wood_--a hard, strong, excellent wood, evidently fitted for good work as a resister of force, and yet withal burning so well that, where it is found, they make splinters of it, and torches, since it burns like a candle, and gives a very good light indeed. And in this wood we have one of the most beautiful illustrations of the general nature of a candle that I can possibly give. The fuel provided, the means of bringing that fuel to the place of chemical action, the regular and gradual supply of air to that place of action--heat and light all produced by a little piece of wood of this kind, forming, in fact, a natural candle.

But we must speak of candles as they are in commerce. Here are a couple of candles commonly called dips. They are made of lengths of cotton cut off, hung up by a loop, dipped into melted tallow, taken out again and cooled; then re-dipped until there is an accumulation of tallow round the cotton. However, a candle, you know, is not now a greasy thing like an ordinary tallow candle, but a clean thing; and you may almost scrape off and pulverise the drops which fall from it without soiling anything.

The candle I have in my hand is a stearine candle, made of stearine from tallow. Then here is a sperm candle, which comes from the purified oil of the spermaceti whale. Here, also, are yellow beeswax and refined beeswax from which candles are made. Here, too, is that curious substance called paraffin, and some paraffin candles made of paraffin obtained from the bogs of Ireland. I have here also a substance brought from Japan, a sort of wax which a kind friend has sent me, and which forms a new material for the manufacture of candles.

Now, as to the light of the candle. We will light one or two, and set them at work in the performance of their proper function. You observe a candle is a very different thing from a lamp. With a lamp you take a little oil, fill your vessel, put in a little moss, or some cotton prepared by artificial means, and then light the top of the wick. When the flame runs down the cotton to the oil, it gets stopped, but it goes on burning in the part above. Now, I have no doubt you will ask, how is it that the oil, which will not burn of itself, gets up to the top of the cotton, where it will burn? We shall presently examine that; but there is a much more wonderful thing about the burning of a candle than this. You have here a solid substance with no vessel to contain it; and how is it that this solid substance can get up to the place where the flame is? Or, when it is made a fluid, then how is it that it keeps together? This is a wonderful thing about a candle.

You see, then, in the first instance, that a beautiful cup is formed. As the air comes to the candle, it moves upwards by the force of the current which the heat of the candle produces, and it so cools all the sides of the wax, tallow, or fuel as to keep the edge much cooler than the part within; the part within melts by the flame that runs down the wick as far as it can go before it is stopped, but the part on the outside does not melt. If I made a current in one direction, my cup would be lopsided, and the fluid would consequently run over--for the same force of gravity which holds worlds together, holds this fluid in a horizontal position. You see, therefore, that the cup is formed by this beautifully regular ascending current of air playing upon all sides, which keeps the exterior of the candle cool. No fuel would serve for a candle which has not the property of giving this cup, except such fuel as the Irish bogwood, where the material itself is like a sponge, and holds its own fuel.

You see now why you have such a bad result if you burn those beautiful fluted candles, which are irregular, intermittent in their shape, and cannot therefore have that nicely-formed edge to the cup which is the great beauty in a candle. I hope you will now see that the perfection of a process--that is, its utility--is the better point of beauty about it. It is not the best-looking thing, but the best-acting thing which is the most advantageous to us. This good-looking candle is a bad burning one. There will be a guttering round about it because of the irregularity of the stream of air and the badness of the cup which is formed thereby.

You may see some pretty examples of the action of the ascending current when you have a little gutter run down the side of a candle, making it thicker there than it is elsewhere. As the candle goes on burning, that keeps its place and forms a little pillar sticking up by the side, because, as it rises higher above the rest of the wax or fuel, the air gets better round it, and it is more cooled and better able to resist the action of the heat at a little distance. Now, the greatest mistakes and faults with regard to candles, as in many other things, often bring with them instruction which we should not receive if they had not occurred. You will always remember that whenever a result happens, especially if it be new, you should say: "What is the cause? Why does it occur?" And you will in the course of time find out the reason.