FOOTNOTES:
[4] On this subject see the book of Dupont de Nemours, "Philosophie de l'Univers," quoted by M. Pezzani in his "Pluralité des existences de l'âme," pp. 216-218.
CHAPTER THE SEVENTH.
PHYSICAL AND GEOGRAPHICAL POSITION OF THE SUN.
ACCORDING to our system of thought the sun is the central place in which souls which come from the ethereal spaces are finally gathered together. After having undergone the successive incarnations which we have described, souls, primitively human, finish by reaching the sun, by dwelling within the borders of the star-king.
This, then, is a fitting place for a description of the sun from the physical and astronomical point of view. Such a description will at once reveal the entirely sovereign part played by that globe which has no fellow. The astonishing attributes which belong to it, the unimaginable power which it wields, will sufficiently explain the place at the summit of the ascending scale of nature, which we assign to the sun.
In the first place, the sun is totally different from the other stars of our world. He resembles nothing, and nothing can be compared with him. Neither planets, satellites, asteroids, nor comets can give us any idea of him. His immense volume, his physical constitution, his exceptional properties place him in a totally separate rank, and afford full justification to those who claim for him a separate and sovereign place.
The enormous mass of the sun at once proclaims his supremacy. The sun is sufficiently vast to receive everything which could come to him from all the other planets. He surpasses in volume the united size of all the celestial bodies which revolve around him. He is six hundred times larger than the entire assemblage of the planets with their satellites, of the asteroids and the comets which compose what is called the solar world; that is to say, the world of which we form a part. The proportion in which the sun exceeds the earth in volume is, then, necessarily enormous; since he is larger than all the other stars put together. He is one million three hundred thousand times larger than our globe.
It is only by drawing that we can give an exact idea of the comparative sizes of the sun and the other planets. The reader will find in the accompanying illustration (Fig. 1) a figure which exactly represents the comparative dimensions of the sun, and the largest planets of our world. The earth, represented by a dot, gives an idea of what Mars, Mercury, and Venus, which are smaller than the earth, must be.
It takes three years to circumnavigate the earth. To circumnavigate the solar globe, under similar conditions, would take three hundred years. If human life be not more prolonged in the sun than on the earth, an existence would not suffice to enable a traveller to become acquainted with the surface of the globe he inhabits.
Fig. 1.—Comparative Dimensions of the Sun and the Planets.
Weight is thirty times more intense on the surface of the sun than on the earth. We know that a body which falls upon the earth traverses, in the first second of its fall, a space of four metres, nine centimetres. In the sun a falling body traverses 144 metres in the first second of its fall. It follows from this, that a human body, if transported to the sun, would weigh about 2000 kilogrammes, the weight of an elephant. The body of a dog or of a horse would weigh twenty-eight times as much as upon our earth, so that these animals would remain fixed to the surface. The conditions of nature must therefore be entirely different in the sun from what they are in the group of planets to which the earth belongs.
The sun sheds rays from perpetual fire, a characteristic that appertains to him alone among all the stars of our world. Of himself he burns, and sheds abroad light and heat. The other stars are neither warm nor luminous, and if the sun did not exist, they would be plunged into eternal darkness and eternal cold. This privilege alone ought to make us comprehend the immense importance of the central star.
The light and heat which emanate from the sun are constant; they are never interrupted, and they never lose their force. Thus, a second characteristic—constancy of illumination—separates the sun from all the other celestial bodies of our world.
The intensity of the real heat of the sun has been measured by the physicists. This result was attained in an endeavour to determine by experience the quantity of heat which accumulates in a given time, upon a certain portion of the earth's surface, exposed to the sun's rays, and adding to that element the quantities of heat which would be absorbed by the atmospheric air, the ethereal spaces, and the soil.
Pouillet, the French physicist, who undertook this critical investigation, arrived at certain results, which he states as follows:
"If the total quantity of heat emitted by the sun was exclusively employed to melt a layer of ice applied to the solar globe, and covering it completely in all its parts, that quantity of heat would be able to melt, in one minute, a layer of eleven metres, eighty centimetres, and in one day a layer of seventeen kilometres in thickness."
"'This same quantity of heat,' says Professor Tyndall, 'would boil 2900 milliards of cubical kilometres of water, at the temperature of ice.'"
The astronomer Herschel found, that, in order to extinguish the sun, to prevent his "giving out caloric," according to the scientific phrase, it would be necessary to dash a stream of iced water, or a cylindrical column of ice, eighteen leagues in diameter, against its surface, at a rate of speed of 70,000 leagues per second. A comparison adopted by Professor Tyndall gives us an amazing view of the intensity of the calorific force of the sun. "Imagine," says he, "that the sun is surrounded by a layer of peat, seven leagues in thickness, the heat produced by its combustion would be the same as that produced by the sun in one year." The physicists have measured the intensity of the sun's light with exactitude, as they had previously measured his heat.
It is known that the solar light is 300,000 times stronger than that of the full moon, and 765,000,000 stronger than that of Sirius, the most brilliant of the stars.
Bouguer discovered, by experiments made in 1725, that the sun, at a height of 31° above the horizon, gives a light equal to that of 11,664 candles, placed within 43 centimetres of the object to be lighted, and equal to 62,177 candles placed within one metre.
According to this result, if we take account of atmospheric absorption, and of the law of the variation of the intensity of light, which decreases in inverse ratio to the square of distance, the light given by the sun at its zenith would be 75,200 times greater than that of a single candle, placed within one metre. Wollaston had arrived at a similar conclusion. By means of experiments of another kind, made during the months of May and June, 1799, Wollaston found that 59,882 candles, at one metre, give as much light as the sun. Supposing the sun to be in the zenith, the lightening power of that great star would be equivalent to 68,009 candles.
There is but little difference between this valuation and that of Bouguer, who states the result at 75,200 candles.
Whatever may be the intensity of the light of the sun, we now possess other sources of light which approach to it. Such is the oxhydric light, produced by burning hydrogen gas by means of a current of oxygen gas, or air, a method of lighting which has recently been employed in Paris and in London. This light is equal in power to more than 200 candles. A thread of magnesium burning in the air, develops a prodigious quantity of light, which may be taken as equivalent to that of 500 candles. The electric light produced by a voltaic battery of from 60 to 80 coils, produces a luminous arc equal to the light of 800 or 1000 candles. In the latter instance the voltaic arc, according to Bouguer and Wollaston, would give 75 times less light than the sun, supposing the luminous electric point to be placed at a distance of one metre.
With very powerful batteries, it has been possible to go further, and produce a light not much inferior to that of the sun. Messieurs Fizeau and Foucault, by comparing the light of a voltaic arc, produced by the action of three series of Bunsen's coils, of forty-six couples each, with the light of the sun in a clear sky in April, have established that the light-giving power of the sun is not more than twice and a half that of the electric light.
The preceding numbers represent the light-giving power of the sun upon our globe, taking into account atmospheric absorption. Arago, on endeavouring to determine the intrinsic light-giving power of the sun, found that the intensity of the solar light is 52,000 times greater than that of a candle placed at one metre. But, according to more recent researches for which we are indebted to Mr. Edmond Becquerel, the result obtained by Arago is greatly inferior to the truth, and the light of the central star is 180,000 times greater than that of a candle placed at one metre.
All the planets, attended by their satellites, and all the comets which accidentally manifest themselves to us, turn round the sun. The sun remains motionless in the midst of this imposing procession of stars, which circulate around him, like so many courtiers paying him homage.
Thus, the sun is the heart of our planetary system; everything is drawn, everything converges towards him.
Half-informed persons will exclaim, "What can be more simple! The sun being six hundred times the size of all the other stars put together, the phenomenon of the condition of all those stars around the sun is explained by the law of attraction, which prescribes that bodies shall attract in proportion to their mass. If the sun attracts the stars of our world to itself, it is because his mass is greater than that of all the other stars collectively." But such an answer would be erroneous, involving the common error of taking a word for a thing, an hypothesis for an explanation, of putting a term of language in the place of a logical consideration. When Newton conceived the hypothesis (and the phrase) of reciprocal attraction of matter, he was careful to state that he only proposed to characterise by a name a phenomenon which in itself is entirely inexplicable, and of which we know nothing but the exterior mode of its manifestation, that is to say, the mathematical law. We know that bodies go towards each other in the ratio of their masses, and in the inverse ratio of the square of their distances; but why do they go towards each other? This is what we do not know, and what we probably never shall know. If, for the word attraction we were to substitute the word electrization, or, as Keppler did, the words affection, sympathy, obedience, &c., we should have a new hypothesis, with a new name, but the mathematical law would remain the same, the hypothesis only would be changed. The real cause which makes small bodies rush towards large ones, and the stars of lesser magnitude revolve round the stars of greater magnitude, is an impenetrable mystery to mankind.
Whatever may be the hypothesis by which we seek to explain the fact, it is certain that the sun holds the planets with their satellites, the asteroids and the comets, suspended above the abysses of space, and that they journey through the heavens in unintermitting obedience to his guiding influence. The sun draws with him all the stars which follow and surround him, like flatterers of his power, like humble slaves of his universal preponderance. Like the father of a family in the midst of his progeny, the sun peacefully governs the numerous children of sidereal creation. Obedient to the irresistible impulsion which emanates from the central star, the earth and the other planets circulate, roll, gravitate, around him, receiving light, heat and electricity from his beneficent rays, which are the first agents of life. The sun marks out for the planets their path through the heavens, and distributes to them their day and night, their seasons and their climate.
The sun is, then, the hand which holds the stars above the unfathomable abysses of infinite space, the centre from which they obtain heat, the torch which gives them light, and the source whence they derive the principle of life.
From all time the immense and unique task fulfilled by the sun in the economy of nature has been understood. But this great truth has only been deeply studied in our days. Science has gone far beyond all the imagination the poets had conceived relative to the preponderance of the sun in our world. By means of numerous experiments and abstruse calculations, modern physicists have proved that the sun is the first cause of almost all the phenomena which take place on our globe, and that, without the sun, the earth and no doubt all the other planets would be nothing but immense wastes, gigantic corpses, rolling about, frozen and useless, in the deserts of infinite space.
Professor Tyndall, who has added largely to the discoveries of physics and mechanics, has brought out this truth very strongly, and the results to which he has been led may be said to form the most brilliant page of contemporary physical science.
We shall now endeavour to explain how it is that everything on the earth, and no doubt on all the other planets also, is derived from the sun, so entirely, that we may affirm that vegetables, animals, man, in short, all living beings, are but the productions, the children of the sun; that they are, so to speak, woven out of solar rays.
In the first place, the sun is the primary cause of all those movements which we observe, in the air, in the water, or in the ground under our feet, and which keep up life, feeling, and activity on the surface of our globe.
Let us consider the winds, which have such important relations with all the physical phenomena of our globe. Whence proceed the winds? From the action of the sun. The sun heats the different portions of the earth very unequally, bestowing much more warmth on the tropical and equatorial regions than on the other latitudes, which he leaves exposed to cold. On each point of the earth which is struck by the rays of the sun, the layers of air near the ground are dilated and raised, and immediately replaced by colder layers from the temperate regions. Thus the periodical winds are produced. Across the hemispheres two great aërial currents are perpetually blowing, going from the equator to each of the poles; one, the upper current, towards the north-east in the northern hemisphere, and towards the south-east in the southern hemisphere; the other, the lower current, in a contrary direction.
The movement of the earth gives rise to other regular winds. The action of heat and of evaporation, added to the unequal distribution of the continents and the seas, produce others, which are irregular. Thus, for example, in the great valleys of the Alps, as in those of the Cordilleras, the warmth of the air regulates the afflux of the cold air of the mountains, and brings on tumultuous winds, and, in fact, hurricanes.
The sea breezes arise from the difference in the temperature of the shore during the day and the night. By day, the sun has warmed the shore and produced a considerable dilatation of the air. When the sun quits the horizon, this hot air is replaced by cool currents from the inland. The same phenomenon is reversed in the morning, when the sun returns; the shore is warmed, the hot air rises, and is replaced by the colder air of the sea, which then goes inland. Thus, the evening breeze comes from landward, and the morning breeze from seaward.
We see, therefore, that the great atmospheric movements which we call the winds, are due to the successive appearances and disappearances of the sun, as are also the lesser movements which we call breezes. The position of the sun, constantly varying according to the period of the year, and the hour of the day, explains the inequality and the continuous existence of the aërial current.
The general cause of the winds which preserve the homogeneity of the air in all the terrestrial regions, is the heat of the sun dilating the atmospheric air; its absence, on the other hand, causes that gaseous mass to contract.
The watering of the globe, that is to say the rain, an element indispensable to the exercise of life, is another consequence of solar heat. The waters of the seas, the rivers, and the lakes, those which steep the soil, or are exhaled from vegetable matter, are gradually transformed into vapour by the action of the sun's heat, and form clouds and invisible vapour. When the sun has quitted the horizon, these vapours grow cold in the bosom of the atmosphere in which they floated, and fall down upon the earth again in the form of dew, of fog, and of rain.
When the cooling of the watery vapour in the bosom of the atmosphere is more intense, instead of rain we have snow, that is to say, a fall of congealed water. It is chiefly on the summit of mountains that snow falls and accumulates, because the temperature of elevated places is always cold. In very great altitudes the snow, remaining for long periods on the tops of the mountains, passes into an intermediate condition, between snow and pure ice, and ends by forming those great expanses of congealed water which are called glaciers. During the hot seasons the glaciers melt by degrees; the water resulting from this melting process, flows down the slopes of the mountains into the valleys, and gives rise to springs, rivers, and streams. These streams and rivers run into the ocean, from which they are again evaporated by the action of solar heat, and reconstitute clouds and invisible vapour.
Thus is established and maintained that incessant circulation of the waters which lie on the surface of the earth, their continual exchange with the aërial masses, whose effect is to water the globe, a phenomenon necessary to the exercise of the functions of organized beings.
The regular currents which furrow the waters of the ocean are also the result of the action of solar heat. From the poles to the equator the waters of the sea are unequally heated, and this absence of equilibrium in the temperature of the sea occasions a regular furrow, or line from the poles to the equator, resulting from the displacement of the waters, the cold waves rushing in to replace the hot. The unequal evaporation caused by the unequal distribution of heat at the equator and the poles, concurs to produce a similar result, by augmenting the degree of saltness at the equator, without augmenting it at the poles, occasioning a certain difference in density, and finally displacement for want of equilibrium. The currents of the sea are thus entirely produced by the action of the sun.
We see, therefore, that the winds, the watering of the globe, and the currents of the sea are the consequence of solar heat.
The movement of the magnet is another physical result of the action of the sun, if it be true, as Ampère says, that the magnetic currents which traverse the terrestrial globe are nothing but thermo-electric currents engendered by the unequal distribution of heat on the surface of the globe.
In addition to being the agent of powerful physical forces, the sun is a valuable agent of chemical forces,—indeed, this is the greatest part which he plays in the phenomena of nature. The light and heat of the sun produce the most important chemical actions on the earth's surface; those on which the exercise of vegetable and animal functions depend. If the sun did not exist, life would be banished from the terrestrial globe. Life is the child of the sun, as I shall endeavour to prove to you.
The operations of photography serve to make us understand how it is that the sun presides over chemical action in the vegetable world. What is photography? What does that curious phenomenon which fixes a drawing formed by light upon a sheet of paper, consist of? A paper steeped in chloride or iodide of silver is placed in the focus of the lens of a dark camera, and the image formed by the lens is made to fall upon paper sprinkled with water. The portions of the picture not exposed to light produce no effect upon the salt of silver, which is incorporated with the paper, but the portions exposed to light decompose the salt of silver, and turn it black, or dark violet colour. On withdrawing this paper from the apparatus, where the operations have been carried on in darkness, we have a drawing which reproduces, in black, the luminous image formed by the lens. By certain means this image, solely produced by the chemical action of light, is rendered fixed and unalterable.
All the salts of silver thus exposed to light undergo an analogous decomposition. Nor are they the only salts which light modifies. Compounds of gold, platinum, and cobalt, properly prepared, may also be altered under the influence of direct or indirect rays, when exposed to the sun, or to his diffused light.
The light of the sun possesses the power of bringing about the combination of several other bodies. This is the case with hydrogen and chloric gas. If you mix equal parts of chloric gas and hydrogen in a bottle, and expose the mixture to the sun, an immediate combination will take place between the two gases, and chlorohydric acid gas will be formed. The combination will take place with so much force that it will be attended by a considerable escape of heat. If you throw the bottle containing the mixture up into the air, towards a space where the sun is shining, the bottle will break before it falls, with a violent explosion, at the moment of its contact with the light.
We might multiply examples of the chemical action produced by light only on substances belonging to the mineral kingdom, but it is sufficient for our purpose to say that the chemical action of light is still more powerful and more general in the vegetable than in the inorganic realm. This is a phenomenon of such importance that it is impossible to believe it otherwise than a premeditated design of nature.
One of the most fruitful discoveries of modern science is the recognition of the fact, that the respiration of plants depends upon the presence and the direct action of light, that is to say, that the decomposition of the carbonic acid which circulates in the tissue of vegetables, and which has been breathed up from the soil by the roots, takes place only when the plants are exposed to the sun. The labours of Priestley, Charles Bonnet, Ingenhouz and Sennebier, have taught us that the decomposition of carbolic acid into carbon, which remains fixed in the tissue of the plant, and into oxygen, which disengages itself from it, can take place only under the direct or indirect influence of the sun's rays. Our readers may easily convince themselves of this fact. Place a handful of green leaves in a glass full of water, and expose the glass to the sun. At the close of the day the upper portion of the glass will be filled with gas, which is nothing but pure oxygen, the result of the breathing of the leaves.
All the importance, all the value of such a phenomenon will be evident, if we reflect that it takes place over the whole extent of the globe, and that the respiration, which means the life of all the vegetable masses which cover the earth, depends solely upon the light of the sun. It is by means of the respiration of the plants, which restores oxygen to the atmospheric air, that nature makes up for the withdrawal of oxygen by the respiration of animals, by the continual absorption of that gas by numerous mineral substances, and by the frequent combustions, natural and artificial, which occur in the world. The result of these combustions would be the disappearance of the greater portion of the oxygen contained in the air, if there did not exist a permanent machinery for the restitution of that oxygen. This permanent machinery is the respiration of plants, produced by solar light. So absolute is the dependence of plants for their respiration on the action of the sun's light, that if it be intercepted by clouds, the escape of oxygen from them suffers a marked diminution. If the light of the sun be suddenly stopped, which occurs during a total solar eclipse, the escape of oxygen ceases, and the plants transpire carbonic acid only, as they always do during the night.
It is for this reason that a plant kept in complete darkness loses its colour, and becomes white. It does not respire, it emits carbonic acid gas without retaining carbon, it becomes etiolated, according to the scientific phrase, which means that the plant no longer lives at the cost of the external air, or of gas furnished by the soil, but consumes its own substance. The whitened salads which we prefer are not green only because they are grown in darkness, and the mushrooms brought to table are white only because they are reared in cellars.
M. Boussingault, who has studied vegetation in darkness, finds that the leaves of a vegetable which has never had any light at all, in its first appearance and development, never exhales oxygen, its respiration furnishes carbonic acid gas only. The plant, therefore, breathes just as an animal does. We must observe in this case that the substance of the seed only supplies this product. The plant borrows nothing from without, consumes nothing but the elements which were contained in the seeds, and dies when those nutritive elements are exhausted. The duration of its existence depends entirely on the weight of the seed whence it has sprung. If a well-developed plant be kept in darkness, the same fact may be observed. The plant gives out nothing but carbonic acid, and, as it borrows nothing from without, it perishes when it has thus devoured its own substance. M. Sachs says, in his Physiologie Végétale, that the movements proper to the leaves of many vegetables cannot take place if the plant is kept in darkness. Plants so kept remain always in the condition which Linnæus defined as sleep. Flowers contained in natural coverings, which in a great measure debar them from the light of the sun, do indeed produce colours, but those flowers are formed inside their natural coverings, at the expense of substances contained in their leaves, which could not be produced except under the influence of light. The same truth applies to fruits.
Leaves, flowers, fruits, are then, as the German physiologist, Moleschott, has said, "beings woven of air by light." The same author adds: "When we contemplate the brilliant colours of the flowers, and when their delicious perfume gives serene satisfaction to that poetic faculty which exists, though it may slumber deeply, in the soul of every man it is still the light which is the mother of colour and of perfume."
The influence of the sun on vegetation is of fundamental importance. Without the sun no plant would grow upon our globe. In those regions which are permanently deprived of the powerful and beneficent torch of nature, towards the extreme north, all vegetation is stunted, and higher still, it does not exist. Absence of light, and cold, are the causes of the complete disappearance of the natural adornment, and the useful tribute, which elsewhere vegetation furnishes to the earth. In the hot regions, vegetation is vigorous and extensive, in proportion to the abundance of sunshine poured upon them. There is nothing to be compared to the luxuriant vegetation of the tropical countries in both hemispheres. The vegetation of Brazil, of equatorial Africa, and the inter-tropical regions of India, is renowned for its abundance and variety.
Agriculture, enlightened by modern chemistry, has brought to light the special importance of the sun in promoting the activity of vegetation, and producing combinations of substances not to be attained by any action except that of the sun. M. Georges Ville, a professor at the Museum of Natural History in Paris, states, as the result of numerous experiments, that the activity imparted to vegetable production by the sun is truly miraculous. No chemical fact, no theory, according to the learned professor, can explain the mystery of solar influence, and its prodigious power over the development and produce of vegetables.
Let us remark, before we leave this subject, that by a providential circumstance the present generations of mankind are profiting by the chemical force of the sun which nature has stored in her great vegetable depôts for thousands of centuries. For instance, what is coal, which feeds all our industries, supplies our steam machines, ships, engines, and locomotives? It is the residue of those gigantic forests which covered the earth during the geological periods. The substance of the trees of the forests of the ancient world was at first changed into peat, which, becoming more and more compact by the action of ages, was finally pressed into the hard and heavy body which we call coal. But what was the cause, what was the first agent, which produced the trees of those forests, in the antediluvian times? It was the chemical force of the sun. This force, or, if the term be preferred, the products of the chemical force of the sun, have been accumulated and preserved in the wood, and then in the coal which that wood has become. We find it thus, and we use it, to our present profit.
Thus, the glowing sunshine which lighted and warmed the ancient world, is not lost to us. Contemporary generations inherit those very rays, and that same chemical force. The power of the sun, which has slumbered in the coal for millions of years, arouses itself for us, comes forth into the day, and transforms itself in our hands into a mechanical agent.
The light and heat of the sun, which play so great a part in the vegetable kingdom, exercise influence of a similar kind over the animal kingdom. If we reflect that plants are indispensable to the food of the majority of animals, that the creation of vegetables necessarily preceded that of terrestrial animals (since vegetables constitute their food), and that animals must inevitably disappear from the earth if plants ceased to exist; we shall be led to acknowledge that animals originate as certainly, though indirectly, from the force of the sun as the plants themselves.
Besides, it can be proved that the action of the sun is directly indispensable to the maintenance of animal life. In the first place, is it not the fact that solar light and heat exercise an immense influence on the health of animals and of man? To convince ourselves of that, we need only compare men who pass the greater part of their lives in the air and sunshine, with men who live in dark houses, in the narrow streets and lanes of great cities. Not only are these dwellings unwholesome because they are damp, but they are fatal to health because they are not enlivened by the presence of the sun.
Light, altogether indispensable to the exercise of respiration in plants, is not indispensable in the same degree to the respiration of animals. It is, however, certain that the products of the respiration of man and animals are less abundant by night than by day. Moleschott has found that the quantity of carbonic acid gas exhaled by an animal is augmented by the intensity of the light of day, and is at its minimum in complete darkness; "which amounts to this," adds that author, "that the light of the sun accelerates molecular action in animals."
Thus, the rays of the sun are a primary condition of the existence of animals, because they produce the formation of plants, the essential basis of the alimentation of animals and of man, and because they preside over the fulfilment of many of their physiological functions. We find views of precisely the same order as those we have endeavoured to express, eloquently put forward in Professor Tyndall's work on "Heat:"
"And as surely as the force which moves a clock's hands is derived from the arm which winds up the clock, so surely is all terrestrial power drawn from the sun. Leaving out of account the eruptions of volcanoes and the ebb and flow of the tides, every mechanical action on the earth's surface, every manifestation of power, organic and inorganic, vital and physical, is produced by the sun. His warmth keeps the sea liquid, and the atmosphere a gas, and all the storms which agitate both are blown by the mechanical force of the sun. He lifts the rivers and the glaciers up the mountains; and thus the cataract and the avalanche shoot with an energy derived immediately from him. Thunder and lightning are also his transmuted strength. Every fire that burns and every flame that glows dispenses light and heat which originally belonged to the sun. In these days, unhappily, the news of battle is familiar to us, but every shock and every change, is only an application or misapplication of the mechanical force of the sun. * * * * The sun comes to us as heat; he quits us as heat; and between his entrance and departure the multiform powers of our globe appear. They are all special forms of solar power; the moulds into which his strength is temporarily poured, in passing from its source through infinitude."—p. 431.
The mechanical force which the heat of the sun represents has been calculated, and the numbers thus ascertained are curious. In order to understand how a heat agent can be expressed by figures of mechanical force, we must have a general idea of that theory which constitutes the most valuable creation of natural philosophy in our day; we allude to the mechanical theory of heat, or the doctrine of the mutual transformation of physical forces.
Experience has proved that heat changes, under our eyes, into a mechanical force. See how, by the action of the steam engine, watery vapour becomes cold, and the dispersed heat immediately produces a mechanical force, and you will understand how it is that we maintain that heat transforms itself into force. This being admitted, it is easily explicable that one of those elements may be represented by the others, or that at least we may represent the value of both force and heat by a common unit. This common unit is called a calorie, and expresses the quantity of heat requisite to raise the temperature of a kilogram of water one degree. On the other hand, the term kilogrammeter is used to express the quantity of force requisite to raise a kilogram to the height of one yard (métre) in a second.
Physicists have succeeded in solving the difficult problem, which consists of ascertaining how many kilogrammeters may be produced by a calorie, transformed into mechanical labour. The works of Mayer, Joule, Helmholtz, Hirn, Regnault, &c., establish that a calorie is equivalent to 425 kilogrammeters, that is to say that the quantity of heat requisite to raise the temperature of a kilogram of water to 1 degree centigrade produces a mechanical action represented by the elevation of a weight of 425 kilograms 1 yard (métre) in height in the space of a sound. 425 kilograms are called the mechanical equivalent of heat.
With this information at our service, we are enabled to calculate in units of mechanical force the work done by solar heat, by transforming itself into mechanical force. And, if we calculate the total heat of the sun diffused over the earth, during a given time, we can calculate the sum of the forces which all this distributed heat would develop on the surface of the earth, if it were all employed in mechanical labour. In one year every square yard of the surface of the earth receives 2,318,157 calories, that is to say, more than 23,000,000,000,000 of calories to each space of 2 acres, 1 rood, 35 perches.[5]
To understand the intensity of this force, we must conceive a steam engine, which, instead of working at 200 or 300 horse-power, like the engines of our larger steamers, should work at 4,163 horse-power. And this, we must bear in mind, refers only to the small space above mentioned. If we calculate the entire surface of the earth, we arrive at the astounding total of 217,316,000,000,000 horse-power. In order to conceive such a force, we must picture to ourselves 543,000,000,000,000 steam engines each working without relaxation day and night, at 400 horse-power. That is the amount of work which the heat of the sun does for our globe alone.
The physical and mechanical actions which take place on our planet, vegetation, the phenomena of animal life, industrial and agricultural operations absorb only a very small quantity of this enormous mass of forces. Professor Tyndall says on this subject, in the book we have already quoted:—
"Look at the integrated energy of our world—the stored power of our coal-fields; our winds and rivers; our fleets, armies, and guns. What are they? they are all generated by a portion of the sun's energy which does not amount to 1/2300000000th of the whole. This, in fact, is the entire fraction of the sun's force intercepted by the earth, and in reality we convert but a small fraction of this fraction into mechanical energy. Multiplying all our powers by millions of millions, we do not reach the sun's expenditure."—p. 433.
In this chapter we have analyzed the different physical and vital effects produced upon our globe by the light and heat given out by the sun. We have considered its action upon animate and inanimate nature. We have seen that the sun is really the great cause of physical action on our globe, and that he is also the first principle of both vegetable and animal life. Without the sun life would be banished from the terrestrial globe; as we have already said, life is the offspring of the sun.
We know that in speech, heat and life are almost synonymous words. In every language we find it said that persons are frozen by death, in the icy sleep of death, that cold is death-like, &c. This image is an exact expression of the reality. An animal or a plant, when deprived of life is necessarily cold. A shiver is the precursor of every malady, and the sure forerunner of death. Every dead body is a cold body. It may be said that in the animal form cold takes the place of life, as in inanimate bodies cold succeeds to heat. Let us now consider the following facts. It is solely by the prolonged action of heat that plants can germinate, grow, and develop themselves; in order to come to perfection, every plant requires an ascertained number of degrees of heat, and botanists and agriculturists know quite accurately the total number of degrees of heat requisite to ripen their cereals, and make their fruit-trees bear. A prolonged and undisturbed accumulation of heat is indispensable to produce life in the impregnated egg of a bird, so that by employing caloric in a hatching machine, the process of hatching may be artificially perfected. The eggs of viviparous animals are sustained by the heat of the mother's body, and besides, as Hervey says, everything that has life proceeds from an egg (omne vivum ex ovo). If we recall to mind that, after the development of the germ in mammiferous animals, the unvarying maternal heat is indispensable to the formation of the organs of the fœtus, we shall be led to inquire whether heat does not directly produce life, whether heat does not transform itself into vital force. Modern philosophers who have propounded the Mechanical Theory of Heat, that is to say the profound and admirable doctrine of the mutual conversion of forces, the professors who have proved by mathematical evidence that heat converts itself into mechanical force, and the converse, might perhaps complete their brilliant synthesis by adding that heat, which converts itself into mechanical force, can also transform itself into life, or into vital force, and that the splendid theory of the transformation of forces does not apply to inanimate bodies only, but finds an astonishing confirmation in animate bodies.
Thus heat and life would be the manifestation of one and the same power, and the cause of life would be found to dwell, like the cause of mechanical force, in the sun.
