Part 6

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.

FOOTNOTES:

[5] Represented by the French word _hectare_.

CHAPTER THE EIGHTH.

THE SUN THE DEFINITIVE ABODE OF SOULS WHO HAVE ATTAINED THE HIGHEST RANK IN THE CELESTIAL HIERARCHY.--THE SUN THE FINAL AND COMMON DWELLING OF SOULS WHO HAVE COME FROM THE EARTH.--THE PHYSICAL CONSTITUTION OF THE SUN.--THE SUN IS A MASS OF BURNING GASES.

THE fundamental importance of the sun in the general economy of our world being finally established, our readers will not be surprised to hear that we assign that radiant and sublime abode to the human souls released from the earth, and successively purified and perfected by the long series of their multiplied incarnations in the bosom of the interplanetary spaces. Some philosophers have perceived this truth. The astronomer Bode placed the most elevated intelligences in the sun. "The happy creatures which inhabit this privileged abode," he says, "have no need of the alternate succession of day and night; a pure and unextinguishable light illumines it for ever. In the centre of the light of the sun, they enjoy perfect security, under the shelter of the wings of the Almighty."[6] Under what form may we picture to our fancy the inhabitants of the sun? We cannot answer this question without being acquainted with the _geography of the sun_, or as astronomers call it, his _physical constitution_, which differs essentially from that of the planets, of their satellites, and of the comets. He is unique in his position and office in the planetary system,--he must therefore be specially constituted. What is this special constitution? What is the geography of the sun?

Would that it were in our power to reply to this question with precision; would that we could describe the configuration of the sun. Unhappily, science has not yet reached that point. The problem of the sun's true nature is full of uncertainty. Astronomers are divided between two opposite theories, and that which seems to be the best supported, is too recent to be set forth in a dogmatic fashion. We can only summarize the actual condition of our knowledge on this question, explain the theory which seems conformable to ascertained facts, and applying it to the subject on which we are engaged, endeavour to deduce the physical condition, which, in our opinion, would belong to the inhabitants of the king-star.

Until the great epoch of the discovery of the telescope, at the beginning of the seventeenth century, in the time of Keppler and Galileo, only vague and arbitrary ideas respecting the sun prevailed. The educated, as well as the vulgar, beheld in it merely a globe of fire; the most learned declared that they found in it _pure fire, elementary fire, the principle of light, and of fire_. But as no means existed of examining the surface of the sun, and as his real distance from the earth was either unknown, or very imperfectly understood, a prudent reserve was maintained on this question. The discovery of the telescope immediately placed the astronomers in possession of the celestial realm; it enabled them to sound the depths of space, and to study the apparent configuration of the stars, including the sun himself. A few hours' observation with the astronomical spy-glass, and more was learned of the nature of the sun, than in the two thousand years of more or less philosophical reverie which preceded the discovery of the telescope.

With a glass which magnified the apparent diameter of the sun only twenty-sixfold, Galileo, repeating the observations of Fabricius, discovered the spots on the sun. Although Galileo did not use the smoked glasses which have since been found so useful, and although he limited his observations to the horizon, watching the great star at its rising and its setting, or when it was veiled by slight clouds, he studied its spots carefully, and described them faithfully.

We may observe that this discovery astonished the philosophers of that period, who were entirely submissive to the authority of Aristotle. The _incorruptibility of the sun_ was held in the schools as a sacred principle, according to Aristotle, and these unfortunate spots perplexed the philosophers. The peripatetics vied with each other in proving to the Florentine astronomer that the purity of the sun was an unassailable principle, and that the spots which he had perceived existed only on his eyes, or on the lens of his glasses.

But Galileo had seen correctly, and soon every one could convince himself of the reality of the phenomenon he had proclaimed. Not only do spots exist upon the disc of the sun, but they furnish the only means which we possess of becoming acquainted with the physical and astronomical peculiarities and properties of the great star. The examination of these spots led to the discovery that the sun revolves like the other planets, and that he accomplishes the entire revolution upon his axis in a period of twenty-five days. The sun's days are therefore twenty-five times as long as ours. Here, however, we must remark upon the word _day_. To us, the _day_ signifies the periodical return of the earth to the same point, after a complete revolution upon its axis, with an alternation of light and darkness. It is quite otherwise in the case of the sun, which, being self-luminous in all his parts, can never have any night.

We have said that the examination of the sun's spots established his rotation upon his axis. In fact, if we patiently observe the motion of a spot, or of a group of spots, we remark that it advances slowly from one edge of the solar disc to the other; for instance, if the point of departure be the eastern edge, the spot or group will advance with uniform speed towards the western edge, taking fourteen days to accomplish the distance. If we wait fourteen days more, we shall again perceive the same spot making its appearance on the eastern edge of the disc, the interval having been consumed in passing over the opposite and, of course, invisible side of the sun. The spot has therefore taken twenty-eight days to reappear, which twenty-eight days do not, however, represent the exact duration of the revolution of the sun himself. It must not be forgotten that the earth has not remained motionless during this long observation; she, too, has gone round in the sun, as the spots have done. This sort of advance, which causes us to see the same spot for a longer time than we should have seen it, if the earth remained motionless, is of three days' extent, the deduction of which from the twenty-eight given days, allows twenty-five days for the real duration of the sun's rotation upon his axis.