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From all the considerations, all the facts which we have just advanced, we conclude that the sensibility of plants is not to be contested, since no one can think of denying that privilege to certain zoophytes which can with difficulty be distinguished from vegetables.

We see an imposing tree, a stately oak with sturdy branches, growing on the sea coast. Not far off, on the sand of the shore, lies a star-fish flung there by the waves. A few yards below, on the surface of the water, floats a sponge, a branch of coral, a madrepore. When the icy wind blows, when the hurricane lifts the angry waves, which is it, the animal or the plant that will manifest sensibility to the tempest? The sponge, the coral, the madrepore will remain as indifferent to the fury of the elements as the rock in which they are incrusted, or as the pebble on which the star-fish stretches out its four motionless arms. But, the majestic oak will shudder at every gust of the tempest; he will bend his branches and shut up his leaves to shelter himself from the icy blast or the furious storm; and a mere glance at his attitude will indicate to you that an abnormal perturbation reigns in the atmosphere. Would you seriously say, in that case, that the vegetable feels nothing, and that the animal is sensible? Would you not, on the contrary, be inclined to declare that the tree is the sentient being, and that the star-fish, the sponge, the madrepore, are the creatures which are destitute of feeling?

Pause beside still water and seek for the polype or fresh-water hydra which we have just mentioned. You will find it difficult to disentangle this zoophyte from the reeds and willows which surround it. You will find, at length, a kind of membranous tube, a few centimetres in length. Is that the polype you were looking for? Is it not rather the stubble of some reed or grass plant? This living twig, with nothing to distinguish it in appearance from a herbaceous plant, is constantly fixed in the same place, like an aquatic vegetable. It makes some faint movements, consisting simply of the opening and shutting of the orifice of the tube, which solely constitutes its being. Sometimes it lengthens, sometimes it contracts itself, by stretching out membranous arms, as fine as threads, by means of which it seizes and drags towards it the water insects which chance to pass near it. This is the one single characteristic of its animality. At this rate, an aërial plant, the fly-catcher, would be just as much an animal as our polype, since it catches the insects which venture to crawl upon its leaves.

At the bottom of the sea there is a very curious zoophyte, the actinium, or sea-anemone. For a long time this creature was confounded with the plants, and held to be an ocean flower. Those who admire the beautiful, bright-coloured actinia, in the Garden of Acclimatization, in Paris, who look at them, waving on their flexible stem, shaking the coloured appendages and fringes which adorn their heads, find it hard to regard these charming queens of the waters otherwise than as real flowers. And, in fact, for ages, the sea-anemones were held to be marine plants.

In the last century, coral was held to be a marine shrub, and it was even believed that the flowers of the coral had been discovered. An academician of Paris, Count de Marsigli, created a European reputation for himself by this supposed discovery. Peyssonnel, a Provençal naturalist, found the utmost difficulty in opposing this idea, and in establishing the fact that these supposed flowers of the coral were in reality young corals. He had the whole Academy of Sciences against him; and his opposition to the ideas of the Academy brought him into such disgrace, that he was obliged to leave France and to go to the Antilles, where he died in obscurity as a doctor of medicine. And all this because he maintained that coral is not a plant, and does not produce flowers!

The famous Genevese naturalist, Charles Bonnet, anticipating the knowledge of our day by more than a century, has given a most interesting form to the parallel between animals and plants, in his work entitled Contemplation de la Nature. We cannot resist the pleasure of quoting the following passage, in which Charles Bonnet shows in a striking manner what are the difficulties in the way of distinguishing the plant from the animal, and how those difficulties are disposed of by those who dispute the sensibility of plants:—

"Everything is graduated in nature," says Charles Bonnet, "and, in refusing to admit that plants are sentient, we force nature to make a jump without any assignable reason.

"We observe that feeling decreases by degrees from man to the nettle, and to the mussel, and we persuade ourselves that it stops there, because we regard these animals as the least perfect. But there are, perhaps, many degrees between the feeling of the mole and of the plant. There are, perhaps, still more between the most and the least sensible of the plants. The gradations, which we observe, ought to persuade us to this philosophy; the new beauty which it adds to the system of the world, and the pleasure to be derived from the multiplication of sentient creatures ought to contribute to induce us to admit it. I willingly admit that this philosophy is much to my taste. I love to think that those flowers which adorn our fields and our gardens with a brightness constantly renewed, those fruit trees which are so pleasant to our eyes and our palate; those majestic trees that compose the vast forests, which time seems to have respected, are so many sentient creatures partaking after their fashion in the sweetness of existence.

"Plants offer some facts to our observation which seem to indicate that they possess feeling, but we are not likely to perceive those facts, because of the strong persuasion that they are insensible, which has prevailed among us for so long. We ought to agree to consider the question tabula rasa, and to subject plants to a new, impartial, and unprejudiced examination. An inhabitant of the moon, possessed of intellectual faculties like ours, but without any preconceived ideas about the insensibility of plants, would be the philosopher whom we require. Let us imagine such an observer engaged in studying the productions of our earth, and, after having given his attention to the polypes and other insects multiplied by the process of grafting, passing on to the contemplation of vegetables. He would, doubtless, take them at the period of their birth. With this view, he would sow seed of various species, and he would carefully watch their germination. Let us suppose that some of those seeds have been reversed in the sowing, the sprouting part turned downwards, the stem upwards; and the observer has the skill to distinguish one end of the seed from the other, and knows their functions. After some days, he will remark that the seed has grown into this reversed position, that the stem is turned upward, and the sprouting portion downward. He will feel no surprise; he will attribute a circumstance which is so hurtful to the life of the plant, to the mistake he has made in sowing the seed. But, continuing to observe, he will see the sprout and the stem each bending itself in the opposite direction, and trying to attain the right position. This change of direction will strike him as very remarkable, and he will begin to suspect that the organized being which he is studying is endowed with a certain amount of discernment. Too prudent, however, to pronounce upon these early indications, he will suspend his judgment and pursue his investigations. The plants whose germination our physicist has been observing, have been raised in the neighbourhood of a hedge. Thus favoured, and carefully cultivated, they have made great progress in a very short time. The soil which surrounds them at some distance is of two opposite qualities. That on the right of the plants is rich, damp, and spongy; that on the left is dry, hard, and gravelly. Our observer remarks that the roots, after having begun by extending equally on both sides, have changed their direction, and have spread out towards the rich and humid soil; over which they are stretching, and thus threatening to deprive the plants already there of their due share of nourishment. To prevent this inconvenience, he digs a ditch between the plants which he is observing and those they threaten to starve, and now he thinks he has provided against everything. But the plants, which he believes he has governed, disconcert all his precautions by extending their roots downwards, under the ditch, and gaining the other side.

"Surprised at this, he uncovers one of these roots, but without exposing it to heat, and holds a sponge steeped in water towards it. The root turns itself to the sponge, and when he changes its position, the root accommodates itself to each alteration.

"While our philosopher is meditating profoundly upon these facts, other facts equally remarkable present themselves almost simultaneously. He observes that all these plants have leaned away from the hedge, and are bending forward as though to present every portion of their bodies to the beneficent smiles of the sun. He sees that all the leaves are so turned that their upper surface is exposed to the sun, or to the fresh air, and that the lower surface is directed towards the hedge, or the ground. Former experience will have taught him that the upper surface of leaves serves chiefly as a defence for the lower surface, and that the latter is principally destined to pump up the moisture rising from the earth, and provide for the evacuation of what is superfluous. The direction of the leaves which he notices appears quite in harmony with his experiences. He studies this portion of the plant with increased attention.

"He remarks that the leaves of some species seem to follow the movements of the sun, so that in the morning they turn to the east, in the evening to the west. He sees that some leaves close themselves against the sun, others against the dew. He observes an analogous movement in certain flowers. Afterwards, he observes that no matter what the direction of the plants relative to the horizon has been, the direction of the leaves is always that which he has at first noticed, he bethinks him of changing this direction, and of placing the leaves in a position exactly contrary to their natural one. He has already had recourse to similar means in order to assure himself of the instinct of animals, and to ascertain its bearings. With this view he bends perpendicular plants towards the horizon, and keeps them in that position. Thus, the direction of the leaves is absolutely changed; the upper surface, which previously turned to the sun or to the fresh air, now looks towards the earth or the interior of the plant, and the lower surface, which formerly looked towards the earth or the interior of the plant, now turns to the sun, or the fresh air. But very soon all these leaves begin to move, they turn on their stem as on a pivot, and in an hour they will have resumed their former position. Our observer, wishing to assure himself whether leaves and branches when detached and plunged into water will preserve the inclinations which they manifest when upon the plant of which they formed a portion, subjects them to an experiment whose results leave him no doubt of the fact.

"He places wet sponges under the leaves, and he sees the leaves turn towards the sponges and endeavour to adhere to them by their lower surfaces. He also observes that certain plants, which he has shut up in his cabinet and in a cellar, have turned towards the window, or the grating respectively.

"Finally, the phenomena of the Sensitive Plant, its varied movements, the promptitude with which it contracts when touched, form the interesting subject which terminates his researches.

"Thus plentifully supplied with facts which all seem to tend to the support of belief in the sensibility of plants, which side will our philosopher take? Will he surrender to these proofs? Will he suspend his judgment? I think he will take the first part."¹⁶

Charles Bonnet believes, in short, that the plant, as well as the animal, is endowed with sensibility.

According to the system which we have developed, the animal is possessed of a soul, which is still very imperfect, and endowed only with faculties corresponding to its needs. But, since the animal, in addition to the sensibility enjoyed by the plant, possesses intelligence also, we must conclude from thence that the plant has not a soul, properly so called, but only the rudiment, the commencement, in other words, the germ of a soul.

We know that the sun has the privilege of giving birth to organic life upon our globe, his rays have power to produce the formation of living tissues, plants or zoophytes, when they fall upon the earth or the waters, and we may draw this conclusion from all that has gone before, that the sun sends down upon the earth animated germs under the form of his rays, which emanate from the spiritualized creatures who dwell in the king-star.

Thus our system of nature completes itself; thus, thanks to solar radiation, the two ends of the immense chain of organized beings whose place and part in the vast theatre of the worlds we have attempted to define are united. Life begins in the waters, its first appearance is in plants and zoophytes; for these two classes of living creatures obey the same laws, and appear to have the same origin. The sun, by sending his vivifying rays upon the earth, produces the formation of plants and zoophytes, which are the points of departure of organization. The animated germ deposited by the sun in plants and zoophytes grows, passes from the zoophyte to the mollusc, or articulated animal, and then undergoes a further development, by passing from the mollusc or articulated animal to the fish. This germ of a soul thus becomes a rudimentary soul, provided with certain faculties. In the zoophyte and the mollusc it had only sensibility; in the fish, and then in the reptile, and the bird, it has attention and judgment. The faculties are augmented in proportion as the animal mounts higher in the organic scale. Arrived at its summit, the human being, the soul is in possession of all its faculties, and especially of memory, which during the animal stages of the ascent is obscure and uncertain.

To accord sensibility to plants permits us to unite all the creatures of the living creation, and thus to complete our general system of terrestrial nature.

CHAPTER THE THIRTEENTH

DOES MAN EXIST ELSEWHERE THAN ON THE EARTH?—DESCRIPTION OF THE PLANETS.—PLURALITY OF INHABITED WORLDS

THROUGHOUT the preceding chapters we have reasoned as if the earth were the whole universe. Indeed, almost all men believed that such was the case, from the first establishment of society until the last century. Great mathematical knowledge, profound study, and highly perfected optical instruments are requisite to rectify the false ideas, the errors, and the illusions which are the result of a simple view of the earth and the sky. Great efforts of the mind, and a very difficult struggle against the testimony of our senses are necessary to the recognition that the earth moves, and that the sun is motionless. In order to distinguish the place and the office of each of those softly beaming globes, in the midst of the uniformity of aspect presented by the stars which shine during the night, patient and severe observations, transmitted and repeated from age are indispensable, and, in addition, an excellent scientific method. Let us therefore not be surprised that men have taken so much time to comprehend the ordering of the universe, and that they had only the most childish conception of them for thousands of years. The ancients, the Greeks, the Romans, the Egyptians, knew nothing of the universe, except the earth (nor did the Orientals, with the exception of some truly learned men, who had divined the general mechanism of the universe by methods unknown to us, but they concealed their knowledge from the profane). These ancients could speak of only a small portion of the globe: of Europe, Asia, and the North of Africa. The remainder was a dead letter for the peoples of antiquity. After them, and following their example, the first Christians reduced the universe to what they knew of it; they believed there was but one world, because they saw only one. The earth was for them the universe. In the stars they saw only brilliant spots, like silver nails in the celestial vault, to enhance the azure, and charm the eyes of men in the quiet of the night. The moon was the natural beacon of the earth. In the sky there was a shining track followed by the sun, and the torch of day was no larger than the beacon of night. The celestial region which spread itself above the sun and the moon was the Empyrean of the ancients, the Paradise of the Christians and the Mussulmans. It was at once the sojourn of clouds and of light, the habitation of the elect of God, of the saints and the just. Under the earth, and in its interior, were immense abysses, gulfs, and cavities, the dark dwellings of the damned.

This simple cosmogony, which merely translates what our eyes show us, has been that believed by every people in their infancy. Among the savage tribes of the two worlds, in America and in Africa, as in the ancient East, among the Romans as among the Egyptians and the ancient Greeks, this coarse simplicity and absolute ignorance of the constitution of the world prevailed. On this profoundly false basis all the ancient religions were founded. The social customs of modern peoples are based upon the same errors. Language has consecrated them; the earth is everywhere called the world, as the ancients called it (mundus, κόσμος); every one says the sun travels, or goes, from east to west, and that the stars rise and set.

Poetry has set its eternal seal on this vicious system, and has, so to speak, consecrated it, by clothing it with all the prestige of genius and imagination.

Modern astronomy has caused the false skies of antiquity to vanish away; it has dispersed the pretensions of the celestial vault, sown with brilliant spots, and substituted a simple mass of coloured air. It has revealed the true office of each of those stars which we see by day or by night. It has fixed, in an indisputable manner, the real place of the earth in the universe, and, to say the truth, that place is singularly small.

We know now, that the earth, far from being herself the world, is only an imperceptible point of the world. If we only compare it with the sun, we know that our globe is one million three hundred thousand times smaller than the sun. This takes us far away from the idea of the ancient Greeks, who thought they ventured much in asserting that the sun was as big as the Peloponnesus.

In addition, the earth has been dispossessed of all privileges. It was believed formerly to be unique and unrivalled, we now know that there are an infinity of other globes similar to the earth, so that she is no more than one individual in a group of other individuals who resemble her. We know that the earth figures among the planets, that she is only a planet of our system.

What, then, is a planet? the reader will ask. An attentive gaze directed to the stars of night will make him understand it. Let him examine, on any fine evening, the star which is pointed out to him as Mars or Jupiter, and to which a certain position is assigned at a given hour. Then, a few hours later, let him come and look once more for Mars or Jupiter, and he will perceive that the position of Mars or Jupiter, with respect to the other stars, is changed. Or he may do better still. Let him look at Mars or Jupiter through the telescope of an observatory, or the glass of one of those open-air astronomers who are to be found in the public ways in Paris and other great cities. Thus he may see Mars or Jupiter change his place under his own eyes. While the other stars remain motionless, Jupiter or Mars will pass away from the field of the glass.

There are, then, fixed stars and movable stars. The movable stars are the planets (πλανήτης, from πλάνος, wandering). The fixed stars are what we call stars. It is not difficult to distinguish the planets from the stars with the naked eye. The stars emit sparkling light, whence comes their name, from the Latin stellare, to shine, and their light twinkles. The planets, on the contrary, shine with a steady, mild, unvacillating light. The reason of this difference is, that the light shed by the stars is their own. The stars are so many suns resembling ours. They illumine worlds like our world, so prodigiously distant that we cannot even perceive them. The planets do not shine of themselves; they merely reflect, like gigantic mirrors, the light of the sun which illumines them, and renders them visible to us. Thus, the planets are stars which travel. They revolve around the sun. The earth, being a planet, is a travelling star, which revolves around the sun.

But the earth is not the only planet of our solar system. There are seven others, which do not differ essentially from the earth. The names of the eight planets which compose our solar system, are as follows, arranged according to their distance from the sun: Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Between Mars and Jupiter there is a collection of small bodies, which seem to be fragments of broken planets; they are called asteroïds. At present, in 1871, more than a hundred are known, and it is not yet fifty years since they were first sought for in the sky. These asteroïds may be collected together in our fancy, and formed into a separate group, which would be a ninth planet. Let us glance at the planets which compose our solar system.

Plates 4 and 5, which accompany these pages, will suffice to give an idea of the relative dimensions of the planets. In these two plates the planets are arranged according to the order of their distance from the sun. In plate 4, Mercury, Venus, the Earth, and Mars are represented; in plate 5, the asteroïds Jupiter, Saturn, Uranus, and Neptune. Mercury is the nearest planet to the sun, his distance from the central orb being only fourteen millions of leagues, which, in astronomy, is near neighbourhood. This planet revolves upon its axis with the same rapidity as the earth. The day, in Mercury, is only three minutes longer than ours (24h. 3ms.). Being closer to the sun than the earth is, Mercury turns more quickly round the sun, so that its year is only 88 days, whereas ours is 365 days.

We know that the sole cause of the inequality of the seasons, as well as of day and night in the planets, is the inclination of the star on its axis of rotation. If the planets, while revolving round the sun, retained the verticality of the axis which joins these north and south poles, there would be perfect equality in the distribution of the solar light and heat over the same latitudes; along each parallel there would be a complete regularity in the lighting and warming of the planet; the differences of heat and cold would not depend on anything but their greater or less distance from the sun. But this verticality only exists for two or three planets of our system. The others, and among them Mercury, Venus, the Earth, and Mars, are strongly inclined on their axis of rotation.

They revolve in a bent position, as if they had received a great blow on the shoulder, which had caused them to deviate from their primitive and regular situation. From this there results a very variable disposition of the duration of the light, and consequently of the heat, which these inclined planets receive from the horizontal rays of the solar star. Thus the inequality in the length of the days and nights, and the diversity of the four seasons on the same parallel, are accounted for.¹⁷

Mercury. Venus. Earth. Mars. Sun.

Fig. 4.—Comparative Size of the Planets Mercury, Venus, the Earth, and Mars.

The inclination of the axis of the terrestrial sphere is 23° which is a considerable deviation, and occasions great differences in the duration of days and of seasons on different points of our globe. The inclination of the axis of the planet Mercury is enormous: it is 70°. This planet bends over itself as if about to fall. Hence results prodigious variation of light and heat on the same parallel, and seasons whose abrupt changes must be painful and hard to bear by the inhabitants of this planet, if such inhabitants exist.

Mercury is five times less than the Earth, as is shown in plate 4. Venus comes after Mercury, according to distance from the Sun.

Venus, which is 27,000,000 of leagues from the Sun, receives twice as much light and heat as our globe. Its days are of nearly the same length as ours (23 hours, 21 minutes), but its year, necessarily shorter than that of the Earth, since it is nearer to the Sun, lasts only 224 days. Its seasons last two months each. Its globe is nearly of the same bulk as that of the Earth. Venus is almost always wrapped in clouds, which must fall in rain, forming rivers and seas. These waters refresh the plains, which must be scorched by the heat of the burning sun. The seasons are still shorter and more unequal in Venus than in Mercury; its axis is, in fact, inclined at 75°.

After Venus comes the Earth, which is almost of the same bulk, but 28,000,000 of leagues from the Sun. Its diameter is nearly 3000 leagues. It accomplishes its revolution on its axis in 24 hours (23 hours, 56 minutes, 4 seconds), and in 365 days, 5 hours its revolution around the sun.

The inclination of the Earth's axis is 23°, which produces the differences of days and nights, and the inequality of the seasons, according to latitude. The Earth possesses a privilege denied to the planets Mercury, Venus, and Mars; she has a secondary star, or satellite, called the Moon. Placed at a distance of only 90,000 leagues from the Earth, the Moon accomplishes her revolution around it in 27 days. It is not the object of this work to give any description of our globe. We will suppose our readers to be sufficiently acquainted with it, and pass on to the planet which comes next to it in the scale of distance from the Sun. This is the planet Mars.

An extraordinary resemblance exists between Mars and the Earth. Physical, geographical, and climatological conditions, days and nights, seasons, celestial perspectives, all are alike in these two planets, with the sole difference that the globe of Mars is half as small again as that of the Earth; so that, if a man were transported to Mars, he might believe himself to be, not in a strange planet, but in a little known corner of the Earth, such as Australia or Polynesia.

As we pursue our journey through the heavens, ever increasing our distance from the Sun, we shall find, after Mars, the group of the Asteroïds. We shall not linger before this cluster of small stars, which is no doubt nothing but a collection of the dismembered fragments of a planet, which formerly existed in this particular point of space, and was dashed to pieces by some formidable accident in the universe. These little stars, like the important planets, have each their names, such as Vesta, Pallas, Circe, &c., &c. Maximiliana, and Feronia are placed at the two extremities, with respect to distance from the Sun. These remains of a broken star continue to circulate around the Sun, like the planet which they formerly composed.

After the Asteroïds comes great Jupiter.

Jupiter is the largest planetary sphere in our solar system, being 1400 times greater than the Earth. Its distance from the Sun is 200,000,000 miles. In consequence of this distance, its year is as long as twelve of our years. Notwithstanding its colossal dimensions, Jupiter turns with such rapidity upon its axis, that it accomplishes an entire revolution in twelve hours, so that its day and night are respectively only ten hours long. The shortness of Jupiter's nights are compensated by the existence of four moons, or satellites, which revolve around this planet, and give it permanent light. This illumination by reflection, added to very long twilights, must make Jupiter's nights nearly equal to the day in brightness.

Though Jupiter suffers under the disadvantage of very short days, it has on the other hand the inappreciable advantage of perfect equality in the length of its days and nights, and of that of the four seasons over all its parallels. The axis of Jupiter is hardly at all oblique, and therefore Jupiter, like the planet Saturn, enjoys a sort of perpetual spring, that is to say, an equable distribution of solar heat and light along the same degrees of latitude. Jupiter, unlike Mars and Venus, has no vicissitudes of seasons, no sudden and painful transitions from cold to heat in the same place. The climates are invariable in each latitude, and the seasons are hardly discernible.

The globe of Saturn is 734 times larger than that of the Earth, and is 364,000,000 leagues from the Sun. It takes thirty years to perform its revolution around the central star, and its year is therefore thirty times as long as ours.

Saturn, like Jupiter, has very short days. It revolves on its axis in ten hours, so that its day and night respectively are but five hours. But it has eight moons, or satellites, which accompany it, and give it light, thus, as in the case of Jupiter, supplementing the shortness of its days. There is hardly any obliquity of the axis of Saturn, so that its days and nights are always equal. There is a perpetual equinox, and the climates are invariable, while variation of seasons hardly exists. In Saturn, as in Jupiter, perpetual spring reigns. Saturn has one peculiarity which does not belong to any other body in our solar system. It is placed in the centre of a ring, of the same nature as its own, and which surrounds it on every side. This ring (see plate 5), is surrounded by a second, and the second by a third, and the whole are called the rings of Saturn. This circular envelope is exceedingly thin—only ten leagues in thickness—but very wide; its width is 12,000 leagues. It is not motionless, but it revolves with the globe which it surrounds.