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.
[Illustration]
FOOTNOTES:
[5] Represented by the French word _hectare_.
[Illustration]
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.
In the sun seasons are unknown as well as days. Time seems to have no
existence for the beings who occupy that radiant dwelling-place. The
changes, and the succession of things for us which constitute time,
are unknown to their sublime essence. Duration has no measure in that
blessed world.
The dweller in the sun must behold the revolution of the planets around
him, performed according to the same laws, but with different rates of
speed. The phases of the planets and their satellites, the phases of
Mars and Venus, or those of the moon, which we perceive from the earth,
are unknown to them; they see only the hemisphere of those globes which
is illumined by their own immense country. They behold, in larger
dimensions, the globes of Mercury and Venus, and in lesser dimensions
the Earth and Mars. The distant planets, Jupiter, Saturn, and Uranus,
must seem very small to them. Neptune they probably cannot see at
all. The comets must be for a long time invisible to the inhabitants
of the sun, who behold their flaming mass rushing towards them in
ever-increasing size. They also see some comets sinking away into
space, and others falling on the surface of the sun himself, to be lost
and absorbed in his substance.
Thus, the spots on the sun have revealed to us an important peculiarity
of his astronomical character, his revolution upon his axis. They have
also given us the only exact ideas which we possess of the physical
constitution of the sun.
The accompanying plate conveys an idea of what the spots on the sun
consist of. Figures 2 and 3 represent the general aspect of these
appearances. In the centre is a black space perfectly marked. To this
succeeds a space in grey tinting, whose outlines melt by degrees into
the rest of the luminous mass. The first region is called the Umbra;
the second, the Penumbra.
These words must be distinctly understood. The part indicated by the
term _Umbra_ is only dark relatively to the illumined portion. This
Umbra is very luminous, its brilliancy is two thousand times that
of the full moon. We are merely dealing with comparisons here. The
solar spots are often of very considerable dimensions. They have been
found 30,000 leagues in breadth, and could swallow up the earth,
which is only one-tenth of that magnitude. They are not permanent,
sometimes they remain for months, or even years, but the greater
number increase and decrease rapidly, and disappear in a few weeks.
They are incessantly changing in form and in extent, and they grow
and diminish. It is evident that they are regulated by a violent
interior movement, and that they are the seat of tumultuous motion.
Something like whirlwinds are seen to sweep across the regions occupied
by the spots, and to carry them away, like the waves of a furious
sea, or the flames of a conflagration. Gigantic bridges of apparently
burning matter have been observed, thrown from one edge to the other
of adjacent spots, uniting them by a shining band, and then this same
band has stretched itself out and caught hold of other spots. Of a
sudden the whole edifice has been seen to be swept away by fresh
whirlwinds. Signs of a prodigious commotion, of gigantic perturbation,
are always evident. These hurricanes, these tempests of flame, are of
a widely different grandeur from the hurricanes and the tempests of
our atmosphere, because the atmosphere of the sun is several thousands
of yards in height, and covers an extent of surface 1,300,000 times
greater than ours.
[Illustration: Fig. 2.--Group of Solar Spots observed in 1864 by
Nasmith.]
[Illustration: Fig. 3.--Another Solar Spot observed by Nasmyth.]
We have just said that the sun has an atmosphere. Such is the
conclusion to which the careful examination of the great star has led.
From the earliest times at which the sun was observed, a theory of its
constitution was formulated, which was perpetuated down to the present
age, without receiving authoritative contradiction. In the eighteenth
century the astronomers Herschel and Wilson developed this theory,
which was popularized in our time by the writings of Humboldt and Arago.
According to this theory, the sun is composed of a dark nucleus, and
a burning atmosphere, which is the only source of the light proper to
this star. Arago and Humboldt called the incandescent atmosphere of the
sun, the _photosphere_. Heat and light would not, therefore, come to us
from the nucleus, but only from the photosphere.
The spots are explained, according to this theory, by admitting that
they are openings accidentally formed in the sun's atmosphere by
gases discharged from volcanic craters, or in some other way. Through
these openings the dark nucleus of the sun is seen. The _penumbra_ of
the spots are formed by the lower parts of the atmosphere of the sun,
which is either hot or luminous. This lower portion of the atmosphere,
reflecting the light emitted by the upper portion or photosphere, is
slightly warm, and only partially illumined.