Young Folks' Library, Volume XI (of 20) by Various

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In Pholas the light is still more persistent, and it is found that
when the dead body of this mollusk is placed in honey, it will retain
for more than a year the power of emitting light when plunged in warm
water.

The investigations of recent years have rendered it more and more
probable that the light exhibited by phosphorescent organisms is due
to a chemical process somewhat analogous to that which goes on in the
burning of a candle. This latter process is one of rapid oxidation.
The particles of carbon supplied by the oily matter that feeds the
candle become so rapidly combined with oxygen derived from the air
that a considerable amount of light, along with heat, is produced
thereby. Now, the phenomenon of phosphorescence in organic forms,
whether living or dead, appears also to be due to a process of
oxidation, but one that goes on much more slowly than in the case of a
lighted candle. It is thus more closely analogous to what is observed
in the element phosphorus itself, which owes its name (meaning
"light-bearer") to the fact that when exposed to the air at ordinary
temperatures it glows in the dark, in consequence of its becoming
slowly combined with oxygen.

At one time it was believed that the presence of oxygen was not
necessary to the exhibition of phosphorescence in organic forms, but
it has now been placed beyond doubt that this is a mistake. Oxygen has
been proved to be indispensable, and hence we see a reason for the
luminous organs in the glow-worm being so intimately connected, as
above mentioned, with the air-tubes that ramify through the insect.

This fact of itself might be taken as a strong indication of the
chemical nature of the process to which phosphorescence is due. But
the problem has been made the subject of further investigations which
have thrown more light upon it. It was long known that there were
various inorganic bodies besides phosphorus which emitted a
phosphorescent light in the dark, at least after being exposed to the
rays of the sun; but it was not till quite recently that any organic
compound was known to phosphoresce at ordinary temperatures.

This discovery was made by a Polish chemist, named Bronislaus
Radziszewski, who followed it up with a long series of experiments on
the phosphorescence of organic compounds, by which he was able to
determine the conditions under which that phenomenon was exhibited. In
all the substances investigated by him in which phosphorescence was
introduced he found that three conditions were essential to its
production: (1) that oxygen should be present; (2) that there should
be an alkaline reaction in the phosphorescing mixture--that is, a
reaction such as is produced on acids and vegetable coloring matters
by potash, soda, and the other alkalies; and (3) that some kind of
chemical action should take place.

He found, moreover, that among the organic compounds that could be
made to phosphoresce under these conditions were nearly all the fixed
and ethereal oils. With reference to the phosphorescence of animals,
this observation is important, for it has been shown in a great many
cases that a fatty substance forms the main constituent in their
luminous organs. This has long been known to be the case in the
luminous insects belonging to the Lampyridae and Elateridae, as well as
in the luminous centipedes; and the researches of Panceri, already
referred to, on the luminous organs of many marine forms have shown
that it holds good with regard to these also.

We may, therefore, conclude that substances fitted to phosphoresce
under the conditions determined by the experiments of Radziszewski are
generally, and probably universally, present in the luminous organs of
phosphorescent animals. Now, what is to be said as to the occurrence
of these conditions? The access of oxygen is in all cases easy to
account for, but it must also be shown how the alkaline reaction is to
be produced. We need not expect to find in animal organisms potash,
soda, ammonia, and the other common alkalies; but it was established
by experiment that the alkaline organic compounds cholin and neurin,
which are present in animal tissues, would also serve to bring about
the phenomenon of phosphorescence in the substances on which the
experiments were made.

Accordingly, it seems fair to conclude that when all these conditions
for the production of phosphorescence in a chemical laboratory are
present in animal organisms, the phenomenon, when observed in these,
is exactly of the same nature as that which is produced artificially.
By that it is meant that animal phosphorescence is attended, like the
artificial phenomenon, by a slow chemical action, or in other words,
that the phosphorescent light is due to a gradual process of
oxidation.

One curious circumstance has been discovered which lends still further
probability to this explanation. It was mentioned above that among
phosphorescent plants there are several species of Agaricus. Now,
from one species of this genus, though not indeed one of the
phosphorescent species (from _A. muscarius_) there has been extracted
a principle called _amanitia_, which is found to be identical with
cholin. In the light of the results derived from the investigations
just referred to it is reasonable to draw the conclusion that, if
sought for, this principle would likewise be found in the
phosphorescent species in which the other conditions of
phosphorescence are also present.

On this theory of the production of the phenomenon now under
consideration, the effect of shaking or of vital action in giving rise
to or intensifying the exhibition of the light is accounted for by the
fact that by these means fresh supplies of oxygen are brought into
contact with the phosphorescent substance. The effect of ammonia on
the light emitted by the sea-slug _Phyllirhoe bucephala_, is also
fully explained, ammonia being one of those alkaline substances which
are so directly favorable to the exhibition of the phenomenon.

Nor is it difficult to account for the control which in some cases
insects appear to have over the luminosity of the phosphorescent
organs, exhibiting and withdrawing the light at will. It is not
necessary to suppose that this is an immediate effect, a conversion of
nerve force into light, and a withdrawal of that force. The action of
the creature's will may be merely in maintaining or destroying the
conditions under which the light is manifested. It may, for example,
have the power of withdrawing the supply of oxygen, and this
supposition receives some countenance from the observation cited from
Kirby and Spence on the two captured glow-worms, one of which
withdrew its light, while the other kept it shining, but while doing
so had the posterior extremity of the abdomen in constant motion. But
the animal may also have the power in another way of affecting the
chemical conditions of the phenomenon. It may, for example, have the
power of increasing or diminishing by some nervous influence the
supply of the necessary alkaline ingredient.

But if animal phosphorescence is really due to a process of slow
oxidation, there is one singular circumstance to be noted in
connection with it. Oxidation is a process that is normally
accompanied by the development of heat. Even where no light is
produced an increase of temperature regularly takes place when
substances are oxidized. We ought, then, to expect such a rise of
temperature when light is emitted by the phosphorescent organs of
animals. But the most careful observations have shown that nothing of
the kind can be detected. It was with a view to test this that Panceri
dissected out the luminous organs of so many specimens of Pholas. He
selected this mollusk because it was so abundant in the neighborhood
of Naples, where, his experiments were made; and in making his
experiments he made use of a thermopile, an apparatus by which, with
the aid of electricity, much smaller quantities of heat can be
indicated than by means of the most delicate thermometer. The organs
remained luminous long after they were extracted, but no rise in
temperature whatever could be found to accompany the luminosity. Many
experiments upon different animals were made with similar negative
results by means of the thermometer.

The only explanation of this that can be given is probably to be found
in the fact that the chemical process ascertained to go on in the
phosphorescence of organic compounds on which experiments were made in
the laboratory is an extremely slow one.

The so-called phosphorescence of most inorganic bodies is one of a
totally different nature from that exhibited in organic forms. The
diamond shines for a time in the dark after it has been exposed to the
sun; so do pieces of quartz when rubbed together, and powdered
fluor-spar when heated shines with considerable brilliancy. Various
artificial compounds, such as sulphide of calcium (Canton's
phosphorus, as it is called from the discoverer), sulphate of barium
(Bologna stone, or Bologna phosphorus), sulphide of strontium, etc.,
after being illuminated by the rays of the sun, give out in the dark a
beautiful phosphorescence, green, blue, violet, orange, red, according
to circumstances. The luminous paint which has recently attracted so
much attention is of the same nature. In these cases what we have is
either a conversion of heat rays into light rays (as in the powdered
fluor-spar), or the absorption and giving out again of sun-rays. In
the latter case the phenomenon is essentially the same as
fluorescence, in which the dark rays of the solar spectrum beyond the
violet are made visible.

But we must now return to the other questions that have been started
in relation to phosphorescence in animals. There has been much
speculation as to the object of this light, and to the purposes it
serves in Nature. Probably no general answer can be given to this
question. It is no doubt impossible to show why so many animals have
been endowed with this remarkable property; but we may consider some
of the effects which the possession of it has in different cases.

In the first place, it will undoubtedly serve in many cases to afford
light to enable the animal to see by, and in the Lampyridae it would
seem that the degree of luminosity is related to the development of
the vision. In that family, according to the Rev. H.S. Gorham, the
eyes are developed, as a rule, in inverse proportion to the
luminosity. Where there is an ample supply of this kind of light the
eyes are small, but where the light is insignificant the eyes are
large by way of compensation. And moreover, where both eyes and light
are small, then the antennae are large and feathery, so that the
deficiency in the sense of sight is made up for by an unusual
development in the organs of touch.

But it is none the less certain that the presence of this light cannot
always be designed to serve this purpose, for many of the animals so
endowed are blind. The phosphorescent centipedes are without eyes,
like all the other members of the genus (_Geophilus_) to which they
belong, and probably the majority of phosphorescent marine forms are
likewise destitute of organs of sight.

Another suggestion is that the light derived from these marine forms,
and especially from deep-sea Alcyonarians, is what enables the members
of the deep-sea fauna that are possessed of eyes (which are always
enormously enlarged) to see. Such is the suggestion of Dr. Carpenter,
Sir Wyville Thomson, and Mr. Gwyn Jeffries; and it is possible that
this actually is one of the effects of the phosphorescent property.
But if so, it remains to inquire how the forms endowed with it came
to be possessed of a power useful in that way to other forms, but not
to themselves. According to the Darwinian doctrine of development, the
powers that are developed in different organisms by the process of
natural selection are such as are useful to themselves and not to
others, unless incidentally.

This consideration has led to another suggestion, namely, that the
property of phosphorescence serves as a protection to the forms
possessing it, driving away enemies in one way or another: it may be
by warning them of the fact that they are unpalatable food, as is
believed to be the case with the colors of certain brilliantly-colored
caterpillars; it may be in other ways. In Kirby and Spence one case is
recorded in which the phosphorescence of the common phosphorescent
centipede (_Geophilus electricus_) was actually seen apparently to
serve as a means of defence against an enemy. "Mr. Shepherd," says
that authority, "once noticed a scarabeus running round the
last-mentioned insect when shining, as if wishing, but afraid to
attack it." In the case of the jelly-fishes, it has been pointed out
that their well-known urticating or stinging powers would make them at
least unpleasant, if not dangerous, food for fishes; and that
consequently the luminosity by which so many of them are characterized
at night may serve at once as a warning to predatory fishes and as a
protection to themselves. The experience of the unpleasant properties
of many phosphorescent animals may likewise have taught fishes to
avoid all forms possessing this attribute, even though many of them
might be quite harmless.

Lastly, it has been suggested that the phosphorescence in the female
glow-worm may be designed to attract the male; and that it will
actually have this effect may readily be taken for granted.
Observation shows that the male glow-worm is very apt to be attracted
by a light. Gilbert White of Selborne mentions that they, attracted by
the light of the candles, came into his parlor. Another observer
states that by the same light he captured as many as forty male
glow-worms in one night.

[Illustration]

COMETS

(FROM MARVELS OF THE HEAVENS.)

BY CAMILLE FLAMMARION.

"Je viens vous annoncer une grande nouvelle:
Nous l'avons, en dormant, madame, echappe belle.
Un monde pres de nous a passe tout du long,
Est chu tout au travers de notre tourbillon;
Et s'il eut en chemin rencontre notre terre,
Elle eut ete brisee en morceaux comme verre."
MOLIERE.

[Illustration]

This announcement of Trissontin's to Philaminte, who begins the parody
on the fears caused by the appearance of comets, would not have been a
parody four or five centuries ago. These tailed bodies, which suddenly
come to light up the heavens, were for long regarded with terror, like
so many warning signs of divine wrath. Men have always thought
themselves much more important than they really are in the universal
order; they have had the vanity to pretend that the whole creation was
made for them, whilst in reality the whole creation does not suspect
their existence. The Earth we inhabit is only one of the smallest
worlds; and therefore it can scarcely be for it alone that all the
wonders of the heavens, of which the immense majority remains hidden
from it, were created. In this disposition of man to see in himself
the centre and the end of everything, it was easy indeed to consider
the steps of nature as unfolded in his favor; and if some unusual
phenomenon presented itself, it was considered to be without doubt a
warning from Heaven. If these illusions had had no other result than
the amelioration of the more timorous of the community one would
regret these ages of ignorance; but not only were these fancied
warnings of no use, seeing that once the danger passed, man returned
to his former state; but they also kept up among people imaginary
terrors, and revived the fatal resolutions caused by the fear of the
end of the world.

When one fancies the world is about to end,--and this has been
believed for more than a thousand years,--no solicitude is felt in the
work of improving this world; and, by the indifference or disdain into
which one falls, periods of famine and general misery are induced
which at certain times have overtaken our community. Why use the
wealth of a world which is going to perish? Why work, be instructed,
or rise in the progress of the sciences or arts? Much better to forget
the world, and absorb one's self in the barren contemplation of an
unknown life. It is thus that ages of ignorance weigh on man, and
thrust him further and further into darkness, while Science makes
known by its influence on the whole community, its great value, and
the magnitude of its aim.

The history of a comet would be an instructive episode of the great
history of the heavens. In it could be brought together the
description of the progressive movement of human thought, as well as
the astronomical theory of these extraordinary bodies. Let us take,
for example, one of the most memorable and best-known comets, and give
an outline of its successive passages near the Earth. Like the
planetary worlds, Comets belong to the solar system, and are subject
to the rule of the Star King. It is the universal law of gravitation
which guides their path; solar attraction governs them, as it governs
the movement of the planets and the small satellites. The chief point
of difference between them and the planets is, that their orbits are
very elongated; and, instead of being nearly circular, they take the
elliptical form. In consequence of the nature of these orbits, the
same comet may approach very near the Sun, and afterwards travel from
it to immense distances. Thus, the period of the Comet of 1680 has
been estimated at three thousand years. It approaches the Sun, so as
to be nearer to it than our Moon is to us, whilst it recedes to a
distance 853 times greater than the distance of the Earth from the
Sun. On the 17th of December, 1680, it was at its perihelion--that is,
at its greatest proximity to the Sun; it is now continuing its path
beyond the Neptunian orbit. Its velocity varies according to its
distance from the solar body. At its perihelion it travels thousands
of leagues per minute; at its aphelion it does not pass over more than
a few yards. Its proximity to the Sun in its passage near that body
caused Newton to think that it received a heat twenty-eight thousand
times greater than that we experience at the summer solstice; and
that this heat being two thousand times greater than that of red-hot
iron, an iron globe of the same dimensions would be fifty thousand
years entirely losing its heat. Newton added that in the end comets
will approach so near the Sun that they will not be able to escape the
preponderance of its attraction, and that they will fall one after the
other into this brilliant body, thus keeping up the heat which it
perpetually pours out into space. Such is the deplorable end assigned
to comets by the author of the "Principia," an end which makes De la
Bretonne say to Retif: "An immense comet, already larger than Jupiter,
was again increased in its path by being blended with six other dying
comets. Thus displaced from its ordinary route by these slight shocks,
it did not pursue its true elliptical orbit; so that the unfortunate
thing was precipitated into the devouring centre of the Sun." "It is
said," added he, "that the poor comet, thus burned alive, sent forth
dreadful cries!"

[Illustration: A COMET]

It will be interesting, then, in a double point of view, to follow a
comet in its different passages in sight of the Earth. Let us take the
most important in astronomical history--the one whose orbit has been
calculated by Edmund Halley, and which was named after him. It was in
1682 that this comet appeared in its greatest brilliancy, accompanied
with a tail which did not measure less than thirty-two millions of
miles. By the observation of the path which it described in the
heavens, and the time it occupied in describing it, this astronomer
calculated its orbit, and recognized that the comet was the same as
that which was admired in 1531 and 1607, and which ought to have
reappeared in 1759. Never did scientific prediction excite a more
lively interest. The comet returned at the appointed time; and on the
12th of March, 1759, reached its perihelion. Since the year 12 before
the Christian era, it had presented itself twenty-four times to the
Earth. It was principally from the astronomical annals of China that
it was possible to follow it up to this period.

Its first memorable appearance in the history of France is that of
837, in the reign of Louis le Debonnaire. An anonymous writer of
chronicles of that time, named "The Astronomer," gave the following
details of this appearance, relative to the influence of the comet on
the imperial imagination:

"During the holy days of the solemnization of Easter, a phenomenon
ever fatal, and of gloomy foreboding, appeared in the heavens. As soon
as the Emperor, who paid attention to these phenomena, received the
first announcement of it, he gave himself no rest until he had called
a certain learned man and myself before him. As soon as I arrived, he
anxiously asked me what I thought of such a sign; I asked time of him,
in order to consider the aspects of the stars, and to discover the
truth by their means, promising to acquaint him on the morrow; but the
Emperor, persuaded that I wished to gain time, which was true, in
order not to be obliged to announce anything fatal to him, said to me:
'Go on the terrace of the palace and return at once to tell me what
you have seen, for I did not see this star last evening, and you did
not point it out to me; but I know that it is a comet; tell me what
you think it announces to me.' Then scarcely allowing me time to say
a word, he added: 'There is still another thing you keep back; it is
that a change of reign and the death of a prince are announced by this
sign.' And as I advanced the testimony of the prophet, who said: 'Fear
not the signs of the heavens as the nations fear them,' the prince
with his grand nature, and the wisdom which never forsook him, said,
'We must not only fear Him who has created both us and this star. But
as this phenomenon may refer to us, let us acknowledge it as a warning
from Heaven."

Louis le Debonnaire gave himself and his court to fasting and prayer,
and built churches and monasteries. He died three years later, in 840,
and historians have profited by this slight coincidence to prove that
the appearance of the comet was a harbinger of death. The historian,
Raoul Glader, added later: "These phenomena of the universe are never
presented to man without surely announcing some wonderful and terrible
event."

Halley's comet again appeared in April, 1066, at the moment when
William the Conqueror invaded England. It was pretended that it had
the greatest influence on the fate of the battle of Hastings, which
delivered over the country to the Normans.

A contemporary poet, alluding probably to the English diadem with
which William was crowned, had proclaimed in one place, "that the
comet had been more favorable to William than nature had been to
Caesar; the latter had no hair, but William had received some from the
comet." A monk of Malmesbury apostrophized the comet in these terms:
"Here thou art again, thou cause of the tears of many mothers! It is
long since I have seen thee, but I see thee now, more terrible than
ever; thou threatenest my country with complete ruin!"

In 1455, the same comet made a more memorable appearance still. The
Turks and Christians were at war, the West and the East seemed armed
from head to foot--on the point of annihilating each other. The
crusade undertaken by Pope Calixtus III. against the invading
Saracens, was waged with redoubled ardor on the sudden appearance of
the star with the flaming tail. Mahomet II. took Constantinople by
storm, and raised the siege of Belgrade. But the Pope having put aside
both the curse of the comet, and the abominable designs of the
Mussulmans, the Christians gained the battle, and vanquished their
enemies in a bloody fight. The _Angelus_ to the sound of bells dates
from these ordinances of Calixtus III. referring to the comet.

In his poem on astronomy, Daru, of the French Academy, describes this
episode in eloquent terms:

"Un autre Mahomet a-t-il d'un bras puissant
Aux murs de Constantine arbore le croissant:
Le Danube etonne se trouble au bruit des armes,
La Grece est dans les fers, l'Europe est en alarmes;
Et pour comble d'horreur, l'astre au visage ardent
De ses ailes de feu va couvrir l'Occident.
Au pied de ses autels, qu'il ne saurait defendre,
Calixte, l'oeil en pleurs, le front convert de cendre,
Conjure la comete, objet de tant d'effroi:
Regarde vers les cieux, pontife, et leve-toi!
L'astre poursuit sa course, et le fer d'Huniade
Arrete le vainqueur, qui tombe sous Belgrade.
Dans les cieux cependant le globe suspendu,
Par la loi generale a jamais retenu,
Ignore les terreurs, l'existence de Rome,
Et la Terre peut-etre, et jusqu'au nom de l'homme,
De l'homme, etre credule, atome ambitieux,
Qui tremble sous un pretre et qui lit dans les cieux."

This ancient comet witnessed many revolutions in human history, at
each of its appearances, even in its later ones, in 1682, 1759, 1835;
it was also presented to the Earth under the most diverse aspects,
passing through a great variety of forms, from the appearance of a
curved sabre, as in 1456, to that of a misty head, as in its last
visit. Moreover, this is not an exception to the general rule, for
these mysterious stars have had the gift of exercising a power on the
imagination which plunged it in ecstasy or trouble. Swords of fire,
bloody crosses, flaming daggers, spears, dragons, fish, and other
appearances of the same kind, were given to them in the middle ages
and the Renaissance.

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