In 1843 a comet appeared which was so brilliant that it could be seen

in broad day close beside the sun! This was the first authenticated

instance of that kind, but the occurrence was to be repeated, as we

shall see in a moment, less than forty years later.

The splendid comet of 1858, usually called Donati’s, is remembered by

many persons yet living. It was, perhaps, both as seen by the naked eye

and with the telescope, the most beautiful comet of which we have any

record. It too marked a rich vintage year, still remembered in the

vineyards of France, where there is a popular belief that a great comet

ripens the grape and imparts to the wine a flavor not attainable by the

mere skill of the cultivator. There are “comet wines,” carefully

treasured in certain cellars, and brought forth only when their owner

wishes to treat his guests to a sip from paradise.

The year 1861 saw another very remarkable comet, of an aspect strangely

vast and diffuse, which is believed to have swept the earth with its

immense tail when it passed between us and the sun on the night of June

30th, an event which produced no other known effect than the appearance

of an unwonted amount of scattered light in the sky.

The next very notable comet was the “Great Southern Comet” of 1880,

which was not seen from the northern hemisphere. It mimicked the aspect

of the famous comet of 1843, and to the great surprise of astronomers

appeared to be traveling in the same path. This proved to be the rising

of the curtain for an astronomical sensation unparalleled in its kind;

for two years later another brilliant comet appeared, first in the

southern hemisphere, _and it too followed the same track._ The

startling suggestion was now made that this comet was identical with

those of 1843 and 1880, its return having been hastened by the

resistance experienced in passing twice through the coronal envelope,

and there were some who thought that it would now swing swiftly round

and then plunge straight into the sun, with consequences that might be

disastrous to us on account of the “flash of heat” that would be

produced by the impact. Nervous people were frightened, but observation

soon proved that the danger was imaginary, for although the comet

almost grazed the sun, and must have rushed through two or three

million miles of the coronal region, no retardation of its immense

velocity was perceptible, and it finally passed away in a damaged

condition, as before remarked, and has never since appeared.

Then the probable truth was perceived—_viz.,_ that the three comets

(1843, 1880, and 1882) were not one identical body, but three separate

ones all traveling in the same orbit. It was found, too, that a comet

seen in 1668 bore similar insignia of relationship. The natural

inference was that these four bodies had once formed a single mass

which had been split apart by the disruptive action of the sun.

Strength was lent to this hypothesis by the fact that the comet of 1882

was apparently torn asunder during its perihelion passage, retreating

into space in a dissevered state. But Prof. George Forbes has a theory

that the splitting of the original cometary mass was effected by an

unknown planet, probably greater than Jupiter, situated at a hundred

times the earth’s distance from the sun, and revolving in a period of a

thousand years. He supposes that the original comet was not that of

1668, but one seen in 1556, which has since been “missing,” and that

its disruption occurred from an encounter with the supposititious

planet about the year 1700. Truly from every point of view comets are

the most extraordinary of adventurers!

The comet of 1882 was likewise remarkable for being visible, like its

predecessor of 1843, in full daylight in close proximity to the sun.

The story of its detection when almost in contact with the solar disk

is dramatic. It had been discovered in the southern hemisphere only a

couple of weeks before its perihelion, which occurred on September

17th, and on the forenoon of that day it was seen by Doctor Common in

England, and by Doctor Elkin and Mr Finlay at the Cape of Good Hope,

almost touching the sun. It looked like a dazzling white bird with

outspread wings. The southern observers watched it go _right into the

sun,_ when it instantly disappeared. What had happened was that the

comet in passing its perihelion point had swung exactly between the

earth and the sun. On the following morning it was seen from all parts

of the world close by the sun on the opposite side, and it remained

thus visible for three days, gradually receding from the solar disk. It

then became visible for northern observers in the morning sky before

sunrise, brandishing a portentous sword-shaped tail which, if it had

been in the evening sky, would have excited the wonder of hundreds of

millions, but situated where it was, comparatively few ever saw it.

[Illustration: Daniels’ comet. August 11, 1907]

The application of photography to the study of comets has revealed many

curious details which might otherwise have escaped detection, or at

best have remained subject to doubt. It has in particular shown not

only the precise form of the tails, but the remarkable vicissitudes

that they undergo. Professor Barnard’s photographs of Brooks’ comet in

1893 suggested, by the extraordinary changes in the form of the tail

which they revealed, that the comet was encountering a series of

obstructions in space which bent and twisted its tail into fantastic

shapes. The reader will observe the strange form into which the tail

was thrown on the night of October 21st. A cloud of meteors through

which the comet was passing might have produced such deformations of

its tail. In the photograph of Daniels’ comet of 1907, a curious

striping of the tail will be noticed. The short bright streaks seen in

the photograph, it may be explained, are the images of stars which are

drawn out into lines in consequence of the fact that the photographic

telescope was adjusted to follow the motion of the comet while the

stars remained at rest.

But the adventures of comets are not confined to possible encounters

with unknown obstacles. We have referred to the fact that the great

planets, and especially Jupiter, frequently interfere with the motions

of comets. This interference is not limited to the original alteration

of their orbits from possible parabolas to ellipses, but is sometimes

exercised again and again, turning the bewildered comets into

elliptical paths of all degrees of eccentricity. A famous example of

this kind of planetary horse-play is furnished by the story of Lexell’s

missing comet. This comet was first seen in 1770. Investigation showed

that it was moving in an orbit which should bring it back to perihelion

every five and a half years; yet it had never been seen before and,

although often searched for, has never been seen since. Laplace and

Leverrier proved mathematically that in 1767 it had approached so close

to Jupiter as to be involved among the orbits of his satellites. What

its track had been before is not known, but on that occasion the giant

planet seized the interloper, threw it into a short elliptic orbit and

sent it, like an arrested vagrant, to receive sentence at the bar of

the sun. On this journey it passed within less than 1,500,000 miles of

the earth. The form of orbit which Jupiter had impressed required, as

we have said, its return in about five and a half years; but soon after

1770 it had the misfortune a second time to encounter Jupiter at close

range, and he, as if dissatisfied with the leniency of the sun, or

indignant at the stranger’s familiarity, seized the comet and hurled it

out of the system, or at any rate so far away that it has never since

been able to rejoin the family circle that basks in the immediate rays

of the solar hearth. Nor is this the only instance in which Jupiter has

dealt summarily with small comets that have approached him with too

little deference.

[Illustration: Brooks’ comet. Photographed by Barnard, October 21,

1893]

The function which Jupiter so conspicuously fulfills as master of the

hounds to the sun is worth considering a little more in detail. To

change the figure, imagine the sun in its voyage through space to be

like a majestic battleship surrounded by its scouts. Small vessels (the

comets, as they are overhauled by the squadron, are taken in charge by

the scouts, with Jupiter for their chief, and are forced to accompany

the fleet, but not all are impressed. If a strange comet undertakes to

run across Jupiter’s bows the latter brings it to, and makes prize of

it by throwing it into a relatively small ellipse with the sun for its

focus. Thenceforth, unless, as happened to the unhappy comet of Lexell,

it encounters Jupiter again in such a way as to be diverted by him into

a more distant orbit, it can never get away. About thirty comets are

now known to have thus been captured by the great planet, and they are

called “Jupiter’s Comet Family.” But, on the other hand, if a wandering

comet crosses the wake of the chief planetary scout the latter simply

drives it away by accelerating its motion and compels it to steer off

into open space. The transformation of comets into meteors will be

considered in the next chapter, but here, in passing, mention may be

made of the strange fate of one member of Jupiter’s family, Biela’s

comet, which, having become over bold in its advances to its captor,

was, after a few revolutions in is impressed orbit, torn to pieces and

turned into a flock of meteors.

And now let us return to the mystery of comets’ tails. That we are

fully justified in speaking of the tails of comets as mysterious is

proved by the declaration of Sir John Herschel, who averred, in so many

words, that “there is some profound secret and mystery of nature

concerned in this phenomenon,” and this profound secret and mystery has

not yet been altogether cleared up. Nevertheless, the all-explaining

hypothesis of Arrhenius offers us once more a certain amount of aid.

Comets’ tails, Arrhenius assures us, are but another result of the

pressure of light. The reader will recall the applications of this

theory to the Zodiacal Light and the Aurora. In the form in which we

now have to deal with it, the supposition is made that as a comet

approaches the sun eruptions of vapor, due to the solar heat, occur in

its nucleus. These are naturally most active on the side which is

directly exposed to the sun, whence the appearance of the immense

glowing envelopes that surround the nucleus on the sunward side. Among

the particles of hydro-carbon, and perhaps solid carbon in the state of

fine dust, which are thus set free there will be many whose size is

within the critical limit which enables the light-waves from the sun to

drive them away. Clouds of such particles, then, will stream off behind

the advancing comet, producing the appearance of a tail. This accounts

for the fact that the tails of comets are always directed away from the

sun, and it also explains the varying forms of the tails and the

extraordinary changes that they undergo. The speed of the particles

driven before the light-waves must depend upon their size and weight,

the lightest of a given size traveling the most swiftly. By accretion

certain particles might grow, thus losing velocity and producing the

appearance of bunches in the tail, such as have been observed. The

hypothesis also falls in with the researches of Bredichin, who has

divided the tails of comets into three principal classes—_viz.:_ (1)

Those which appear as long, straight rays; (2) Those which have the

form of curved plumes or scimitars; (3) Those which are short, brushy,

and curved sharply backward along the comet’s path. In the first type

he calculates the repulsive force at from twelve to fifteen times the

force of gravity; in the second at from two to four times; and in the

third at about one and a half times. The straight tails he ascribes to

hydrogen because the hydrogen atom is the lightest known; the

sword-shaped tails to hydro-carbons; and the stumpy tails to vaporized

iron. It will be seen that, if the force driving off the tails is that

which Arrhenius assumes it to be, the forms of those appendages would

accord with those that Bredichin’s theory calls for. At the same time

we have an explanation of the multiple tails with which some comets

have adorned themselves. The comet of 1744, for instance, had at one

time no less than seven tails spread in a wide curved brush behind it.

Donati’s comet of 1858 also had at least two tails, the principal one

sword-shaped and the other long, narrow, and as straight as a rule.

According to Bredichin, the straight tail must have been composed of

hydrogen, and the other of some form of hydro-carbon whose atoms are

heavier than those of hydrogen, and, consequently, when swept away by

the storm of light-waves, followed a curvature depending upon the

resultant of the forces operating upon them. The seven tails of the

comet of 1744 presented a kind of diagram graphically exhibiting its

complex composition, and, if we knew a little more about the

constituents of a comet, we might be able to say from the amount of

curvature of the different tails just what were the seven substances of

which that comet consisted.

If these theories seem to the reader fantastic, at any rate they are no

more fantastic than the phenomena that they seek to explain.

XI

Meteors, Fire-Balls, and Meteorites

One of the most terrorizing spectacles with which the heavens have ever

caused the hearts of men to quake occurred on the night of November 13,

1833. On that night North America, which faced the storm, was under a

continual rain of fire from about ten o’clock in the evening until

daybreak.

_The fragments of a comet had struck the earth._

But the meaning of what had happened was not discovered until long

afterward. To the astronomers who, with astonishment not less than that

of other people, watched the wonderful scene, it was an unparalleled

“shower of meteors.” They did not then suspect that those meteors had

once formed the head of a comet. Light dawned when, a year later, Prof.

Denison Olmsted, of Yale College, demonstrated that the meteors had all

moved in parallel orbits around the sun, and that these orbits

intersected that of the earth at the point where our planet happened to

be on the memorable night of November 13th. Professor Olmsted even went

so far as to suggest that the cloud of meteors that had encountered the

earth might form a diffuse comet; but full recognition of the fact that

they were cometary débris came later, as the result of further

investigation. The key to the secret was plainly displayed in the

spectacle itself, and was noticed without being understood by thousands

of the terror-stricken beholders. It was _an umbrella of fire_ that had

opened overhead and covered the heavens; in other words, the meteors

all radiated from a particular point in the constellation Leo, and,

being countless as the snowflakes in a winter tempest, they ribbed the

sky with fiery streaks. Professor Olmsted showed that the radiation of

the meteors from a fixed point was an effect of perspective, and in

itself a proof that they were moving in parallel paths when they

encountered the earth. The fact was noted that there had been a

similar, but incomparably less brilliant, display of meteors on the

same day of November, 1832, and it was rightly concluded that these had

belonged to the same stream, although the true relationship of the

phenomena was not immediately apprehended. Olmsted ascribed to the

meteors a revolution about the sun once in every six months, bringing

them to the intersection of their orbit with that of the earth every

November 13th; but later investigators found that the real period was

about thirty-three and one-quarter years, so that the great displays

were due three times in a century, and their return was confidently

predicted for the year 1866. The appearance of the meteors in 1832, a

year before the great display, was ascribed to the great length of the

stream which they formed in space—so great that they required more than

two years to cross the earth’s orbit. In 1832 the earth had encountered

a relatively rare part of the stream, but in 1833, on returning to the

crossing-place, it found there the richest part of the stream pouring

across its orbit. This explanation also proved to be correct, and the

predicted return in 1866 was duly witnessed, although the display was

much less brilliant than in 1833. It was followed by another in 1867.

[Illustration: Curious forms of meteorite trains

Nos. 1 to 6 show the changes undergone by a train left by a meteorite

which passed near the “Great Dipper”; 7 shows the changes and drift of

a train seen in the constellation Virgo; 8 is the singular train of the

meteorite of February 22, 1909, near the Pole Star. (From _La

Nature_.)]

In the mean time Olmsted’s idea of a cometary relationship of the

meteors was demonstrated to be correct by the researches of

Schiaparelli and others, who showed that not only the November meteors,

but those of August, which are seen more or less abundantly every year,

traveled in the tracks of well-known comets, and had undoubtedly an

identical origin with those comets. In other words the comets and the

meteor-swarms were both remnants of original masses which had probably

been split up by the action of the sun, or of some planet to which they

had made close approaches. The annual periodicity of the August meteors

was ascribed to the fact that the separation had taken place so long

ago that the meteors had become distributed all around the orbit, in

consequence of which the earth encountered some of them every year when

it arrived at the crossing-point. Then Leverrier showed that the

original comet associated with the November meteors was probably

brought into the system by the influence of the planet Uranus in the

year 126 of the Christian era. Afterward Alexander Herschel identified

the tracks of no less than seventy-six meteor-swarms (most of them

inconspicuous) with those of comets. The still more recent researches

of Mr W. F. Denning make it probable that there are no meteors which do

not belong to a flock or system probably formed by the disintegration

of a cometary mass; even the apparently sporadic ones which shoot

across the sky, “lost souls in the night,” being members of flocks

which have become so widely scattered that the earth sometimes takes

weeks to pass through the region of space where their paths lie.

The November meteors should have exhibited another pair of spectacles

in 1899 and 1900, and their failure to do so caused at first much

disappointment, until it was made plain that a good reason existed for

their absence. It was found that after their last appearance, in 1867,

they had been disturbed in their movements by the planets Jupiter and

Saturn, whose attractions had so shifted the position of their orbit

that it no longer intersected that of the earth, as it did before.

Whether another planetary interference will sometime bring the

principal mass of the November meteors back to the former point of

intersection with the earth’s orbit is a question for the future to

decide. It would seem that there may be several parallel streams of the

November meteors, and that some of them, like those of August, are

distributed entirely around the orbit, so that every mid-November we

see a few of them.

We come now to a very remarkable example of the disintegration of a

comet and the formation of a meteor-stream. In 1826 Biela, of

Josephstadt, Austria, discovered a comet to which his name was given.

Calculation showed that it had an orbital period of about six and a

half years, belonging to Jupiter’s “family.” On one of its returns, in

1846, it astonished its watchers by suddenly splitting in two. The two

comets thus formed out of one separated to a distance of about one

hundred and sixty thousand miles, and then raced side by side,

sometimes with a curious ligature connecting them, like Siamese twins,

until they disappeared together in interplanetary space. In 1852 they

came back, still nearly side by side, but now the distance between them

had increased to a million and a quarter of miles. After that, at every

recurrence of their period, astronomers looked for them in vain, until

1872, when an amazing thing happened. On the night of November 28th,

when the earth was crossing the plane of the orbit of the missing

comet, a brilliant shower of meteors burst from the northern sky,

traveling nearly in the track which the comet should have pursued. The

astronomers were electrified. Klinkerfues, of Göttingen, telegraphed to

Pogson, of Madras: _“Biela touched earth; search near Theta Centauri.”_

Pogson searched in the place indicated and saw a cometary mass

retreating into the southern heavens, where it was soon swallowed from

sight!

[Illustration: Section of the atmosphere up to 100 kilometers.

Showing the mean elevation at which meteorites and meteors make their

appearance. Below are shown the elevation of Mount Everest, the highest

manned balloon ascent by M. Berson; the height of cirrus clouds; the

highest free balloon ascent; and the elevation attained by the clouds

of fire-dust ejected by the Krakatoa eruption in 1883. (From _La

Nature_)]

Since then the Biela meteors have been among the recognized periodic

spectacles of the sky, and few if any doubt that they represent a

portion of the missing comet whose disintegration began with the

separation into two parts in 1846. The comet itself has never since

been seen. The first display of these meteors, sometimes called the

“Andromedes,” because they radiate from the constellation Andromeda,

was remarkable for the great brilliancy of many of the fire-balls that

shot among the shower of smaller sparks, some of which were described

as equaling the full moon in size. None of them is known to have

reached the earth, but during the display of the same meteors in 1885 a

meteoric mass fell at Mazapil in Northern Mexico (it is now in the

Museum at Vienna), which many have thought may actually be a piece of

the original comet of Biela. This brings us to the second branch of our

subject.

More rare than meteors or falling stars, and more startling, except

that they never appear in showers, are the huge balls of fire which

occasionally dart through the sky, lighting up the landscapes beneath

with their glare, leaving trains of sparks behind them, often producing

peals of thunder when they explode, and in many cases falling upon the

earth and burying themselves from a few inches to several feet in the

soil, from which, more than once, they have been picked up while yet

hot and fuming. These balls are sometimes called bolides. They are not

really round in shape, although they often look so while traversing the

sky, but their forms are fragmentary, and occasionally fantastic. It

has been supposed that their origin is different from that of the true

meteors; it has even been conjectured that they may have originated

from the giant volcanoes of the moon or have been shot out from the sun

during some of the tremendous explosions that accompany the formation

of eruptive prominences. By the same reasoning some of them might be

supposed to have come from some distant star. Others have conjectured

that they are wanderers in space, of unknown origin, which the earth

encounters as it journeys on, and Lord Kelvin made a suggestion which

has become classic because of its imaginative reach—_viz.,_ that the

first germs of life may have been brought to the earth by one of these

bodies, “a fragment of an exploded world.”

It is a singular fact that astronomers and scientific men in general

were among the last to admit the possibility of solid masses falling

from the sky. The people had believed in the reality of such phenomena

from the earliest times, but the savants shook their heads and talked

of superstition. This was the less surprising because no scientifically

authenticated instance of such an occurrence was known, and the stones

popularly believed to have fallen from the sky had become the objects

of worship or superstitious reverence, a fact not calculated to

recommend them to scientific credence. The celebrated “black stone”

suspended in the Kaaba at Mecca is one of these reputed gifts from

heaven; the “Palladium” of ancient Troy was another; and a stone which

fell near Ensisheim, in Germany, was placed in a church as an object to

be religiously venerated. Many legends of falling stones existed in

antiquity, some of them curiously transfigured by the imagination, like

the “Lion of the Peloponnesus,” which was said to have sprung down from

the sky upon the Isthmus of Corinth. But near the beginning of the

nineteenth century, in 1803, a veritable shower of falling stones

occurred at L’Aigle, in Northern France, and this time astronomers took

note of the phenomenon and scientifically investigated it. Thousands of

the strange projectiles came from the sky on this occasion, and were

scattered over a wide area of country, and some buildings were hit.

Four years later another shower of stones occurred at Weston, Conn.,

numbering thousands of individuals. The local alarm created in both

cases was great, as well it might be, for what could be more

intimidating than to find the blue vault of heaven suddenly hurling

solid missiles at the homes of men? After these occurrences it was

impossible for the most skeptical to doubt any longer, and the regular

study of “aerolites,” or “meteorites,” began.

One of the first things recognized was the fact that fire-balls are

solid meteorites in flight, and not gaseous exhalations in the air, as

some had assumed. They burn in the air during their flight, and

sometimes, perhaps, are entirely consumed before reaching the ground.

Their velocity before entering the earth’s atmosphere is equal to that

of the planets in their orbits—_viz.,_ from twenty to thirty miles per

second—a fact which proves that the sun is the seat of the central

force governing them. Their burning in the air is not difficult to

explain; it is the heat of friction which so quickly brings them to

incandescence. Calculation shows that a body moving through the air at

a velocity of about a mile per second will be brought, superficially,

to the temperature of “red heat” by friction with the atmosphere. If

its velocity is twenty miles per second the temperature will become

thousands of degrees. This is the state of affairs with a meteorite

rushing into the earth’s atmosphere; its surface is liquefied within a

few seconds after the friction begins to act, and the melted and

vaporized portion of its mass is swept backward, forming the train of

sparks that follows every great fire-ball. However, there is one

phenomenon connected with the trains of meteorites which has never been

satisfactorily explained: they often persist for long periods of time,

drifting and turning with the wind, but not ceasing to glow with a

phosphorescent luminosity. The question is, Whence comes this light? It

must be light without heat, since the fine dust or vapor of which the

train can only consist would not retain sufficient heat to render it

luminous for so long a time. An extremely remarkable incident of this

kind occurred on February 22, 1909, when an immense fire-ball that

passed over southern England left a train that remained visible during

two hours, assuming many curious shapes as it was drifted about by

currents in the air.

[Illustration: A meteor photographed in flight]

But notwithstanding the enormous velocity with which meteorites enter

the air they are soon slowed down to comparatively moderate speed, so

that when they disappear they are usually traveling not faster than a

mile a second. The courses of many have been traced by observers

situated along their track at various points, and thus a knowledge has

been obtained of their height above the ground during their flight and

of the length of their visible courses. They generally appear at an

elevation of eighty or a hundred miles, and are seldom visible after

having descended to within five miles of the ground, unless the

observer happens to be near the striking-point, when he may actually

witness the fall. Frequently they burst while high in the air and their

fragments are scattered like shrapnel over the surface of the ground,

sometimes covering an area of several square miles, but of course not

thickly; different fragments of the same meteorite may reach the ground

at points several miles apart. The observed length of their courses in

the atmosphere varies from fifty to five hundred miles. If they

continued a long time in flight after entering the air, even the

largest of them would probably be consumed to the last scrap, but their

fiery career is so short on account of their great speed that the heat

does not have time to penetrate very deeply, and some that have been

picked up immediately after their fall have been found cold as ice

within. Their size after reaching the ground is variable within wide

limits; some are known which weigh several tons, but the great majority

weigh only a few pounds and many only a few ounces.

Meteorites are of two kinds: _stony_ meteorites and _iron_ meteorites.

The former outnumber the latter twenty to one; but many stone

meteorites contain grains of iron. Nickel is commonly found in iron

meteorites, so that it might be said that that redoubtable alloy

nickel-steel is of cosmical invention. Some twenty-five chemical

elements have been found in meteorites, including carbon and the

“sun-metal,” helium. The presence of the latter is certainly highly

suggestive in connection with the question of the origin of meteorites.

The iron meteorites, besides metallic iron and nickel, of which they

are almost entirely composed, contain hydrogen, helium, and carbonic

oxide, and about the only imaginable way in which these gases could

have become absorbed in the iron would be through the immersion of the

latter while in a molten or vaporized state in a hot and dense

atmosphere composed of them, a condition which we know to exist only in

the envelopes of the sun and the stars.

The existence of carbon in the Canyon Diablo iron meteorites is

attended by a circumstance of the most singular character—a very “fairy

tale of science.” In some cases _the carbon has become diamond!_ These

meteoric diamonds are very small; nevertheless, they are true diamonds,

resembling in many ways the little black gems produced by Moissan’s

method with the aid of the electric furnace. The fact that they are

found embedded in these iron meteorites is another argument in favor of

the hypothesis of the solar or stellar origin of the latter. To

appreciate this it is necessary to recall the way in which Moissan made

his diamonds. It was by a combination of the effects of great heat,

great pressure, and sudden or rapid superficial cooling on a mass of

iron containing carbon. When he finally broke open his iron he found it

a pudding stuffed with miniature black diamonds. When a fragment of the

Canyon Diablo meteoric iron was polished in Philadelphia over fifteen

years ago it cut the emery-wheel to pieces, and examination showed that

the damage had been effected by microscopic diamonds peppered through

the mass. How were those diamonds formed? If the sun or Sirius was the

laboratory that prepared them, we can get a glimpse at the process of

their formation. There is plenty of heat, plenty of pressure, and an

abundance of vaporized iron in the sun and the stars. When a great

solar eruption takes place, masses of iron which have absorbed carbon

may be shot out with a velocity which forbids their return. Plunged

into the frightful cold of space, their surfaces are quickly cooled, as

Moissan cooled his prepared iron by throwing it into water, and thus

the requisite stress is set up within, and, as the iron solidifies, the

included carbon crystallizes into diamonds. Whether this explanation

has a germ of truth in it or not, at any rate it is evident that iron

meteorites were not created in the form in which they come to us; they

must once have been parts of immeasurably more massive bodies than

themselves.

The fall of meteorites offers an appreciable, though numerically

insignificant, peril to the inhabitants of the earth. Historical

records show perhaps three or four instances of people being killed by

these bodies. But for the protection afforded by the atmosphere, which

acts as a very effective shield, the danger would doubtless be very

much greater. In the absence of an atmosphere not only would more

meteorites reach the ground, but their striking force would be

incomparably greater, since, as we have seen, the larger part of their

original velocity is destroyed by the resistance of the air. A

meteorite weighing many tons and striking the earth with a velocity of

twenty or thirty miles per second, would probably cause frightful

havoc.

[Illustration: Looking across Coon Butte crater from northern rim]

It is a singular fact that recent investigations seem to have proved

that an event of this kind actually happened in North America—perhaps

not longer than a thousand or two thousand years ago. The scene of the

supposed catastrophe is in northern central Arizona, at Coon Butte,

where there is a nearly circular crater in the middle of a circular

elevation or small mountain. The crater is somewhat over four thousand

feet in diameter, and the surrounding rim, formed of upturned strata

and ejected rock fragments, rises at its highest point one hundred and

sixty feet above the plain. The crater is about six hundred feet in

depth—that is, from the rim to the visible floor or bottom of the

crater. There is no evidence that volcanic action has ever taken place

in the immediate neighborhood of Coon Butte. The rock in which the

crater has been made is composed of horizontal sandstone and limestone

strata. Between three hundred and four hundred million tons of rock

fragments have been detached, and a large portion hurled by some cause

out of the crater. These fragments lie concentrically distributed

around the crater, and in large measure form the elevation known as

Coon Butte. The region has been famous for nearly twenty years on

account of the masses of meteoric iron found scattered about and known

as the “Canyon Diablo” meteorites. It was one of these masses, which

consist of nickel-iron containing a small quantity of platinum, and of

which in all some ten tons have been recovered for sale to the various

collectors throughout the world, that as before mentioned destroyed the

grinding-tool at Philadelphia through the cutting power of its embedded

diamonds. These meteoric irons are scattered about the crater-hill, in

concentric distribution, to a maximum distance of about five miles.

When the suggestion was first made in 1896 that a monster meteorite

might have created by its fall this singular lone crater _in stratified

rocks,_ it was greeted with incredulous smiles; but since then the

matter has assumed a different aspect. The Standard Iron Company,

formed by Messrs. D. M. Barringer, B. C. Tilghman, E. J. Bennitt, and

S. J. Holsinger, having become, in 1903, the owner of this freak of

nature, sunk shafts and bored holes to a great depth in the interior of

the crater, and also trenched the slopes of the mountain, and the

result of their investigations has proved that the meteoric hypothesis

of origin is correct. (See the papers published in the _Proceedings of

the Academy of Natural Sciences of Philadelphia,_ December, 1905,

wherein it is proved that the United States Geological Survey was wrong

in believing this crater to have been due to a steam explosion. Since

that date there has been discovered a great amount of additional

confirmatory proof). Material of unmistakably meteoric origin was found

by means of the drills, mixed with crushed rock, to a depth of six

hundred to seven hundred feet below the floor of the crater, and a

great deal of it has been found admixed with the ejected rock fragments

on the outer slopes of the mountain, absolutely proving synchronism

between the two events, the formation of this great crater and the

falling of the meteoric iron out of the sky. The drill located in the

bottom of the crater was sent, in a number of cases, much deeper (over

one thousand feet) into unaltered horizontal red sandstone strata, but

no meteoric material was found below this depth (seven hundred feet, or

between eleven and twelve hundred feet below the level of the

surrounding plain), which has been assumed as being about the limit of

penetration. It is not possible to sink a shaft at present, owing to

the water which has drained into the crater, and which forms, with the

finely pulverized sandstone, a very troublesome quicksand encountered

at about two hundred feet below the visible floor of the crater. As

soon as this water is removed by pumping it will be easy to explore the

depths of the crater by means of shafts and drifts. The rock strata

(sandstone and limestone) of which the walls consist present every

appearance of having been violently upturned by a huge body penetrating

the earth like a cannon-ball. The general aspect of the crater

strikingly resembles the impression made by a steel projectile shot

into an armor-plate. Mr Tilghman has estimated that a meteorite about

five hundred feet in diameter and moving with a velocity of about five

miles per second would have made just such a perforation upon striking

rocks of the character of those found at this place. There was some

fusion of the colliding masses, and the heat produced some steam from

the small amount of water in the rocks. As a result there has been

found at depth a considerable amount of fused quartz (original

sandstone), and with it innumerable particles or sparks of fused

nickel-iron (original meteorite). A projectile of that size penetrating

eleven to twelve hundred feet into the rocky shell of the globe must

have produced a shock which was perceptible several hundred miles away.

[Illustration: Trail on south side, Coon Butte crater]

The great velocity ascribed to the supposed meteorite at the moment of

striking could be accounted for by the fact that it probably plunged

nearly vertically downward, for it formed a circular crater in the

rocky crust of the earth. In that case it would have been less retarded

by the resistance of the atmosphere than are meteorites which enter the

air at a lower angle and shoot ahead hundreds of miles until friction

has nearly destroyed their original motion when they drop upon the

earth. Some meteoric masses of great size, such as Peary’s iron

meteorite found at Cape York, Greenland, and the almost equally large

mass discovered at Bacubirito, Mexico, appear to have penetrated but

slightly on striking the earth. This may be explained by supposing that

they pursued a long, horizontal course through the air before falling.

The result would be that, their original velocity having been

practically destroyed, they would drop to the ground with a velocity

nearly corresponding to that which gravity would impart within the

perpendicular distance of their final fall. A

six-hundred-and-sixty-pound meteorite, which fell at Knyahinya,

Hungary, striking at an angle of 27° from the vertical, penetrated the

ground to a depth of eleven feet.

It has been remarked that the Coon Butte meteorite may have fallen not

longer ago than a few thousand years. This is based upon the fact that

the geological indications favor the supposition that the event did not

occur more than five thousand years ago, while on the other hand the

rings of growth in the cedar-trees growing on the slopes of the crater

show that they have existed there about seven hundred years. Prof.

William H. Pickering has recently correlated this with an ancient

chronicle which states that at Cairo, Egypt, in the year 1029, “many

stars passed with a great noise.” He remarks that Cairo is about 100°,

by great circle, from Coon Butte, so that if the meteorite that made

the crater was a member of a flock of similar bodies which encountered

the earth moving in parallel lines, some of them might have traversed

the sky tangent to the earth’s surface at Cairo. That the spectacle

spoken of in the chronicle was caused by meteorites he deems

exceedingly probable because of what is said about “a great noise;”

meteorites are the only celestial phenomena attended with perceptible

sounds. Professor Pickering conjectures that this supposed flock of

great meteorites may have formed the nucleus of a comet which struck

the earth, and he finds confirmation of the idea in the fact that out

of the ten largest meteorites known, no less than seven were found

within nine hundred miles of Coon Butte. It would be interesting if we

could trace back the history of that comet, and find out what malicious

planet caught it up in its innocent wanderings and hurled it with so

true an aim at the earth! This remarkable crater is one of the most

interesting places in the world, for there is absolutely no record of

such a mass, possibly an iron-headed comet, from outer space having

come into collision with our earth. The results of the future

exploration of the depths of the crater will be awaited with much

interest.

XII

The Wrecking of the Moon

There are sympathetic moods under whose influence one gazes with a

certain poignant tenderness at the worn face of the moon; that little

“fossil world” (the child of our mother earth, too) bears such terrible

scars of its brief convulsive life that a sense of pity is awakened by

the sight. The moon is the wonder-land of the telescope. Those towering

mountains, whose “proud aspiring peaks” cast silhouettes of shadow that

seem drawn with india-ink; those vast plains, enchained with gentle

winding hills and bordered with giant ranges; those oval “oceans,”

where one looks expectant for the flash of wind-whipped waves; those

enchanting “bays” and recesses at the seaward feet of the Alps; those

broad straits passing between guardian heights incomparably mightier

than Gibraltar; those locket-like valleys as secluded among their

mountains as the Vale of Cashmere; those colossal craters that make us

smile at the pretensions of Vesuvius, Etna, and Cotopaxi; those strange

white ways which pass with the unconcern of Roman roads across

mountain, gorge, and valley—all these give the beholder an irresistible

impression that it is truly a world into which he is looking, a world

akin to ours, and yet no more like our world than Pompeii is like

Naples. Its air, its waters, its clouds, its life are gone, and only a

skeleton remains—a mute but eloquent witness to a cosmical tragedy

without parallel in the range of human knowledge.

One cannot but regret that the moon, if it ever was the seat of

intelligent life, has not remained so until our time. Think what the

consequences would have been if this other world at our very door had

been found to be both habitable and inhabited! We talk rather airily of

communicating with Mars by signals; but Mars never approaches nearer

than 35,000,000 miles, while the moon when nearest is only a little

more than 220,000 miles away. Given an effective magnifying power of

five thousand diameters, which will perhaps be possible at the mountain

observatories as telescopes improve, and we should be able to bring the

moon within an apparent distance of about forty miles, while the

corresponding distance for Mars would be more than seven thousand

miles. But even with existing telescopic powers we can see details on

the moon no larger than some artificial constructions on the earth. St

Peter’s at Rome, with the Vatican palace and the great piazza, if

existing on the moon, would unquestionably be recognizable as something

else than a freak of nature. Large cities, with their radiating lines

of communication, would at once betray their real character. Cultivated

tracts, and the changes produced by the interference of intelligent

beings, would be clearly recognizable. The electric illumination of a

large town at night would probably be markedly visible. Gleams of

reflected sunlight would come to us from the surfaces of the lakes and

oceans, and a huge “liner” traversing a lunar sea could probably be

followed by its trail of smoke. As to communications by “wireless”

signals, which certain enthusiasts have thought of in connection with

Mars, in the case of the moon they should be a relatively simple

matter, and the feat might actually be accomplished. Think what a

literature would grow up about the moon if it were a living world! Its

very differences from the earth would only accentuate its interest for

us. Night and day on the moon are each two weeks in length; how

interesting it would be to watch the manner in which the lunarians

dealt with such a situation as that. Lunar and terrestrial history

would keep step with each other, and we should record them both. Truly

one might well wish to have a neighbor world to study; one would feel

so much the less alone in space.

It is not impossible that the moon did at one time have inhabitants of

some kind. But, if so, they vanished with the disappearance of its

atmosphere and seas, or with the advent of its cataclysmic age. At the

best, its career as a living world must have been brief. If the water

and air were gradually absorbed, as some have conjectured, by its

cooling interior rocks, its surface might, nevertheless, have retained

them for long ages; but if, as others think, their disappearance was

due to the escape of their gaseous molecules in consequence of the

inability of the relatively small lunar gravitation to retain them,

then the final catastrophe must have been as swift as it was

inevitable. Accepting Darwin’s hypothesis, that the moon was separated

from the earth by tidal action while both were yet plastic or nebulous,

we may reasonably conclude that it began its career with a good supply

of both water and air, but did not possess sufficient mass to hold them

permanently. Yet it may have retained them long enough for life to

develop in many forms upon its surface; in fact, there are so many

indications that air and water have not always been lacking to the

lunar world that we are driven to invent theories to explain both their

former presence and their present absence.

[Illustration: The craters Clavius, Longomontanus, Tycho, etc.]

But whatever the former condition of the moon may have been, its

existing appearance gives it a resistless fascination, and it bears so

clearly the story of a vast catastrophe sculptured on its rocky face

that the thoughtful observer cannot look upon it without a feeling of

awe. The gigantic character of the lunar features impresses the

beholder not less than the universality of the play of destructive

forces which they attest. Let us make a few comparisons. Take the lunar

crater called “Tycho”, which is a typical example of its kind. In the

telescope Tycho appears as a perfect ring surrounding a circular

depression, in the center of which rises a group of mountains. Its

superficial resemblance to some terrestrial volcanic craters is very

striking. Vesuvius, seen from a point vertically above, would no doubt

look something like that (the resemblance would have been greater when

the Monte del Cavallo formed a more complete circuit about the crater

cone). But compare the dimensions. The remains of the outer crater ring

of Vesuvius are perhaps half a mile in diameter, while the active

crater itself is only two or three hundred feet across at the most;

Tycho has a diameter of fifty-four miles! The group of relatively

insignificant peaks in the center of the crater floor of Tycho is far

more massive than the entire mountain that we call Vesuvius. The

largest known volcanic crater on the earth, Aso San, in Japan, has a

diameter of seven miles; it would take _sixty_ craters like Aso San to

equal Tycho in area! And Tycho, though one of the most perfect, is by

no means the largest crater on the moon. Another, called “Theophilus,”

has a diameter of sixty-four miles, and is eighteen thousand feet deep.

There are hundreds from ten to forty miles in diameter, and thousands

from one to ten miles. They are so numerous in many places that they

break into one another, like the cells of a crushed honeycomb.

The lunar craters differ from those of the earth more fundamentally

than in the matter of mere size; _they are not situated on the tops of

mountains._ If they were, and if all the proportions were the same, a

crater like Tycho might crown a conical peak fifty or one hundred miles

high! Instead of being cavities in the summits of mountains, the lunar

craters are rather gigantic sink-holes whose bottoms in many cases lie

two or three miles below the general surface of the lunar world. Around

their rims the rocks are piled up to a height of from a few hundred to

two or three thousand feet, with a comparatively gentle inclination,

but on the inner side they fall away in gigantic broken precipices

which make the dizzy cliffs of the Matterhorn seem but “lover’s leaps.”

Down they drop, ridge below ridge, crag under crag, tottering wall

beneath wall, until, in a crater named “Newton,” near the south lunar

pole, they attain a depth where the rays of the sun never reach.

Nothing more frightful than the spectacle which many of these terrible

chasms present can be pictured by the imagination. As the lazy lunar

day slowly advances, the sunshine, unmitigated by clouds or atmospheric

veil of any kind, creeps across their rims and begins to descend the

opposite walls. Presently it strikes the ragged crest of a ridge which

had lain hidden in such darkness as we never know on the earth, and

runs along it like a line of kindling fire. Rocky pinnacles and needles

shoot up into the sunlight out of the black depths. Down sinks the line

of light, mile after mile, and continually new precipices and cliffs

are brought into view, until at last the vast floor is attained and

begins to be illuminated. In the meanwhile the sun’s rays, darting

across the gulf, have touched the summits of the central peaks, twenty

or thirty miles from the crater’s inmost edge, and they immediately

kindle and blaze like huge stars amid the darkness. So profound are

some of these awful craters that days pass before the sun has risen

high enough above them to chase the last shadows from their depths.

Although several long ranges of mountains resembling those of the earth

exist on the moon, the great majority of its elevations assume the

crateriform aspect. Sometimes, instead of a crater, we find an immense

mountain ring whose form and aspect hardly suggest volcanic action. But

everywhere the true craters are in evidence, even on the sea-beds,

although they attain their greatest number and size on those parts of

the moon—covering sixty per cent of its visible surface—which are

distinctly mountainous in character and which constitute its most

brilliant portions. Broadly speaking, the southwestern half of the moon

is the most mountainous and broken, and the northeastern half the least

so. Right down through the center, from pole to pole, runs a wonderful

line of craters and crateriform valleys of a magnitude stupendous even

for the moon. Another similar line follows the western edge. Three or

four “seas” are thrust between these mountainous belts. By the effects

of “libration” parts of the opposite hemisphere of the moon which is

turned away from the earth are from time to time brought into view, and

their aspect indicates that that hemisphere resembles in its surface

features the one which faces the earth. There are many things about the

craters which seem to give some warrant for the hypothesis which has

been particularly urged by Mr G. K. Gilbert, that they were formed by

the impact of meteors; but there are also many things which militate

against that idea, and, upon the whole, the volcanic theory of their

origin is to be preferred.

The enormous size of the lunar volcanoes is not so difficult to account

for when we remember how slight is the force of lunar gravity as

compared with that of the earth. With equal size and density, bodies on

the moon weigh only one-sixth as much as on the earth. Impelled by the

same force, a projectile that would go ten miles on the earth would go

sixty miles on the moon. A lunar giant thirty-five feet tall would

weigh no more than an ordinary son of Adam weighs on his greater

planet. To shoot a body from the earth so that it would not drop back

again, we should have to start it with a velocity of seven miles per

second; a mile and a half per second would serve on the moon. It is by

no means difficult to believe, then, that a lunar volcano might form a

crater ring eight or ten times broader than the greatest to be found on

the earth, especially when we reflect that in addition to the

relatively slight force of gravity, the materials of the lunar crust

are probably lighter than those of our terrestrial rocks.

[Illustration: Western part of the Mare Serenitatis]

For similar reasons it seems not impossible that the theory mentioned

in a former chapter—that some of the meteorites that have fallen upon

the earth originated from the lunar volcanoes—is well founded. This

would apply especially to the stony meteorites, for it is hardly to be

supposed that the moon, at least in its superficial parts, contains

much iron. It is surely a scene most strange that is thus presented to

the mind’s eye—that little attendant of the earth’s (the moon has only

one-fiftieth of the volume, and only one-eightieth of the mass of the

earth) firing great stones back at its parent planet! And what can have

been the cause of this furious outbreak of volcanic forces on the moon?

Evidently it was but a passing stage in its history; it had enjoyed

more quiet times before. As it cooled down from the plastic state in

which it parted from the earth, it became incrusted after the normal

manner of a planet, and then oceans were formed, its atmosphere being

sufficiently dense to prevent the water from evaporating and the

would-be oceans from disappearing continually in mist. This, if any,

must have been the period of life in the lunar world. As we look upon

the vestiges of that ancient world buried in the wreck that now covers

so much of its surface, it is difficult to restrain the imagination

from picturing the scenes which were once presented there; and, in such

a case, should the imagination be fettered? We give it free rein in

terrestrial life, and it rewards us with some of our greatest

intellectual pleasures. The wonderful landscapes of the moon offer it

an ideal field with just enough half-hidden suggestions of facts to

stimulate its powers.

The great plains of the _Mare Imbrium_ and the _Mare Serenitatis_ (the

“Sea of Showers” and the “Sea of Serenity”), bordered in part by lofty

mountain ranges precisely like terrestrial mountains, scalloped along

their shores with beautiful bays curving back into the adjoining

highlands, and united by a great strait passing between the nearly

abutting ends of the “Lunar Apennines” and the “Lunar Caucasus,” offer

the elements of a scene of world beauty such as it would be difficult

to match upon our planet. Look at the finely modulated bottom of the

ancient sea in Mr Ritchey’s exquisite photograph of the western part of

the _Mare Serenitatis,_ where one seems to see the play of the watery

currents heaping the ocean sands in waving lines, making shallows,

bars, and deeps for the mariner to avoid or seek, and affording a

playground for the creatures of the main. What geologist would not wish

to try his hammer on those rocks with their stony pages of fossilized

history? There is in us an instinct which forbids us to think that

there was never any life there. If we could visit the moon, there is

not among us a person so prosaic and unimaginative that he would not,

the very first thing, begin to search for traces of its inhabitants. We

would look for them in the deposits on the sea bottoms; we would

examine the shores wherever the configuration seemed favorable for

harbors and the sites of maritime cities—forgetting that it may be a

little ridiculous to ascribe to the ancient lunarians the same ideas

that have governed the development of our race; we would search through

the valleys and along the seeming courses of vanished streams; we would

explore the mountains, not the terrible craters, but the pinnacled

chains that recall our own Alps and Rockies; seeking everywhere some

vestige of the transforming presence of intelligent life. Perhaps we

should find such traces, and perhaps, with all our searching, we should

find nothing to suggest that life had ever existed amid that universal

ruin.

[Illustration: Mare Tranquilitatis and surroundings]

Look again at the border of the “Sea of Serenity”—what a name for such

a scene!—and observe how it has been rent with almost inconceivable

violence, the wall of the colossal crater Posidonius dropping

vertically upon the ancient shore and obliterating it, while its giant

neighbor, Le Monnier, opens a yawning mouth as if to swallow the sea

itself. A scene like this makes one question whether, after all, those

may not be right who have imagined that the so-called sea bottoms are

really vast plains of frozen lava which gushed up in floods so

extensive that even the mighty volcanoes were half drowned in the fiery

sea. This suggestion becomes even stronger when we turn to another of

the photographs of Mr Ritchey’s wonderful series, showing a part of the

_Mare Tranquilitatis_ (“Sea of Tranquility”!). Notice how near the

center of the picture the outline of a huge ring with radiating ridges

shows through the sea bottom; a fossil volcano submerged in a petrified

ocean! This is by no means the only instance in which a buried world

shows itself under the great lunar plains. Yet, as the newer craters in

the sea itself prove, the volcanic activity survived this other

catastrophe, or broke out again subsequently, bringing more ruin to

pile upon ruin.

Yet notwithstanding the evidence which we have just been considering in

support of the hypothesis that the “seas” are lava floods, Messrs.

Loewy and Puiseux, the selenographers of the Paris Observatory, are

convinced that these great plains bear characteristic marks of the

former presence of immense bodies of water. In that case we should be

forced to conclude that the later oceans of the moon lay upon vast

sheets of solidified lava; and thus the catastrophe of the lunar world

assumes a double aspect, the earliest oceans being swallowed up in

molten floods issuing from the interior, while the lands were reduced

to chaos by a universal eruption of tremendous volcanoes; and then a

period of comparative quiet followed, during which new seas were

formed, and new life perhaps began to flourish in the lunar world, only

to end in another cataclysm, which finally put a term to the existence

of the moon as a life-supporting world.

Suppose we examine two more of Mr Ritchey’s illuminating photographs,

and, first, the one showing the crater Theophilus and its surroundings.

We have spoken of Theophilus before, citing the facts that it is

sixty-four miles in diameter and eighteen thousand feet deep. It will

be noticed that it has two brother giants—Cyrillus the nearer, and

Catharina the more distant; but Theophilus is plainly the youngest of

the trio. Centuries, and perhaps thousands of years, must have elapsed

between the periods of their upheaval, for the two older craters are

partly filled with débris, while it is manifest at a glance that when

the south eastern wall of Theophilus was formed, it broke away and

destroyed a part of the more ancient ring of Cyrillus. There is no more

tremendous scene on the moon than this; viewed with a powerful

telescope, it is absolutely appalling.

[Illustration: Lunar craters Theophilus and surrounding region]

The next photograph shows, if possible, a still wilder region. It is

the part of the moon lying between Tycho and the south pole. Tycho is

seen in the lower left-hand part of the picture. To the right, at the

edge of the illuminated portion of the moon, are the crater-rings,

Longomontanus and Wilhelm I, the former being the larger. Between them

are to be seen the ruins of two or three more ancient craters which,

together with portions of the walls of Wilhelm I and Longomontanus,

have been honeycombed with smaller craters. The vast crateriform

depression above the center of the picture is Clavius, an unrivaled

wonder of lunar scenery, a hundred and forty-two miles in its greatest

length, while its whole immense floor has sunk two miles below the

general surface of the moon outside the ring. The monstrous

shadow-filled cavity above Clavius toward the right is Blancanus, whose

aspect here gives a good idea of the appearance of these chasms when

only their rims are in the sunlight. But observe the indescribable

savagery of the entire scene. It looks as though the spirit of

destruction had gone mad in this spot. The mighty craters have broken

forth one after another, each rending its predecessor; and when their

work was finished, a minor but yet tremendous outbreak occurred, and

the face of the moon was gored and punctured with thousands of smaller

craters. These relatively small craters (small, however, only in a

lunar sense, for many of them would appear gigantic on the earth)

recall once more the theory of meteoric impact. It does not seem

impossible that some of them may have been formed by such an agency.

One would not wish for our planet such a fate as that which has

overtaken the moon, but we cannot be absolutely sure that something of

the kind may not be in store for it. We really know nothing of the

ultimate causes of volcanic activity, and some have suggested that the

internal energies of the earth may be accumulating instead of dying

out, and may never yet have exhibited their utmost destructive power.

Perhaps the best assurance that we can find that the earth will escape

the catastrophe that has overtaken its satellite is to be found in the

relatively great force of its gravitation. The moon has been the victim

of its weakness; given equal forces, and the earth would be the better

able to withstand them. It is significant, in connection with these

considerations, that the little planet Mercury, which seems also to

have parted with its air and water, shows to the telescope some

indications that it is pitted with craters resembling those that have

torn to pieces the face of the moon.

Upon the whole, after studying the dreadful lunar landscapes, one

cannot feel a very enthusiastic sympathy with those who are seeking

indications of the continued existence of some kind of life on the

moon; such a world is better without inhabitants. It has met its fate;

let it go! Fortunately, it is not so near that it cannot hide its scars

and appear beautiful—except when curiosity impels us to look with the

penetrating eyes of the astronomer.

[Illustration: Mare Crisium]

XIII

The Great Mars Problem

Let any thoughtful person who is acquainted with the general facts of

astronomy look up at the heavens some night when they appear in their

greatest splendor, and ask himself what is the strongest impression

that they make upon his mind. He may not find it easy to frame an

answer, but when he has succeeded it will probably be to the effect

that the stars give him an impression of the universality of

intelligence; they make him feel, as the sun and the moon cannot do,

that his world is not alone; that all this was not made simply to form

a gorgeous canopy over the tents of men. If he is of a devout turn of

mind, he thinks, as he gazes into those fathomless deeps and among

those bewildering hosts, of the infinite multitude of created beings

that the Almighty has taken under his care. The narrow ideas of the old

geocentric theology, which made the earth God’s especial footstool, and

man his only rational creature, fall away from him like a veil that had

obscured his vision; they are impossible in the presence of what he

sees above. Thus the natural tendency, in the light of modern progress,

is to regard the universe as everywhere filled with life.

But science, which is responsible for this broadening of men’s thoughts

concerning the universality of life, itself proceeds to set limits. Of

spiritual existences it pretends to know nothing, but as to physical

beings, it declares that it can only entertain the supposition of their

existence where it finds evidence of an environment suited to their

needs, and such environment may not everywhere exist. Science, though

repelled by the antiquated theological conception of the supreme

isolation of man among created beings, regards with complacency the

probability that there are regions in the universe where no organic

life exists, stars which shine upon no inhabited worlds, and planets

which nourish no animate creatures. The astronomical view of the

universe is that it consists of matter in every stage of evolution:

some nebulous and chaotic; some just condensing into stars (suns) of

every magnitude and order; some shaped into finished solar bodies

surrounded by dependent planets; some forming stars that perhaps have

no planets, and will have none; some constituting suns that are already

aging, and will soon lose their radiant energy and disappear; and some

aggregated into masses that long ago became inert, cold, and rayless,

and that can only be revivified by means about which we can form

conjectures, but of which we actually know nothing.

As with the stars, so with the planets, which are the satellites of

stars. All investigations unite to tell us that the planets are not all

in the same state of development. As some are large and some small, so

some are, in an evolutionary sense, young, and some old. As they depend

upon the suns around which they revolve for their light, heat, and

other forms of radiant energy, so their condition varies with their

distance from those suns. Many may never arrive at a state suitable for

the maintenance of life upon their surfaces; some which are not at

present in such a state may attain it later; and the forms of life

themselves may vary with the peculiar environment that different

planets afford. Thus we see that we are not scientifically justified in

affirming that life is ubiquitous, although we are thus justified in

saying that it must be, in a general sense, universal. We might liken

the universe to a garden known to contain every variety of plant. If on

entering it we see no flowers, we examine the species before us and

find that they are not of those which bloom at this particular season,

or perhaps they are such as never bear flowers. Yet we feel no doubt

that we shall find flowers somewhere in the garden, because there _are_

species which bloom at this season, and the garden contains _all_

varieties.

While it is tacitly assumed that there are planets revolving around

other stars than the sun, it would be impossible for us to see them

with any telescope yet invented, and no instrument now in the

possession of astronomers could assure us of their existence; so the

only planetary system of which we have visual knowledge is our own.

Excluding the asteroids, which could not from any point of view be

considered as habitable, we have in the solar system eight planets of

various sizes and situated at various distances from the sun. Of these

eight we know that one, the earth, is inhabited. The question, then,

arises: Are there any of the others which are inhabited or habitable?

Since it is our intention to discuss the habitability of only one of

the seven to which the question applies, the rest may be dismissed in a

few words. The smallest of them, and the nearest to the sun, is

Mercury, which is regarded as uninhabitable because it has no

perceptible supply of water and air, and because, owing to the

extraordinary eccentricity of its orbit, it is subjected to excessive

and very rapid alterations in the amount of solar heat and light poured

upon its surface, such alterations being inconsistent with the

supposition that it can support living beings. Even its average

temperature is more than six and a half times that prevailing on the

earth! Another circumstance which militates against its habitability is

that, according to the results of the best telescopic studies, it

always keeps the same face toward the sun, so that one half of the

planet is perpetually exposed to the fierce solar rays, and the other

half faces the unmitigated cold of open space. Venus, the next in

distance from the sun, is almost the exact twin of the earth in size,

and many arguments may be urged in favor of its habitability, although

it is suspected of possessing the same peculiarity as Mercury, in

always keeping the same side sunward. Unfortunately its atmosphere

appears to be so dense that no permanent markings on its surface are

certainly visible, and the question of its actual condition must, for

the present, be left in abeyance. Mars, the first planet more distant

from the sun than the earth, is the special subject of this chapter,

and will be described and discussed a few lines further on. Jupiter,

Saturn, Uranus, and Neptune, the four giant planets, all more distant

than Mars, and each more distant than the other in the order named, are

all regarded as uninhabitable because none of them appears to possess

any degree of solidity. They may have solid or liquid nuclei, but

exteriorly they seem to be mere balls of cloud. Of course, one can

imagine what he pleases about the existence of creatures suited to the

physical constitution of such planets as these, but they must be

excluded from the category of habitable worlds in the ordinary sense of

the term. We go back, then, to Mars.

It will be best to begin with a description of the planet. Mars is 4230

miles in diameter; its surface is not much more than one-quarter as

extensive as that of the earth (.285). Its mean distance from the sun

is 141,500,000 miles, 48,500,000 miles greater than that of the earth.

Since radiant energy varies inversely as the square of distance, Mars

receives less than half as much solar light and heat as the earth gets.

Mars’ year (period of revolution round the sun) is 687 days. Its mean

density is 71 per cent of the earth’s, and the force of gravity on its

surface is 38 per cent of that on the surface of the earth; _i.e.,_ a

body weighing one hundred pounds on the earth would, if transported to

Mars, weigh but thirty-eight pounds. The inclination of its equator to

the plane of its orbit differs very little from that of the earth’s

equator, and its axial rotation occupies 24 hours 37 minutes. so that

the length of day and night, and the extent of the seasonal changes on

Mars, are almost precisely the same as on the earth. But owing to the

greater length of its year, the seasons of Mars, while occurring in the

same order, are almost twice as long as ours. The surface of the planet

is manifestly solid, like that of our globe, and the telescope reveals

many permanent markings on it, recalling the appearance of a globe on

which geographical features have been represented in reddish and dusky

tints. Around the poles are plainly to be seen rounded white areas,

which vary in extent with the Martian seasons, nearly vanishing in

summer and extending widely in winter. The most recent spectroscopic

determinations indicate that Mars has an atmosphere perhaps as dense as

that to be found on our loftiest mountain peaks, and there is a

perceptible amount of watery vapor in this atmosphere. The surface of

the planet appears to be remarkably level, and it has no mountain

ranges. No evidences of volcanic action have been discovered on Mars.

The dusky and reddish areas were regarded by the early observers as

respectively seas and lands, but at present it is not believed that

there are any bodies of water on the planet. There has never been much

doubt expressed that the white areas about the poles represent snow.

It will be seen from this brief description that many remarkable

resemblances exist between Mars and the earth, and there is nothing

wonderful in the fact that the question of the habitability of the

former has become one of extreme and wide-spread interest, giving rise

to the most diverse views, to many extraordinary speculations, and

sometimes to regrettably heated controversy. The first champion of the

habitability of Mars was Sir William Herschel, although even before his

time the idea had been suggested. He was convinced by the revelations

of his telescopes, continually increasing in power, that Mars was more

like the earth than any other planet. He could not resist the testimony

of the polar snows, whose suggestive conduct was in such striking

accord with what occurs upon the earth. Gradually, as telescopes

improved and observers increased in number, the principal features of

the planet were disclosed and charted, and “areography,” as the

geography of Mars was called, took its place among the recognized

branches of astronomical study. But it was not before 1877 that a

fundamentally new discovery in areography gave a truly sensational turn

to speculation about life on “the red planet.” In that year Mars made

one of its nearest approaches to the earth, and was so situated in its

orbit that it could be observed to great advantage from the northern

hemisphere of the earth. The celebrated Italian astronomer,

Schiaparelli, took advantage of this opportunity to make a

trigonometrical survey of the surface of Mars—as coolly and confidently

as if he were not taking his sights across a thirty-five-million-mile

gulf of empty space—and in the course of this survey he was astonished

to perceive that the reddish areas, then called continents, were

crossed in many directions by narrow, dusky lines, to which he gave the

suggestive name of “canals.” Thus a kind of firebrand was cast into the

field of astronomical speculation, which has ever since produced

disputes that have sometimes approached the violence of political

faction. At first the accuracy of Schiaparelli’s observations was

contested; it required a powerful telescope, and the most excellent

“seeing,” to render the enigmatical lines visible at all, and many

searchers were unable to detect them. But Schiaparelli continued his

studies in the serene sky of Italy, and produced charts of the

gridironed face of Mars containing so much astonishing detail that one

had either to reject them _in toto_ or to confess that Schiaparelli was

right. As subsequent favorable oppositions of Mars occurred, other

observers began to see the “canals” and to confirm the substantial

accuracy of the Italian astronomer’s work, and finally few were found

who would venture to affirm that the “canals” did not exist, whatever

their meaning might be.

[Illustration: Schiaparelli’s chart of Mars, showing the so-called

system of canals]

When Schiaparelli began his observations it was generally believed, as

we have said, that the dusky areas on Mars were seas, and since

Schiaparelli thought that the “canals” invariably began and ended at

the shores of the “seas,” the appropriateness of the title given to the

lines seemed apparent. Their artificial character was immediately

assumed by many, because they were too straight and too suggestively

geometrical in their arrangement to permit the conclusion that they

were natural watercourses. A most surprising circumstance noted by

Schiaparelli was that the “canals” made their appearance _after_ the

melting of the polar snow in the corresponding hemisphere had begun,

and that they grew darker, longer, and more numerous in proportion as

the polar liquidation proceeded; another very puzzling observation was

that many of them became double as the season advanced; close beside an

already existing “canal,” and in perfect parallelism with it, another

would gradually make its appearance. That these phenomena actually

existed and were not illusions was proved by later observations, and

today they are seen whenever Mars is favorably situated for

observation.

In the closing decade of the nineteenth century, Mr Percival Lowell

took up the work where Schiaparelli had virtually dropped it, and soon

added a great number of “canals” to those previously known, so that in

his charts the surface of the wonderful little planet appears covered

as with a spider’s web, the dusky lines criss-crossing in every

direction, with conspicuous knots wherever a number of them come

together. Mr Lowell has demonstrated that the areas originally called

seas, and thus named on the earlier charts, are not bodies of water,

whatever else they may be. He has also found that the mysterious lines

do not, as Schiaparelli supposed, begin and end at the edges of the

dusky regions, but often continue on across them, reaching in some

cases far up into the polar regions. But Schiaparelli was right in his

observation that the appearance of the “canals” is synchronous with the

gradual disappearance of the polar snows, and this fact has become the

basis of the most extraordinary theory that the subject of life in

other worlds has ever given birth to.

Now, the effect of such discoveries, as we have related, depends upon

the type of mind to whose attention they are called. Many are content

to accept them as strange and inexplicable at present, and to wait for

further light upon them; others insist upon an immediate inquiry

concerning their probable nature and meaning. Such an inquiry can only

be based upon inference proceeding from analogy. Mars, say Mr Lowell

and those who are of his opinion, is manifestly a solidly incrusted

planet like the earth; it has an atmosphere, though one of great

rarity; it has water vapor, as the snows in themselves prove; it has

the alternation of day and night, and a succession of seasons closely

resembling those of the earth; its surface is suggestively divided into

regions of contrasting colors and appearance, and upon that surface we

see an immense number of lines geometrically arranged, with a system of

symmetrical intersections where the lines expand into circular and oval

areas—and all connected with the annual melting of the polar snows in a

way which irresistibly suggests the interference of intelligence

directed to a definite end. Why, with so many concurrent circumstances

to support the hypothesis, should we not regard Mars as an inhabited

globe?

But the differences between Mars and the earth are in many ways as

striking as their resemblances. Mars is relatively small; it gets less

than half as much light and heat as we receive; its atmosphere is so

rare that it would be distressing to us, even if we could survive in it

at all; it has no lakes, rivers, or seas; its surface is an endless

prairie. and its “canals” are phenomena utterly unlike anything on the

earth. Yet it is precisely upon these divergences between the earth and

Mars, this repudiation of terrestrial standards, that the theory of

“life on Mars,” for which Mr Lowell is mainly responsible, is based.

Because Mars is smaller than the earth, we are told it must necessarily

be more advanced in planetary evolution, the underlying cause of which

is the gradual cooling and contraction of the planet’s mass. Mars has

parted with its internal heat more rapidly than the earth; consequently

its waters and its atmosphere have been mostly withdrawn by chemical

combinations, but enough of both yet remain to render life still

possible on its surface. As the globe of Mars is evolutionally older

than that of the earth, so its forms of organic life may be

proportionally further advanced, and its inhabitants may have attained

a degree of cultivated intelligence much superior to what at present

exists upon the earth. Understanding the nature and the causes of the

desiccation of their planet, and possessing engineering science and

capabilities far in advance of ours, they may be conceived to have

grappled with the stupendous problem of keeping their world in a

habitable condition as long as possible. Supposing them to have become

accustomed to live in their rarefied atmosphere (a thing not

inconceivable, since men can live for a time at least in air hardly

less rare), the most pressing problem for them is that of a

water-supply, without which plant life cannot exist, while animal life

in turn depends for its existence upon vegetation. The only direction

in which they can seek water is that of the polar regions, where it is

alternately condensed into snow and released in the liquid form by the

effect of the seasonal changes. It is, then, to the annual melting of

the polar snow-fields that the Martian engineers are supposed to have

recourse in supplying the needs of their planet, and thus providing the

means of prolonging their own existence. It is imagined that they have

for this purpose constructed a stupendous system of irrigation

extending over the temperate and equatorial regions of the planet. The

“canals” represent the lines of irrigation, but the narrow streaks that

we see are not the canals themselves, but the irrigated bands covered

by them. Their dark hue, and their gradual appearance after the polar

melting has begun, are due to the growth of vegetation stimulated by

the water. The rounded areas visible where several “canals” meet and

cross are called by Mr Lowell “oases.” These are supposed to be the

principal centers of population and industry. It must be confessed that

some of them, with their complicated systems of radiating lines, appear

to answer very well to such a theory. No attempt to explain them by

analogy with natural phenomena on the earth has proved successful.

But a great difficulty yet remains: How to explain the seemingly

miraculous powers of the supposed engineers? Here recourse is had once

more to the relative smallness of the planet. We have remarked that the

force of gravity on Mars is only thirty-eight per cent of that on the

earth. A steam-shovel driven by a certain horse-power would be nearly

three times as effective there as here. A man of our stature on Mars

would find his effective strength increased in the same proportion. But

just because of the slight force of gravity there, a Martian might

attain to the traditional stature of Goliath without finding his own

weight an encumbrance to his activity, while at the same time his huge

muscles would come into unimpeded play, enabling him single-handed to

perform labors that would be impossible to a whole gang of terrestrial

workmen. The effective powers of huge machines would be increased in

the same way; and to all this must be added the fact that the mean

density of the materials of which Mars is composed is much less than

that of the constituents of the earth. Combining all these

considerations, it becomes much less difficult to conceive that public

works might be successfully undertaken on Mars which would be

hopelessly beyond the limits of human accomplishment.

Certain other difficulties have also to be met; as, for instance, the

relative coldness of the climate of Mars. At its distance it gets

considerably less than half as much light and heat as we receive. In

addition to this, the rarity of its atmosphere would naturally be

expected to decrease the effective temperature at the planet’s surface,

since an atmosphere acts somewhat like the glass cover of a hot-house

in retaining the solar heat which has penetrated it. It has been

calculated that, unless there are mitigating circumstances of which we

know nothing, the average temperature at the surface of Mars must be

far below the freezing-point of water. To this it is replied that the

possible mitigating circumstances spoken of evidently exist in fact,

because we can _see_ that the watery vapor condenses into snow around

the poles in winter, but melts again when summer comes. The mitigating

agent may be supposed to exist in the atmosphere where the presence of

certain gases would completely alter the temperature gradients.

It might also be objected that it is inconceivable that the Martian

engineers, however great may be their physical powers, and however

gigantic the mechanical energies under their control, could force water

in large quantities from the poles to the equator. This is an

achievement that measures up to the cosmical standard. It is admitted

by the champions of the theory that the difficulty is a formidable one;

but they call attention to the singular fact that on Mars there can be

found no chains of mountains, and it is even doubtful if ranges of

hills exist there. The entire surface of the planet appears to be

almost “as smooth as a billiard ball,” and even the broad regions which

were once supposed to be seas apparently lie at practically the same

level as the other parts, since the “canals” in many cases run

uninterruptedly across them. Lowell’s idea is that these sombre areas

may be expanses of vegetation covering ground of a more or less marshy

character, for while the largest of them appear to be permanent, there

are some which vary coincidently with the variations of the canals.

As to the kind of machinery employed to force the water from the poles,

it has been conjectured that it may have taken the form of a gigantic

system of pumps and conduits; and since the Martians are assumed to be

so far in advance of us in their mastery of scientific principles, the

hypothesis will at least not be harmed by supposing that they have

learned to harness forces of nature whose very existence in a

manageable form is yet unrecognized on the earth. If we wish to let the

imagination loose, we may conjecture that they have conquered the

secret of those intra-atomic forces whose resistless energy is

beginning to become evident to us, but the possibility of whose

utilization remains a dream, the fulfillment of which nobody dares to

predict.

Such, in very brief form, is the celebrated theory of Mars as an

inhabited world. It certainly captivates the imagination, and if we

believe it to represent the facts, we cannot but watch with the deepest

sympathy this gallant struggle of an intellectual race to preserve its

planet from the effects of advancing age and death. We may, indeed,

wonder whether our own humanity, confronted by such a calamity, could

be counted on to meet the emergency with equal stoutness of heart and

inexhaustibleness of resource. Up to the present time we certainly have

shown no capacity to confront Nature toe to toe, and to seize her by

the shoulders and turn her round when she refuses to go our way. If we

could get into wireless telephonic communication with the Martians we

might learn from their own lips the secret of their more than “Roman

recovery.”

XIV

The Riddle of the Asteroids

Between the orbits of Mars and Jupiter revolves the most remarkable

system of little bodies with which we are acquainted—the Asteroids, or

Minor Planets. Some six hundred are now known, and they may actually

number thousands. They form virtually a ring about the sun. The most

striking general fact about them is that they occupy the place in the

sky which should be occupied, according to Bode’s Law, by a single

large planet. This fact, as we shall see, has led to the invention of

one of the most extraordinary theories in astronomy—_viz.,_ that of the

explosion of a world!

Bode’s Law, so-called, is only an empiric formula, but until the

discovery of Neptune it accorded so well with the distances of the

planets that astronomers were disposed to look upon it as really

representing some underlying principle of planetary distribution. They

were puzzled by the absence of a planet in the space between Mars and

Jupiter, where the “law” demanded that there should be one, and an

association of astronomers was formed to search for it. There was a

decided sensation when, in 1801, Piazzi, of Palermo, announced that he

had found a little planet which apparently occupied the place in the

system which belonged to the missing body. He named it Ceres, and it

was the first of the Asteroids. The next year Olbers, of Bremen, while

looking for Ceres with his telescope, stumbled upon another small

planet which he named Pallas. Immediately he was inspired with the idea

that these two planets were fragments of a larger one which had

formerly occupied the vacant place in the planetary ranks, and he

predicted that others would be found by searching in the neighborhood

of the intersection of the orbits of the two already discovered. This

bold prediction was brilliantly fulfilled by the finding of two

more—Juno in 1804, and Vesta in 1807. Olbers would seem to have been

led to the invention of his hypothesis of a planetary explosion by the

faith which astronomers at that time had in Bode’s Law. They appear to

have thought that several planets revolving in the gap where the “law”

called for but one could only be accounted for upon the theory that the

original _one_ had been broken up to form the several. Gravitation

demanded that the remnants of a planet blown to pieces, no matter how

their orbits might otherwise differ, should all return at stated

periods to the point where the explosion had occurred; hence Olbers’

prediction that any asteroids that might subsequently be discovered

would be found to have a common point of orbital intersection. And

curiously enough all of the first asteroids found practically answered

to this requirement. Olbers’ theory seemed to be established.

After the first four, no more asteroids were found until 1845, when one

was discovered; then, in 1847, three more were added to the list; and

after that searchers began to pick them up with such rapidity that by

the close of the century hundreds were known, and it had become almost

impossible to keep track of them. The first four are by far the largest

members of the group, but their actual sizes remained unknown until

less than twenty years ago. It was long supposed that Vesta was the

largest, because it shines more brightly than any of the others; but

finally, in 1895, Barnard, with the Lick telescope, definitely measured

their diameters, and proved to everybody’s surprise that Ceres is

really the chief, and Vesta only the third in rank. His measures are as

follows: Ceres, 477 miles; Pallas, 304 miles; Vesta, 239 miles; and

Juno, 120 miles. They differ greatly in the reflective power of their

surfaces, a fact of much significance in connection with the question

of their origin. Vesta is, surface for surface, rather more than three

times as brilliant as Ceres, whence the original mistake about its

magnitude.

Nowadays new asteroids are found frequently by photography, but

physically they are most insignificant bodies, their average diameter

probably not exceeding twenty miles, and some are believed not to

exceed ten. On a planet only ten miles in diameter, assuming the same

mean density as the earth’s, which is undoubtedly too much, the force

of gravity would be so slight that an average man would not weigh more

than three ounces, and could jump off into space whenever he liked.

Although the asteroids all revolve around the sun in the same direction

as that pursued by the major planets, their orbits are inclined at a

great variety of angles to the general plane of the planetary system,

and some of them are very eccentric—almost as much so as the orbits of

many of the periodic comets. It has even been conjectured that the two

tiny moons of Mars and the four smaller satellites of Jupiter may be

asteroids gone astray and captured by those planets. Two of the

asteroids are exceedingly remarkable for the shapes and positions of

their orbits; these are Eros, discovered in 1898, and T. G., 1906,

found eight years later. The latter has a mean distance from the sun

slightly greater than that of Jupiter, while the mean distance of Eros

is less than that of Mars. The orbit of Eros is so eccentric that at

times it approaches within 15,000,000 miles of the earth, nearer than

any other regular member of the solar system except the moon, thus

affording an unrivaled means of measuring the solar parallax. But for

our present purpose the chief interest of Eros lies in its

extraordinary changes of light.

These changes, although irregular, have been observed and photographed

many times, and there seems to be no doubt of their reality. Their

significance consists in their possible connection with the form of the

little planet, whose diameter is generally estimated at not more than

twenty miles. Von Oppolzer found, in 1901, that Eros lost three-fourths

of its brilliancy once in every two hours and thirty-eight minutes.

Other observers have found slightly different periods of variability,

but none as long as three hours. The most interesting interpretation

that has been offered of this phenomenon is that it is due to a great

irregularity of figure, recalling at once Olbers’ hypothesis. According

to some, Eros may be double, the two bodies composing it revolving

around each other at very close quarters; but a more striking, and it

may be said probable, suggestion is that Eros has a form not unlike

that of a dumb-bell, or hour-glass, turning rapidly end over end so

that the area of illuminated surface presented to our eyes continually

changes, reaching at certain times a minimum when the amount of light

that it reflects toward the earth is reduced to a quarter of its

maximum value. Various other bizarre shapes have been ascribed to Eros,

such, for instance, as that of a flat stone revolving about one of its

longer axes, so that sometimes we see its face and sometimes its edge.

All of these explanations proceed upon the assumption that Eros cannot

have a simple globular figure like that of a typical planet, a figure

which is prescribed by the law of gravitation, but that its shape is

what may be called accidental; in a word, it is a _fragment,_ for it

seems impossible to believe that a body formed in interplanetary space,

either through nebular condensation or through the aggregation of

particles drawn together by their mutual attractions, should not be

practically spherical in shape. Nor is Eros the only asteroid that

gives evidence by variations of brilliancy that there is something

abnormal in its constitution; several others present the same

phenomenon in varying degrees. Even Vesta was regarded by Olbers as

sufficiently variable in its light to warrant the conclusion that it

was an angular mass instead of a globe. Some of the smaller ones show

very notable variations, and all in short periods, of three or four

hours, suggesting that in turning about one of their axes they present

a surface of variable extent toward the sun and the earth.

The theory which some have preferred—that the variability of light is

due to the differences of reflective power on different parts of the

surface—would, if accepted, be hardly less suggestive of the origin of

these little bodies by the breaking up of a larger one, because the

most natural explanation of such differences would seem to be that they

arose from variations in the roughness or smoothness of the reflecting

surface, which would be characteristic of fragmentary bodies. In the

case of a large planet alternating expanses of land and water, or of

vegetation and desert, would produce a notable variation in the amount

of reflection, but on bodies of the size of the asteroids neither water

nor vegetation could exist, and an atmosphere would be equally

impossible.

One of the strongest objections to Olbers’ hypothesis is that only a

few of the first asteroids discovered travel in orbits which measurably

satisfy the requirement that they should all intersect at the point

where the explosion occurred. To this it was at first replied that the

perturbations of the asteroidal orbits, by the attractions of the major

planets, would soon displace them in such a manner that they would

cease to intersect. One of the first investigations undertaken by the

late Prof. Simon Newcomb was directed to the solution of this question,

and he arrived at the conclusion that the planetary perturbations could

not explain the actual situation of the asteroidal orbits. But

afterward it was pointed out that the difficulty could be avoided by

supposing that not one but a series of explosions had produced the

asteroids as they now are. After the primary disruption the fragments

themselves, according to this suggestion, may have exploded, and then

the resulting orbits would be as “tangled” as the heart could wish.

This has so far rehabilitated the explosion theory that it has never

been entirely abandoned, and the evidence which we have just cited of

the probably abnormal shapes of Eros and other asteroids has lately

given it renewed life. It is a subject that needs a thorough

rediscussion.

We must not fail to mention, however, that there is a rival hypothesis

which commends itself to many astronomers—_viz.,_ that the asteroids

were formed out of a relatively scant ring of matter, situated between

Mars and Jupiter and resembling in composition the immensely more

massive rings from which, according to Laplace’s hypothesis, the

planets were born. It is held by the supporters of this theory that the

attraction of the giant Jupiter was sufficient to prevent the small,

nebulous ring that gave birth to the asteroids from condensing like the

others into a single planet.

But if we accept the explosion theory, with its corollary that minor

explosions followed the principal one, we have still an unanswered

question before us: What caused the explosions? The idea of _a world

blowing up_ is too Titanic to be shocking; it rather amuses the

imagination than seriously impresses it; in a word, it seems

essentially chimerical. We can by no appeal to experience form a mental

picture of such an occurrence. Even the moon did not blow up when it

was wrecked by volcanoes. The explosive nebulæ and new stars are far

away in space, and suggest no connection with such a catastrophe as the

bursting of a planet into hundreds of pieces. We cannot conceive of a

great globe thousands of miles in diameter resembling a pellet of

gunpowder only awaiting the touch of a match to cause its sudden

disruption. Somehow the thought of human agency obtrudes itself in

connection with the word “explosion,” and we smile at the idea that

giant powder or nitro-glycerine could blow up a planet. Yet it would

only need _enough_ of them to do it.

After all, we may deceive ourselves in thinking, as we are apt to do,

that explosive energies lock themselves up only in small masses of

matter. There are many causes producing explosions in nature, every

volcanic eruption manifests the activity of some of them. Think of the

giant power of confined steam; if enough steam could be suddenly

generated in the center of the earth by a downpour of all the waters of

the oceans, what might not the consequences be for our globe? In a

smaller globe, and it has never been estimated that the original

asteroid was even as large as the moon, such a catastrophe would,

perhaps, be more easily conceivable; but since we are compelled in this

case to assume that there was a series of successive explosions, steam

would hardly answer the purpose; it would be more reasonable to suppose

that the cause of the explosion was some kind of chemical reaction, or

something affecting the atoms composing the exploding body. Here Dr

Gustav Le Bon comes to our aid with a most startling suggestion, based

on his theory of the dissipation of intra-atomic energy. It will be

best to quote him at some length from his book on _The Evolution of

Forces._

“It does not seem at first sight,” says Doctor Le Bon,

very comprehensible that worlds which appear more and more stable as

they cool could become so unstable as to afterward dissociate entirely.

To explain this phenomenon, we will inquire whether astronomical

observations do not allow us to witness this dissociation.

We know that the stability of a body in motion, such as a top or a

bicycle, ceases to be possible when its velocity of rotation descends

below a certain limit. Once this limit is reached it loses its

stability and falls to the ground. Prof. J. J. Thomson even interprets

radio-activity in this manner, and points out that when the speed of

the elements composing the atoms descends below a certain limit they

become unstable and tend to lose their equilibria. There would result

from this a commencement of dissociation, with diminution of their

potential energy and a corresponding increase of their kinetic energy

sufficient to launch into space the products of intra-atomic

disintegration.

It must not be forgotten that the atom being an enormous reservoir of

energy is by this very fact comparable with explosive bodies. These

last remain inert so long as their internal equilibria are undisturbed.

So soon as some cause or other modifies these, they explode and smash

everything around them after being themselves broken to pieces.

Atoms, therefore, which grow old in consequence of the diminution of a

part of their intra-atomic energy gradually lose their stability. A

moment, then, arrives when this stability is so weak that the matter

disappears by a sort of explosion more or less rapid. The bodies of the

radium group offer an image of this phenomenon—a rather faint image,

however, because the atoms of this body have only reached a period of

instability when the dissociation is rather slow. It probably precedes

another and more rapid period of dissociation capable of producing

their final explosion. Bodies such as radium, thorium, etc., represent,

no doubt, a state of old age at which all bodies must some day arrive,

and which they already begin to manifest in our universe, since all

matter is slightly radio-active. It would suffice for the dissociation

to be fairly general and fairly rapid for an explosion to occur in a

world where it was manifested.

These theoretical considerations find a solid support in the sudden

appearances and disappearances of stars. The explosions of a world

which produce them reveal to us, perhaps, how the universes perish when

they become old.

As astronomical observations show the relative frequency of these rapid

destructions, we may ask ourselves whether the end of a universe by a

sudden explosion after a long period of old age does not represent its

most general ending.

Here, perhaps, it will be well to stop, since, entrancing as the

subject may be, we know very little about it, and Doctor Le Bon’s

theory affords a limitless field for the reader’s imagination.