第 13 页

stretches away from the sun, because near by it is overwhelmed by

the more powerful light; in fact, I suspect it is principally in

the comet's shadow that the tail is visible. It is strange that

no one ever thought of that before, or that any one feared the

earth's passing through the tail of a comet. It is obvious to me

now that if there were any material substance, any gas, however

rarefied, in this hairlike[1] accompaniment, it would immediately

fall to the comparatively heavy head,

and surround that as a centre."

[1] Comet means literally a hair.

"How, then," asked Cortlandt, "do you account for the spaces

between those stones? However slight gravitation might be

between some of the grains, if it existed at all, or was

unopposed by some other force, with sufficient time--and they

have eternity--every comet would come together like a planet into

one solid mass. Perhaps some similar force maintains gases in

the distended tail, though I know of no such, or even any

analogous manifestation on earth. If the law on which we have

been brought up, that 'every atom in the universe attracts every

other atom,' were without exceptions or modifications, that comet

could not continue to exist in its present form. Until we get

some additional illustration, however, we shall be short of data

with which to formulate any iconoclastic hypothesis. The source

of the light, I must admit, also puzzles me greatly. There is

certainly no heat to which we can attribute it."

Having gone beyond the fragments, they applied a strong repulsion

charge to the comet, creating thereby a perfect whirlpool among

its particles, and quickly left it. Half an hour later they

again shut off the current, as the Callisto's speed was

sufficient.

For some time they had been in the belt of asteroids, but as yet

they had seen none near. The morning following their experience

with the comet, however, they went to their observatory after

breakfast as usual, and, on pointing their glasses forward,

espied a comparatively large body before them, a little to their

right.

"That must be Pallas," said Cortlandt, scrutinizing it closely.

"It was discovered by Olbers, in 1802, and was the second

asteroid found, Ceres having been the first, in 1801. It has a

diameter of about three hundred miles, being one of the largest

of these small planets. The most wonderful thing about it is the

inclination of its orbit--thirty-five degrees--to the plane of

the ecliptic; which means that at each revolution in its orbit,

it swings that much above and below the imaginary plane cutting

the sun at its equator, from which the earth and other larger

planets vary but little. This no doubt is due to the near

approach and disturbing attraction of some large comet, or else

it was flung above or below the ordinary plane in the catastrophe

that we think befell the large planet that doubtless formerly

existed where we now find this swarm. You can see that its path

makes a considerable angle to the plane of the ecliptic, and that

it is now about crossing the line."

It soon presented the phase of a half moon, but the waviness of

the straight line, as in the case of Venus and Mercury, showed

that the size of the mountains must be tremendous compared with

the mass of the body, some of them being obviously fifteen miles

high. The intense blackness of the shadows, as on the moon,

convinced them there was no trace of atmosphere.

"There being no air," said Cortlandt, "it is safe to assume there

is no water, which helps to account for the great inequalities on

the body's surface, since the mountains will seem higher when

surrounded by dry ocean- bottom than they would if water came

halfway up their sides. Undoubtedly, however, the main cause of

their height is the slight effect of gravitation on an asteroid,

and the fact that the shrinking of the interior, and consequent

folding of the crust in ridges, may have continued for a time

after there was no longer water on the surface to cut them down.

"The temperature and condition of a body," continued Cortlandt,

"seem to depend entirely on its size. In the sun we have an

incandescent, gaseous star, though its spots and the colour of

its rays show that it is becoming aged, or, to be more accurate,

advanced in its evolutionary development. Then comes a great

jump, for Jupiter has but about one fourteen-hundredth of the

mass of the sun, and we expect to find on it a firm crust, and

that the planet itself is at about the fourth or fifth period of

development, described by Moses as days. Saturn is doubtless

somewhat more advanced. The earth we know has been habitable

many hundreds of thousands or millions of years, though three

fourths of its surface is still covered by water. In Mars we see

a further step, three fourths of its surface being land. In

Mercury, could we study it better, or in the larger satellites of

Jupiter or Saturn, we might find a stepping-stone from Mars to

the moon, perhaps with no water, but still having air, and being

habitable in all other respects. In our own satellite we see a

world that has died, though its death from an astronomical point

of view is comparatively recent, while this little Pallas has

been dead longer, being probably chilled through and through.

From this I conclude that all bodies in the solar system had one

genesis, and were part of the same nebulous mass. But this does

not include the other systems and nebulae; for, compared with

them, our sun, as we have seen, is itself advanced and small

beside such stars as Sirius having diameters of twelve million

miles."

As they left Pallas between themselves and the sun, it became a

crescent and finally disappeared.

Two days later they sighted another asteroid exactly ahead. They

examined it closely, and concluded it must be Hilda, put down in

the astronomies as No. 153, and having almost the greatest mean

distance of any of these small bodies from the sun.

When they were so near that the disk was plainly visible to the

unaided eye, Hilda passed between them and Jupiter, eclipsing it.

To their surprise, the light was not instantly shut off, as when

the moon occults a star, but there was evident refraction.

"By George!" said Bearwarden, "here is an asteroid that HAS an

atmosphere."

There was no mistaking it. They soon discovered a small ice-cap

at one pole, and then made out oceans and continents, with

mountains, forests, rivers, and green fields. The sight lasted

but a few moments before they swept by, but they secured several

photographs, and carried a vivid impression in their minds.

Hilda appeared to be about two hundred miles in diameter.

"How do you account for that living world," Bearwarden asked

Cortlandt, "on your theory of size and longevity?"

"There are two explanations," replied Cortlandt, "if the theory,

as I still believe, is correct. Hilda has either been brought to

this system from some other less matured, in the train of a

comet, and been captured by the immense power of "Jupiter, which

might account for the eccentricity of its orbit, or some accident

has happened to rejuvenate it here. A collision with another

minor planet moving in an orbit that crossed its own, or with the

head of a large comet, would have reconverted it into a star,

perhaps after it had long been cold. A comet may first have so

changed the course of one of two small bodies as to make them

collide. This seems to me the most plausible theory. Over a

hundred years ago the English astronomer, Chambers, wrote of

having found traces of atmosphere in some of these minor planets,

but it was generally thought he was mistaken. One reason we know

so little about this great swarm of minor planets is, that till

recently none of them showed a disk to the telescope. Inasmuch

as only their light was visible, they were indistinguishable from

stars, except by their slow motion. A hundred years ago only

three hundred and fifty had been discovered; our photographic

star-charts have since then shown the number recorded to exceed

one thousand."

CHAPTER IV.

PREPARING TO ALIGHT.

That afternoon Ayrault brought out some statistical tables he had

compiled from a great number of books, and also a diagram of the

comparative sizes of the planets. "I have been not a little

puzzled at the discrepancies between even the best authors," he

said, "scarcely any two being exactly alike, while every decade

has seen accepted theories radically changed." Saying which, he

spread out the result of his labours (shown on the following

pages), which the three friends then studied.

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(1) Mean distance from sun in millions of miles

(2) Semimajor axis of orbit, earth's distance as 1

(3) Eccentricity of orbit

(4) Planets inclination of orbit to elliptic

(5) Light at perihelion

(6) Light at apehelion

(7) Heat, earth as 1

(1) (2) (3) (4) (5) (6) (7)

Mercury... 36.0 0.387 0.2056 7@0'8" 10.58 4.59 6.67

Venus..... 67.2 0.723 0.0068 3@23'35" 1.94 1.91 1.91

The Earth. 92.9 1.000 0.068 0@0'0" 1.03 0.997 1.00

Mars......141.5 1.524 0.0933 1@51'2" 0.52 0.360 1.43

Asteroids 204.4 to 2.200 0.4 to 5@-35@ 325.2 to 3.500 0.34

Jupiter.. 483.3 5.203 0.0483 1@18'41" 0.04 0.034 0.037

Saturn... 886.0 9.539 0.0561 2@29'40" 0.012 0.0099 0.011

Uranus.. 1781.9 19.183 0.0463 0@46'20" 0.0027 0.0025 0.003

Neptune. 2791.6 30.055 0.0090 1@47'2" 0.0011 0.0011 0.001

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(1) MOVEMENT IN ORBIT. Velocity compared with earth as 1.

(2) MOVEMENT IN ORBIT. Period of revolution in years and days.

(3) MOVEMENT IN ORBIT. Orbital velocity in miles per second.

(4) Mean diameter in miles

(5) Surface compared with earth as 1.

(6) Volume compared with earth as 1.

(7) Mass compared with earth as 1.

Planets (1) (2) (3) (4) (5) (6) (7)

Mercury..... 0.88 23 to 35 1.6 3,000 0.14 0.056 0.13

Venus.....0.224 1/2 21.9 1.17 7,700 0.94 0.92 0.78

The Earth... 1.00 18.5 1.0 7,918 1.00 1.00 1.00

Mars........ 1.88 15.0 0.81 4,230 0.28 0.139 0.124

Asteroids... 3.29 .... .... From a few to 6.56

miles to 300

Jupiter..... 11.86 8.1 0.44 86,500 118.3 1309.00 316.0

Saturn...... 29.46 6.0 0.32 1,000 0.4 760.0 95.0

Uranus...... 84.02 4.2 0.23 31,900 16.3 65.0 14.7

Neptune.... 164.78 3.4 0.18 34,800 19.3 90.0 17.1

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(1) Length of day. hrs. min. sec.

(2) Length of seasons

(3) DENSITY Compared with earth as 1

(4) DENSITY Compared with water as 1

(5) FORCE OF GRAVITY AT SURFACE OF PLANET Compared with earth as

1.

(6) FORCE OF GRAVITY AT SURFACE OF PLANET Bodies fall in one

second.

(7) Inclination of axis.

Planets (1) (2) (3) (4) (5) (6) (7)

Mercury. ........ ......... 1.24 7.17 0.85 13.7 .....

Venus... 23 21 22 ........ 0.92 5.21 0.83 13.4 53+

The Earth. ..... Spring, 93 1.00 5.67 1.00 16.09 23 1/2

Summer, 93

Terrestrial days Autumn, 90

Winter,89

Mars... 24 37 23 Spring, 191 0.96 2.54 0.38 6.2 27 1/2

Summer, 181

Martian days Autumn, 149

Winter, 147

Asteroids........................................................

Jupiter. 9 55 28 ......... 0.22 1.29 2.55 40.98 1 1/2

Saturn..10 29 17 ......... 0.13 0.63 1.15 18.53 27

Uranus. ....... ......... 0.18 1.41 0.91 14.6 102(?)

Neptune......... ......... 0.20 0 0.88 14.2 .....

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"You see," Ayrault explained, "on Jupiter we shall need our

apergetic outfits to enable us to make long marches, while on

Saturn they will not be necessary, the increase in our weight as

a result of that planet's size being considerably less than the

usual load carried by the Roman soldier."

"I do not imagine," said Cortlandt, "we should long be troubled

by gravitation without our apergetic outfits even on Jupiter,

for, though our weight will be more than doubled, we can take off

one quarter of the whole by remaining near the equator, their

rapid rotation having apparently been given providentially to all

the large planets. Nature will adapt herself to this change, as

to all others, very readily. Although the reclamation of the

vast areas of the North American Arctic Archipelago, Alaska,

Siberia, and Antarctic Wilkes Land, from the death-grip of the

ice in which they have been held will relieve the pressure of

population for another century, at the end of that time it will

surely be felt again; it is therefore a consolation to feel that

the mighty planets Jupiter and Saturn, which we are coming to

look upon as our heritage, will not crush the life out of any

human beings by their own weight that may alight upon them."

Before going to bed that evening they decided to be up early the

next day, to study Jupiter, which was already a brilliant object.

The following morning, on awakening, they went at once to their

observatory, and found that Jupiter's disk was plainly visible to

the naked eye, and before night it seemed as large as the full

moon.

They then prepared to check the Callisto's headlong speed, which

Jupiter's attraction was beginning to increase. When about two