The Scene Shifts
:
SATURN
Having returned the rugs to the Callisto, they applied the
maximum power of the batteries to rising, closed all openings
when the barometer registered thirty, and moved off into space.
When Several thousand miles above the pole, they diverted part of
the power to attracting the nearest moon that was in the plane of
Jupiter's equator, and by the time their upward motion had ceased
were moving well in its direction. Th
ir rapid motion aided the
work of resisting gravity, since their car had in fact become a
small moon, revolving, like those of Uranus or that of Neptune,
in an orbit varying greatly from the plane of the ecliptic. As
they flew south at a height ranging from two thousand to three
thousand miles, the planet revolved before them, and they had a
chance of obtaining a thorough view. There were but a few
scattered islands on the side of the Northern hemisphere opposite
to that over which they had reached the pole, and in the varying
colours of the water, which they attributed to temperature or to
some substance in solution, they recognized what they had always
heard described on earth as the bands of Jupiter, encircling the
planet with great belts, the colour varying with the latitude.
At about latitude forty-five these bands were purple, farther
south light olive green, and at the equator a brown orange.
Shortly after they swung across the equator the ocean again
became purple, and at the same time a well-defined and very
brilliant white spot came into view. Its brightness showed
slight variations in intensity, though its general shape remained
unchanged. It had another peculiarity, in that it possessed a
fairly rapid motion of its own, as it moved eastward across the
surface of the ocean. It exhibited all the phenomena of the
storm they had watched in crossing Secretary Deepwaters Bay, but
covered a larger area, and was far more violent. Their glasses
showed them vast sheets of spray driven along at tremendous
speed, while the surface was milky white.
"This," said Bearwarden, picking up a book, "solves to my mind
the mystery of the white spot described by the English writer
Chambers, in 1889, as follows:
"'During the last few years a brilliant white spot has been
visible on the equatorial border of the great southern belt. A
curious fact in connection with this spot is, that it moves with
a velocity of some two hundred and sixty miles per hour greater
than the red spot. Denning obtained one hundred and sixty-nine
observations of this bright marking during the years 1880-1883,
and determined the period as nine hours, fifty minutes, eight and
seven tenths seconds (five and a half minutes less than that of
the red spot). Although the latter is now somewhat faint, the
white spot gives promise of remaining visible for many years.
During the year 1886 a large number of observations of Jupiter
were made at the Dearborn Observatory, Chicago, U. S., by Prof.
G. W. Hough, using the eighteen-and-a-half-inch refractor of the
observatory. Inasmuch as these observations are not only of high
intrinsic interest, but are in conflict, to some extent, with
previous records, a somewhat full abstract of them will be
useful: The object of general interest was the great red spot.
The outline, shape, and size of this remarkable object has
remained without material change from the year 1879, when it was
first observed here, until the present time. According to our
observations, during the whole of this period it has shown a
sharp and well-defined outline, and at no time has it coalesced
or been joined to any belt in its proximity, as has been alleged
by some observers. During the year 1885 the middle of the spot
was very much paler in colour than the margins, causing it to
appear as an elliptical ring. The ring form has continued up to
the present time. While the outline of the spot has remained
very constant, the colour has changed materially from year to
year. During the past three years (1884- '86) it has at times
been very faint, so as barely to be visible. The persistence of
this object for so many years leads me to infer that the formerly
accepted theory, that the phenomena seen on the surface of the
planet are atmospheric, is no longer tenable. The statement so
often made in text-books, that in the course of a few days or
months the whole aspect of the planet may be changed, is
obviously erroneous. The oval white spots on the southern
hemisphere of the planet, nine degrees south of the equator, have
been systematically observed at every opposition during the past
eight years. They are generally found in groups of three or
more, but are rather difficult to observe. The rotation period
deduced from them is nearly the same as from the great red spot.
These spots usually have a slow drift in longitude of about five
seconds daily in the direction of the planet's rotation, when
referred to the great red spot; corresponding to a rotation
period of twenty seconds less than the latter.'
"This shows," continued Bearwarden, "that as long ago as towards
the close of the nineteenth century the old idea that we saw
nothing but the clouds in Jupiter's atmosphere was beginning to
change; and also how closely the two English writers and Prof.
Hough were studying the subject, though their views did not
entirely agree. A white spot is merely a storm-centre passing
round and round the planet, the wind running a little ahead of
the surface, which accounts for its rapid rotation compared with
the red spot, which is a fixture. A critic may say we have no
such winds on earth; to which I reply, that winds on a planet of
Jupiter's size, with its rate of rotation--though it is
480,000,000 miles from the sun and the internal heat is so near
the surface--and with land and water arranged as they are, may
and indeed must be very different from those prevailing on earth,
the conditions producing and affecting them being so changed.
Though the storm-centre moves two hundred and sixty miles an
hour, the wind need not blow at that rate."
Later they saw several smaller spots drifting eastward, but
concluded that any seaworthy ship might pass safely through them,
for, though they were hurricanes of great violence, the waves
were small.
"There would be less danger," said Bearwarden, "of shipping seas
here than there is on earth; the principal risk to travellers
would be that of being blown from the deck. On account of the
air's weight in connection with its velocity, this would
necessitate some precaution."
The next object of interest was the great red spot. It proved,
as Cortlandt had predicted, to be a continent, with at that time
no special colour, though they easily recognized it by comparing
its outlines with those of the spot in the map. Its length, as
they already knew, was twenty-seven thousand miles, and its
breadth about eight thousand miles, so that it contained more
square miles than the entire surface of the earth, land and water
included.
"It is clear," said Cortlandt, "that at some season of Jupiter's
long year a change takes place that affects the colour of the
leaves--some drought or prolonged norther; for it is obvious that
that is the simplest explanation. In like manner we may expect
that at some times more white spots will move across the ocean
than at others."
"On account of the size of these continents and oceans," said
Bearwarden, "it is easy to believe that many climatic conditions
may prevail here that can scarcely exist on earth. But what a
magnificent world to develop, with its great rivers, lakes, and
mountains showing at even this distance, and what natural
resources must be lying there dormant, awaiting our call! This
constantly recurs to my mind. The subjugation and thorough
opening up of this red spot continent will probably supply more
interesting problems than straightening the axis of the earth."
"At our next visit," replied Ayrault, "when we have established
regular interplanetary lines of travel, we may have an
opportunity to examine it more closely." Then they again
attracted the nearest moon beyond which they had swung, increased
the repulsion on Jupiter, and soared away towards Saturn.
"We have a striking illustration of Jupiter's enormous mass,"
said Cortlandt, as the apparent diameter of the mighty planet
rapidly decreased, "in the fact that notwithstanding its numerous
moons, it still rotates so rapidly. We know that the earth's
days were formerly but half or a quarter as long as now, having
lasted but six or eight hours. The explanation of the elongation
is simple: the earth rotates in about twenty-four hours, while
the moon encircles it but once in nearly twenty- eight days, so
that our satellite is continually drawing the oceans backward
against its motion. These tidal brakes acting through the
friction of the water on the bottom, its unequal pressure, and
the impact of the waves on the shore, are continually retarding
its rotation, so that the day is a fraction of a second longer
now than it was in the time of Caesar. This same action is of
course taking place in Jupiter and the great planets, in this
case there being five moons at work. Our moon, we know, rotates
on its axis but once while it revolves about the earth, this
being no doubt due to its own comparative smallness and the great
attraction of the earth, which must have produced tremendous
tides before the lunar oceans disappeared from its surface."
In crossing the orbits of the satellites, they passed near
Ganymede, Jupiter's largest moon.
"This," said Cortlandt, "was discovered by Galileo in
1610. It is three thousand four hundred and eighty miles
in diameter, while our moon is but two thousand one
hundred and sixty, revolves at a distance of six hundred
and seventy-eight thousand three hundred miles from
Jupiter, completes its revolution in seven days and four
hours, and has a specific gravity of 1.87."
In passing, they observed that Ganymede possessed an atmosphere,
and continents and oceans of large area.
"Here," said Bearwarden, "we have a body with a diameter about
five hundred miles greater than the planet Mercury. Its size,
light specific gravity, atmosphere, and oceans seem to indicate
that it is less advanced than that planet, yet you think Jupiter
has had a longer separate existence than the planets nearer the
sun?"
"Undoubtedly," said Cortlandt. "Jupiter was condensed while in
the solar-system nebula, and began its individual existence and
its evolutionary career long before Mercury was formed. The
matter now in Ganymede, however, doubtless remained part of the
Jupiter-system nebula till after Mercury's creation, and, being
part of so great a mass, did not cool very rapidly. I should say
that this satellite has about the same relation to Jupiter that
Jupiter has to the sun, and is therefore younger in point of time
as well as of development than the most distant Callisto, and
older, at all events in years, than Europa and Io, both of which
are nearer. This supposition is corroborated by the fact that
Europa, the smallest of these four, is also the densest, having a
specific gravity of 2.14, its smallness having enabled it to
overtake Ganymede in development, notwithstanding the latter's
start. In the face of the evidence before us we must believe
this, or else that, perhaps, as in the case of the asteroid
Hilda, something like a collision has rejuvenated it. This might
account for its size, and for the Nautical Almanac's statement
that there is a 'small and variable' inclination to its orbit,
while Io and Europa revolve exactly in the plane of Jupiter's
equator."
They had about as long a journey before them as they had already
made in going from the earth to Jupiter. The great planet soon
appeared as a huge crescent, since it was between them and the
sun; its moons became as fifth- and sixth-magnitude stars, and in
the evening of the next day Jupiter's disk became invisible to
the unaided eye. Since there were no way stations, in the shape
of planets or asteroids, between Jupiter and Saturn, they kept
the maximum repulsion on Jupiter as long as possible, and moved
at tremendous speed. Saturn was somewhat in advance of Jupiter
in its orbit, so that their course from the earth had been along
two sides of a triangle with an obtuse angle between. During the
next four terrestrial days they sighted several small comets, but
spent most of their time writing out their Jovian experiences.
During the sixth day Saturn's rings, although not as much tilted
as they would be later in the planet's season, presented a most
superb sight, while they spun in the sun's rays. Soon after this
the eight moons became visible, and, while slightly reducing the
Callisto's speed, they crossed the orbits of Iapetus, Hyperion,
and Titan, when they knew they were but seven hundred and fifty
thousand miles from Saturn.
"I am anxious to ascertain," said Cortlandt, "whether the
composition of yonder rings is similar to that of the comet
through which we passed. I am sure they shine with more than
reflected light."
"We have been in the habit," said Ayrault, "of associating heat
with light, but it is obvious there is something far more subtle
about cometary light and that of Saturn's rings, both of which
seem to have their birth in the intense cold of interplanetary
space."
Passing close to Mimas, Saturn's nearest moon, they supplemented
its attraction, after swinging by, by their own strong pull,
bringing their speed down to dead slow as they entered the
outside ring. At distances often of half a mile they found
meteoric masses, sometimes lumps the size of a house, often no
larger than apples, while small particles like grains of sand
moved between them. There were two motions. The ring revolved
about Saturn, and the particles vibrated among themselves,
evidently kept apart by a mutual repulsion, which seemed both to
increase and decrease faster than gravitation; for on approaching
one another they were more strongly repelled than attracted, but
when they separated the repulsion decreased faster than the
attraction, so that after a time divergence ceased, and they
remained at fixed distances.
The Callisto soon became imbued with motion also, but nothing
ever struck it. When any large mass came unusually near, both it
and their car emitted light, and they rapidly separated. The
sunlight was not as strong here as it had been when they entered
the comet, and as they penetrated farther they were better able
to observe the omnipresent luminosity. They were somewhat
puzzled by the approach of certain light-centres, which seemed to
contain nothing but this concentrated brightness. Occasionally
one of these centres would glow very brightly near them, and
simultaneously recede. At such times the Callisto also glowed,
and itself recoiled slightly. At first the travellers could not
account for this, but finally they concluded that the centres
must be meteoric masses consisting entirely of gases, possessing
weight though invisible.
"We have again to face," said Cortlandt, "that singular law that
till recently we did not suppose existed on earth. All kinds of
suppositions have been advanced in explanation of these rings.
Some writers have their thickness, looked at from the thin edge,
as four hundred miles, some one hundred, and some but forty. One
astronomer of the nineteenth century, a man of considerable
eminence, was convinced that they consisted of sheets of liquid.
Now, it should be obvious that no liquid could maintain itself
here for a minute, for it would either fall upon the planet as a
crushing hail, or, if dependent for its shape on its own
tenacity, it would break if formed of the toughest steel, on
account of the tremendous weight. Any number of theories have
been advanced by any number of men, but in weight we have the
rub. No one has ever shown how these innumerable fragments
maintain themselves at a height of but a few thousand miles above
Saturn, withstanding the giant's gravitation-pull. Their rate of
revolution, though rapid, does not seem fast enough to sustain
them. Neither have I ever seen it explained why the small
fragments do not fall upon the large ones, though many
astronomers have pictured the composition of these rings as we
find they exist. Nor do we know why the molecules of a gas are
driven farther apart by heat, while their activity is also
increased, though if this activity were revolution about one
another to develop the centrifugal, it would not need to be as
strong then as when they are cold and nearer together. There may
be explanations, but I have found none in any of the literature I
have read. It seems to me that all this leads to but one
conclusion, viz.: apergy is the constant and visible companion of
gravitation, on these great planets Jupiter and Saturn, perhaps
on account of some peculiar influence they possess, and also in
comets, in the case of large masses, while on earth it appears
naturally only among molecules--those of gases and every other
substance."
"I should go a step further," said Bearwarden, "and say our earth
has the peculiarity, since it does not possess the influence
necessary to generate naturally a great or even considerable
development of apergy. The electricity of thunderstorms,
northern lights, and other forces seems to be produced freely,
but as regards apergy our planet's natural productiveness appears
to be small."
The omnipresent luminosity continued, but the glow was scarcely
bright enough to be perceived from the earth.
"I believe, however," said Bearwarden, referring to this, "that
whenever a satellite passes near these fragments, preferably when
it enters the planet's shadow, since that will remove its own
light, it will create such activity among them as to make the
luminosity visible to the large telescopes or gelatine plates on
earth."
"Now," said Ayrault, "that we have evolved enough theories to
keep astronomers busy for some time, if they attempt to discuss
them, I suggest that we alight and leave the abstract for the
concrete."
Whereupon they passed through the inner ring and rapidly sank to
the ground.