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SIDE-LIGHTS ON ASTRONOMY
AND KINDRED FIELDS OF POPULAR SCIENCE
ESSAYS AND ADDRESSES
BY
SIMON NEWCOMB
CONTENTS
PREFACE
I. THE UNSOLVED PROBLEMS OF ASTRONOMY
II. THE NEW PROBLEMS OF THE UNIVERSE
III. THE STRUCTURE OF THE UNIVERSE
IV. THE EXTENT OF THE UNIVERSE
V. MAKING AND USING A TELESCOPE
VI. WHAT THE ASTRONOMERS ARE DOING
VII. LIFE IN THE UNIVERSE
VIII. HOW THE PLANETS ARE WEIGHED
IX. THE MARINER'S COMPASS
X. THE FAIRYLAND OF GEOMETRY
XI. THE ORGANIZATION OF SCIENTIFIC RESEARCH
XII. CAN WE MAKE IT RAIN?
XIII. THE ASTRONOMICAL EPHEMERIS AND NAUTICAL ALMANAC
XIV. THE WORLD'S DEBT TO ASTRONOMY
XV. AN ASTRONOMICAL FRIENDSHIP
XVI. THE EVOLUTION OF THE SCIENTIFIC INVESTIGATOR
XVII. THE EVOLUTION OF ASTRONOMICAL KNOWLEDGE
XVIII. ASPECTS OF AMERICAN ASTRONOMY
XIX. THE UNIVERSE AS AN ORGANISM
XX. THE RELATION OF SCIENTIFIC METHOD TO SOCIAL PROGRESS
XXI. THE OUTLOOK FOR THE FLYING-MACHINE
ILLUSTRATIONS
SIMON NEWCOMB
PHOTOGRAPH OF THE CORONA OF THE SUN, TAKEN IN TRIPOLI DURING TOTAL
ECLIPSE OF AUGUST 30, 1905.
A TYPICAL STAR CLUSTER-CENTAURI
THE GLASS DISK
THE OPTICIAN'S TOOL
THE OPTICIAN'S TOOL
GRINDING A LARGE LENS
IMAGE OF CANDLE-FLAME IN OBJECT-GLASS
TESTING ADJUSTMENT OF OBJECT-GLASS
A VERY PRIMITIVE MOUNTING FOR A TELESCOPE
THE HUYGHENIAN EYE-PIECE
SECTION OF THE PRIMITIVE MOUNTING
SPECTRAL IMAGES OF STARS, THE UPPER LINE SHOWING HOW THEY APPEAR WITH
THE EYE-PIECE PUSHED IN, THE LOWER WITH THE EYE-PIECE DRAWN OUT
THE GREAT REFRACTOR OF THE NATIONAL OBSERVATORY AT WASHINGTON
THE "BROKEN-BACKED COMET-SEEKER"
NEBULA IN ORION
DIP OF THE MAGNETIC NEEDLE IN VARIOUS LATITUDES
STAR SPECTRA
PROFESSOR LANGLEY'S AIR-SHIP
PREFACE
In preparing and issuing this collection of essays and addresses, the
author has yielded to what he could not but regard as the too
flattering judgment of the publishers. Having done this, it became
incumbent to do what he could to justify their good opinion by revising
the material and bringing it up to date. Interest rather than unity of
thought has determined the selection.
A prominent theme in the collection is that of the structure, extent,
and duration of the universe. Here some repetition of ideas was found
unavoidable, in a case where what is substantially a single theme has
been treated in the various forms which it assumed in the light of
constantly growing knowledge. If the critical reader finds this a
defect, the author can plead in extenuation only the difficulty of
avoiding it under the circumstances. Although mainly astronomical, a
number of discussions relating to general scientific subjects have been
included.
Acknowledgment is due to the proprietors of the various periodicals
from the pages of which most of the essays have been taken. Besides
Harper's Magazine and the North American Review, these include
McClure's Magazine, from which were taken the articles "The Unsolved
Problems of Astronomy" and "How the Planets are Weighed." "The
Structure of the Universe" appeared in the International Monthly, now
the International Quarterly; "The Outlook for the Flying-Machine" is
mainly from The New York Independent, but in part from McClure's
Magazine; "The World's Debt to Astronomy" is from The Chautauquan; and
"An Astronomical Friendship" from the Atlantic Monthly.
SIMON NEWCOMB. WASHINGTON, JUNE, 1906.
I
THE UNSOLVED PROBLEMS OF ASTRONOMY
The reader already knows what the solar system is: an immense central
body, the sun, with a number of planets revolving round it at various
distances. On one of these planets we dwell. Vast, indeed, are the
distances of the planets when measured by our terrestrial standards. A
cannon-ball fired from the earth to celebrate the signing of the
Declaration of Independence, and continuing its course ever since with
a velocity of eighteen hundred feet per second, would not yet be
half-way to the orbit of Neptune, the outer planet. And yet the
thousands of stars which stud the heavens are at distances so much
greater than that of Neptune that our solar system is like a little
colony, separated from the rest of the universe by an ocean of void
space almost immeasurable in extent. The orbit of the earth round the
sun is of such size that a railway train running sixty miles an hour,
with never a stop, would take about three hundred and fifty years to
cross it. Represent this orbit by a lady's finger-ring. Then the
nearest fixed star will be about a mile and a half away; the next more
than two miles; a few more from three to twenty miles; the great body
at scores or hundreds of miles. Imagine the stars thus scattered from
the Atlantic to the Mississippi, and keep this little finger-ring in
mind as the orbit of the earth, and one may have some idea of the
extent of the universe.
One of the most beautiful stars in the heavens, and one that can be
seen most of the year, is a Lyrae, or Alpha of the Lyre, known also as
Vega. In a spring evening it may be seen in the northeast, in the later
summer near the zenith, in the autumn in the northwest. On the scale we
have laid down with the earth's orbit as a finger-ring, its distance
would be some eight or ten miles. The small stars around it in the same
constellation are probably ten, twenty, or fifty times as far.
Now, the greatest fact which modern science has brought to light is
that our whole solar system, including the sun, with all its planets,
is on a journey towards the constellation Lyra. During our whole lives,
in all probability during the whole of human history, we have been
flying unceasingly towards this beautiful constellation with a speed to
which no motion on earth can compare. The speed has recently been
determined with a fair degree of certainty, though not with entire
exactness; it is about ten miles a second, and therefore not far from
three hundred millions of miles a year. But whatever it may be, it is
unceasing and unchanging; for us mortals eternal. We are nearer the
constellation by five or six hundred miles every minute we live; we are
nearer to it now than we were ten years ago by thousands of millions of
miles, and every future generation of our race will be nearer than its
predecessor by thousands of millions of miles.
When, where, and how, if ever, did this journey begin--when, where, and
how, if ever, will it end? This is the greatest of the unsolved
problems of astronomy. An astronomer who should watch the heavens for
ten thousand years might gather some faint suggestion of an answer, or
he might not. All we can do is to seek for some hints by study and
comparison with other stars.
The stars are suns. To put it in another way, the sun is one of the
stars, and rather a small one at that. If the sun is moving in the way
I have described, may not the stars also be in motion, each on a
journey of its own through the wilderness of space? To this question
astronomy gives an affirmative answer. Most of the stars nearest to us
are found to be in motion, some faster than the sun, some more slowly,
and the same is doubtless true of all; only the century of accurate
observations at our disposal does not show the motion of the distant
ones. A given motion seems slower the more distant the moving body; we
have to watch a steamship on the horizon some little time to see that
she moves at all. Thus it is that the unsolved problem of the motion of
our sun is only one branch of a yet more stupendous one: What mean the
motions of the stars--how did they begin, and how, if ever, will they
end? So far as we can yet see, each star is going straight ahead on its
own journey, without regard to its neighbors, if other stars can be so
called. Is each describing some vast orbit which, though looking like a
straight line during the short period of our observation, will really
be seen to curve after ten thousand or a hundred thousand years, or
will it go straight on forever? If the laws of motion are true for all
space and all time, as we are forced to believe, then each moving star
will go on in an unbending line forever unless hindered by the
attraction of other stars. If they go on thus, they must, after
countless years, scatter in all directions, so that the inhabitants of
each shall see only a black, starless sky.
Mathematical science can throw only a few glimmers of light on the
questions thus suggested. From what little we know of the masses,
distances, and numbers of the stars we see a possibility that the more
slow-moving ones may, in long ages, be stopped in their onward courses
or brought into orbits of some sort by the attraction of their millions
of fellows. But it is hard to admit even this possibility in the case
of the swift-moving ones. Attraction, varying as the inverse square of
the distance, diminishes so rapidly as the distance increases that, at
the distances which separate the stars, it is small indeed. We could
not, with the most delicate balance that science has yet invented, even
show the attraction of the greatest known star. So far as we know, the
two swiftest-moving stars are, first, Arcturus, and, second, one known
in astronomy as 1830 Groombridge, the latter so called because it was
first observed by the astronomer Groombridge, and is numbered 1830 in
his catalogue of stars. If our determinations of the distances of these
bodies are to be relied on, the velocity of their motion cannot be much
less than two hundred miles a second. They would make the circuit of
the earth every two or three minutes. A body massive enough to control
this motion would throw a large part of the universe into disorder.
Thus the problem where these stars came from and where they are going
is for us insoluble, and is all the more so from the fact that the
swiftly moving stars are moving in different directions and seem to
have no connection with each other or with any known star.
It must not be supposed that these enormous velocities seem so to us.
Not one of them, even the greatest, would be visible to the naked eye
until after years of watching. On our finger-ring scale, 1830
Groombridge would be some ten miles and Arcturus thirty or forty miles
away. Either of them would be moving only two or three feet in a year.
To the oldest Assyrian priests Lyra looked much as it does to us
to-day. Among the bright and well-known stars Arcturus has the most
rapid apparent motion, yet Job himself would not to-day see that its
position had changed, unless he had noted it with more exactness than
any astronomer of his time.
Another unsolved problem among the greatest which present themselves to
the astronomer is that of the size of the universe of stars. We know
that several thousand of these bodies are visible to the naked eye;
moderate telescopes show us millions; our giant telescopes of the
present time, when used as cameras to photograph the heavens, show a
number past count, perhaps one hundred millions. Are all these stars
only those few which happen to be near us in a universe extending out
without end, or do they form a collection of stars outside of which is
empty infinite space? In other words, has the universe a boundary?
Taken in its widest scope this question must always remain unanswered
by us mortals because, even if we should discover a boundary within
which all the stars and clusters we ever can know are contained, and
outside of which is empty space, still we could never prove that this
space is empty out to an infinite distance. Far outside of what we call
the universe might still exist other universes which we can never see.
It is a great encouragement to the astronomer that, although he cannot
yet set any exact boundary to this universe of ours, he is gathering
faint indications that it has a boundary, which his successors not many
generations hence may locate so that the astronomer shall include
creation itself within his mental grasp. It can be shown mathematically
that an infinitely extended system of stars would fill the heavens with
a blaze of light like that of the noonday sun. As no such effect is
produced, it may be concluded that the universe has a boundary. But
this does not enable us to locate the boundary, nor to say how many
stars may lie outside the farthest stretches of telescopic vision. Yet
by patient research we are slowly throwing light on these points and
reaching inferences which, not many years ago, would have seemed
forever beyond our powers.
Every one now knows that the Milky Way, that girdle of light which
spans the evening sky, is formed of clouds of stars too minute to be
seen by the unaided vision. It seems to form the base on which the
universe is built and to bind all the stars into a system. It comprises
by far the larger number of stars that the telescope has shown to
exist. Those we see with the naked eye are almost equally scattered
over the sky. But the number which the telescope shows us become more
and more condensed in the Milky Way as telescope power is increased.
The number of new stars brought out with our greatest power is vastly
greater in the Milky Way than in the rest of the sky, so that the
former contains a great majority of the stars. What is yet more
curious, spectroscopic research has shown that a particular kind of
stars, those formed of heated gas, are yet more condensed in the
central circle of this band; if they were visible to the naked eye, we
should see them encircling the heavens as a narrow girdle forming
perhaps the base of our whole system of stars. This arrangement of the
gaseous or vaporous stars is one of the most singular facts that modern
research has brought to light. It seems to show that these particular
stars form a system of their own; but how such a thing can be we are
still unable to see.
The question of the form and extent of the Milky Way thus becomes the
central one of stellar astronomy. Sir William Herschel began by trying
to sound its depths; at one time he thought he had succeeded; but
before he died he saw that they were unfathomable with his most
powerful telescopes. Even today he would be a bold astronomer who would
profess to say with certainty whether the smallest stars we can
photograph are at the boundary of the system. Before we decide this
point we must have some idea of the form and distance of the cloudlike
masses of stars which form our great celestial girdle. A most curious
fact is that our solar system seems to be in the centre of this
galactic universe, because the Milky Way divides the heavens into two
equal parts, and seems equally broad at all points. Were we looking at
such a girdle as this from one side or the other, this appearance would
not be presented. But let us not be too bold. Perhaps we are the
victims of some fallacy, as Ptolemy was when he proved, by what looked
like sound reasoning, based on undeniable facts, that this earth of
ours stood at rest in the centre of the heavens!
A related problem, and one which may be of supreme importance to the
future of our race, is, What is the source of the heat radiated by the
sun and stars? We know that life on the earth is dependent on the heat
which the sun sends it. If we were deprived of this heat we should in a
few days be enveloped in a frost which would destroy nearly all
vegetation, and in a few months neither man nor animal would be alive,
unless crouching over fires soon to expire for want of fuel. We also
know that, at a time which is geologically recent, the whole of New
England was covered with a sheet of ice, hundreds or even thousands of
feet thick, above which no mountain but Washington raised its head. It
is quite possible that a small diminution in the supply of heat sent us
by the sun would gradually reproduce the great glacier, and once more
make the Eastern States like the pole. But the fact is that
observations of temperature in various countries for the last two or
three hundred years do not show any change in climate which can be
attributed to a variation in the amount of heat received from the sun.
The acceptance of this theory of the heat of those heavenly bodies
which shine by their own light--sun, stars, and nebulae--still leaves
open a problem that looks insoluble with our present knowledge. What
becomes of the great flood of heat and light which the sun and stars
radiate into empty space with a velocity of one hundred and eighty
thousand miles a second? Only a very small fraction of it can be
received by the planets or by other stars, because these are mere
points compared with their distance from us. Taking the teaching of our
science just as it stands, we should say that all this heat continues
to move on through infinite space forever. In a few thousand years it
reaches the probable confines of our great universe. But we know of no
reason why it should stop here. During the hundreds of millions of
years since all our stars began to shine, has the first ray of light
and heat kept on through space at the rate of one hundred and eighty
thousand miles a second, and will it continue to go on for ages to
come? If so, think of its distance now, and think of its still going
on, to be forever wasted! Rather say that the problem, What becomes of
it? is as yet unsolved.
Thus far I have described the greatest of problems; those which we may
suppose to concern the inhabitants of millions of worlds revolving
round the stars as much as they concern us. Let us now come down from
the starry heights to this little colony where we live, the solar
system. Here we have the great advantage of being better able to see
what is going on, owing to the comparative nearness of the planets.
When we learn that these bodies are like our earth in form, size, and
motions, the first question we ask is, Could we fly from planet to
planet and light on the surface of each, what sort of scenery would
meet our eyes? Mountain, forest, and field, a dreary waste, or a
seething caldron larger than our earth? If solid land there is, would
we find on it the homes of intelligent beings, the lairs of wild
beasts, or no living thing at all? Could we breathe the air, would we
choke for breath or be poisoned by the fumes of some noxious gas?
To most of these questions science cannot as yet give a positive
answer, except in the case of the moon. Our satellite is so near us
that we can see it has no atmosphere and no water, and therefore cannot
be the abode of life like ours. The contrast of its eternal deadness
with the active life around us is great indeed. Here we have weather of
so many kinds that we never tire of talking about it. But on the moon
there is no weather at all. On our globe so many things are constantly
happening that our thousands of daily journals cannot begin to record
them. But on the dreary, rocky wastes of the moon nothing ever happens.
So far as we can determine, every stone that lies loose on its surface
has lain there through untold ages, unchanged and unmoved.
We cannot speak so confidently of the planets. The most powerful
telescopes yet made, the most powerful we can ever hope to make, would
scarcely shows us mountains, or lakes, rivers, or fields at a distance
of fifty millions of miles. Much less would they show us any works of
man. Pointed at the two nearest planets, Venus and Mars, they whet our
curiosity more than they gratify it. Especially is this the case with
Venus. Ever since the telescope was invented observers have tried to
find the time of rotation of this planet on its axis. Some have reached
one conclusion, some another, while the wisest have only doubted. The
great Herschel claimed that the planet was so enveloped in vapor or
clouds that no permanent features could be seen on its surface. The
best equipped recent observers think they see faint, shadowy patches,
which remain the same from day to day, and which show that the planet
always presents the same face to the sun, as the moon does to the
earth. Others do not accept this conclusion as proved, believing that
these patches may be nothing more than variations of light, shade, and
color caused by the reflection of the sun's light at various angles
from different parts of the planet.
There is also some mystery about the atmosphere of this planet. When
Venus passes nearly between us and the sun, her dark hemisphere is
turned towards us, her bright one being always towards the sun. But she
is not exactly on a line with the sun except on the very rare occasions
of a transit across the sun's disk. Hence, on ordinary occasions, when
she seems very near on a line with the sun, we see a very small part of
the illuminated hemisphere, which now presents the form of a very thin
crescent like the new moon. And this crescent is supposed to be a
little broader than it would be if only half the planet were
illuminated, and to encircle rather more than half the planet. Now,
this is just the effect that would be produced by an atmosphere
refracting the sun's light around the edge of the illuminated
hemisphere.
The difficulty of observations of this kind is such that the conclusion
may be open to doubt. What is seen during transits of Venus over the
sun's disk leads to more certain, but yet very puzzling, conclusions.
The writer will describe what he saw at the Cape of Good Hope during
the transit of December 5, 1882. As the dark planet impinged on the
bright sun, it of course cut out a round notch from the edge of the
sun. At first, when this notch was small, nothing could be seen of the
outline of that part of the planet which was outside the sun. But when
half the planet was on the sun, the outline of the part still off the
sun was marked by a slender arc of light. A curious fact was that this
arc did not at first span the whole outline of the planet, but only
showed at one or two points. In a few moments another part of the
outline appeared, and then another, until, at last, the arc of light
extended around the complete outline. All this seems to show that while
the planet has an atmosphere, it is not transparent like ours, but is
so filled with mist and clouds that the sun is seen through it only as
if shining in a fog.
Not many years ago the planet Mars, which is the next one outside of
us, was supposed to have a surface like that of our earth. Some parts
were of a dark greenish gray hue; these were supposed to be seas and
oceans. Other parts had a bright, warm tint; these were supposed to be
the continents. During the last twenty years much has been learned as
to how this planet looks, and the details of its surface have been
mapped by several observers, using the best telescopes under the most
favorable conditions of air and climate. And yet it must be confessed
that the result of this labor is not altogether satisfactory. It seems
certain that the so-called seas are really land and not water. When it
comes to comparing Mars with the earth, we cannot be certain of more
than a single point of resemblance. This is that during the Martian
winter a white cap, as of snow, is formed over the pole, which
partially melts away during the summer. The conclusion that there are
oceans whose evaporation forms clouds which give rise to this snow
seems plausible. But the telescope shows no clouds, and nothing to make
it certain that there is an atmosphere to sustain them. There is no
certainty that the white deposit is what we call snow; perhaps it is
not formed of water at all. The most careful studies of the surface of
this planet, under the best conditions, are those made at the Lowell
Observatory at Flagstaff, Arizona. Especially wonderful is the system
of so-called canals, first seen by Schiaparelli, but mapped in great
detail at Flagstaff. But the nature and meaning of these mysterious
lines are still to be discovered. The result is that the question of
the real nature of the surface of Mars and of what we should see around
us could we land upon it and travel over it are still among the
unsolved problems of astronomy.
If this is the case with the nearest planets that we can study, how is
it with more distant ones? Jupiter is the only one of these of the
condition of whose surface we can claim to have definite knowledge. But
even this knowledge is meagre. The substance of what we know is that
its surface is surrounded by layers of what look like dense clouds,
through which nothing can certainly be seen.
I have already spoken of the heat of the sun and its probable origin.
But the question of its heat, though the most important, is not the
only one that the sun offers us. What is the sun? When we say that it
is a very hot globe, more than a million times as large as the earth,
and hotter than any furnace that man can make, so that literally "the
elements melt with fervent heat" even at its surface, while inside they
are all vaporized, we have told the most that we know as to what the
sun really is. Of course we know a great deal about the spots, the
rotation of the sun on its axis, the materials of which it is composed,
and how its surroundings look during a total eclipse. But all this does
not answer our question. There are several mysteries which ingenious
men have tried to explain, but they cannot prove their explanations to
be correct. One is the cause and nature of the spots. Another is that
the shining surface of the sun, the "photosphere," as it is technically
called, seems so calm and quiet while forces are acting within it of a
magnitude quite beyond our conception. Flames in which our earth and
everything on it would be engulfed like a boy's marble in a
blacksmith's forge are continually shooting up to a height of tens of
thousands of miles. One would suppose that internal forces capable of
doing this would break the surface up into billows of fire a thousand
miles high; but we see nothing of the kind. The surface of the sun
seems almost as placid as a lake.
Yet another mystery is the corona of the sun. This is something we
should never have known to exist if the sun were not sometimes totally
eclipsed by the dark body of the moon. On these rare occasions the sun
is seen to be surrounded by a halo of soft, white light, sending out
rays in various directions to great distances. This halo is called the
corona, and has been most industriously studied and photographed during
nearly every total eclipse for thirty years. Thus we have learned much
about how it looks and what its shape is. It has a fibrous, woolly
structure, a little like the loose end of a much-worn hempen rope. A
certain resemblance has been seen between the form of these seeming
fibres and that of the lines in which iron filings arrange themselves
when sprinkled on paper over a magnet. It has hence been inferred that
the sun has magnetic properties, a conclusion which, in a general way,
is supported by many other facts. Yet the corona itself remains no less
an unexplained phenomenon.
[Illustration with caption: PHOTOGRAPH OF THE CORONA OF THE SUN, TAKEN
IN TRIPOLI DURING TOTAL ECLIPSE OF AUGUST 30, 1905]
A phenomenon almost as mysterious as the solar corona is the "zodiacal
light," which any one can see rising from the western horizon just
after the end of twilight on a clear winter or spring evening. The most
plausible explanation is that it is due to a cloud of small meteoric
bodies revolving round the sun. We should hardly doubt this explanation
were it not that this light has a yet more mysterious appendage,
commonly called the Gegenschein, or counter-glow. This is a patch of
light in the sky in a direction exactly opposite that of the sun. It is
so faint that it can be seen only by a practised eye under the most
favorable conditions. But it is always there. The latest suggestion is
that it is a tail of the earth, of the same kind as the tail of a comet!
We know that the motions of the heavenly bodies are predicted with
extraordinary exactness by the theory of gravitation. When one finds
that the exact path of the moon's shadow on the earth during a total
eclipse of the sun can be mapped out many years in advance, and that
the planets follow the predictions of the astronomer so closely that,
if you could see the predicted planet as a separate object, it would
look, even in a good telescope, as if it exactly fitted over the real
planet, one thinks that here at least is a branch of astronomy which is
simply perfect. And yet the worlds themselves show slight deviations in
their movements which the astronomer cannot always explain, and which
may be due to some hidden cause that, when brought to light, shall lead
to conclusions of the greatest importance to our race.
One of these deviations is in the rotation of the earth. Sometimes, for
several years at a time, it seems to revolve a little faster, and then
again a little slower. The changes are very slight; they can be
detected only by the most laborious and refined methods; yet they must
have a cause, and we should like to know what that cause is.
The moon shows a similar irregularity of motion. For half a century,
perhaps through a whole century, she will go around the earth a little
ahead of her regular rate, and then for another half-century or more
she will fall behind. The changes are very small; they would never have
been seen with the unaided eye, yet they exist. What is their cause?
Mathematicians have vainly spent years of study in trying to answer
this question.
The orbit of Mercury is found by observations to have a slight motion
which mathematicians have vainly tried to explain. For some time it was
supposed to be caused by the attraction of an unknown planet between
Mercury and the sun, and some were so sure of the existence of this
planet that they gave it a name, calling it Vulcan. But of late years
it has become reasonably certain that no planet large enough to produce
the effect observed can be there. So thoroughly has every possible
explanation been sifted out and found wanting, that some astronomers
are now inquiring whether the law of gravitation itself may not be a
little different from what has always been supposed. A very slight
deviation, indeed, would account for the facts, but cautious
astronomers want other proofs before regarding the deviation of
gravitation as an established fact.
Intelligent men have sometimes inquired how, after devoting so much
work to the study of the heavens, anything can remain for astronomers
to find out. It is a curious fact that, although they were never
learning so fast as at the present day, yet there seems to be more to
learn now than there ever was before. Great and numerous as are the
unsolved problems of our science, knowledge is now advancing into
regions which, a few years ago, seemed inaccessible. Where it will stop
none can say.
II
THE NEW PROBLEMS OF THE UNIVERSE
The achievements of the nineteenth century are still a theme of
congratulation on the part of all who compare the present state of the
world with that of one hundred years ago. And yet, if we should fancy
the most sagacious prophet, endowed with a brilliant imagination, to
have set forth in the year 1806 the problems that the century might
solve and the things which it might do, we should be surprised to see
how few of his predictions had come to pass. He might have fancied
aerial navigation and a number of other triumphs of the same class, but
he would hardly have had either steam navigation or the telegraph in
his picture. In 1856 an article appeared in Harper's Magazine depicting
some anticipated features of life in A.D. 3000. We have since made
great advances, but they bear little resemblance to what the writer
imagined. He did not dream of the telephone, but did describe much that
has not yet come to pass and probably never will.
The fact is that, much as the nineteenth century has done, its last
work was to amuse itself by setting forth more problems for this
century to solve than it has ever itself succeeded in mastering. We
should not be far wrong in saying that to-day there are more riddles in
the universe than there were before men knew that it contained anything
more than the objects they could see.
So far as mere material progress is concerned, it may be doubtful
whether anything so epoch-making as the steam-engine or the telegraph
is held in store for us by the future. But in the field of purely
scientific discovery we are finding a crowd of things of which our
philosophy did not dream even ten years ago.
The greatest riddles which the nineteenth century has bequeathed to us
relate to subjects so widely separated as the structure of the universe
and the structure of atoms of matter. We see more and more of these
structures, and we see more and more of unity everywhere, and yet new
facts difficult of explanation are being added more rapidly than old
facts are being explained.
We all know that the nineteenth century was marked by a separation of
the sciences into a vast number of specialties, to the subdivisions of
which one could see no end. But the great work of the twentieth century
will be to combine many of these specialties. The physical philosopher
of the present time is directing his thought to the demonstration of
the unity of creation. Astronomical and physical researches are now
being united in a way which is bringing the infinitely great and the
infinitely small into one field of knowledge. Ten years ago the atoms
of matter, of which it takes millions of millions to make a drop of
water, were the minutest objects with which science could imagine
itself to be concerned, Now a body of experimentalists, prominent among
whom stand Professors J. J. Thompson, Becquerel, and Roentgen, have
demonstrated the existence of objects so minute that they find their
way among and between the atoms of matter as rain-drops do among the
buildings of a city. More wonderful yet, it seems likely, although it
has not been demonstrated, that these little things, called
"corpuscles," play an important part in what is going on among the
stars. Whether this be true or not, it is certain that there do exist
in the universe emanations of some sort, producing visible effects, the
investigation of which the nineteenth century has had to bequeath to
the twentieth.
For the purpose of the navigator, the direction of the magnetic needle
is invariable in any one place, for months and even years; but when
exact scientific observations on it are made, it is found subject to
numerous slight changes. The most regular of these consists in a daily
change of its direction. It moves one way from morning until noon, and
then, late in the afternoon and during the night, turns back again to
its original pointing. The laws of this change have been carefully
studied from observations, which show that it is least at the equator
and larger as we go north into middle latitudes; but no explanation of
it resting on an indisputable basis has ever been offered.
Besides these regular changes, there are others of a very irregular
character. Every now and then the changes in the direction of the
magnet are wider and more rapid than those which occur regularly every
day. The needle may move back and forth in a way so fitful as to show
the action of some unusual exciting cause. Such movements of the needle
are commonly seen when there is a brilliant aurora. This connection
shows that a magnetic storm and an aurora must be due to the same or
some connected causes.
Those of us who are acquainted with astronomical matters know that the
number of spots on the sun goes through a regular cycle of change,
having a period of eleven years and one or two months. Now, the curious
fact is, when the number and violence of magnetic storms are recorded
and compared, it is found that they correspond to the spots on the sun,
and go through the same period of eleven years. The conclusion seems
almost inevitable: magnetic storms are due to some emanation sent out
by the sun, which arises from the same cause that produces the spots.
This emanation does not go on incessantly, but only in an occasional
way, as storms follow each other on the earth. What is it? Every
attempt to detect it has been in vain. Professor Hale, at the Yerkes
Observatory, has had in operation from time to time, for several years,
his ingenious spectroheliograph, which photographs the sun by a single
ray of the spectrum. This instrument shows that violent actions are
going on in the sun, which ordinary observation would never lead us to
suspect. But it has failed to show with certainty any peculiar
emanation at the time of a magnetic storm or anything connected with
such a storm.
A mystery which seems yet more impenetrable is associated with the
so-called new stars which blaze forth from time to time. These offer to
our sight the most astounding phenomena ever presented to the physical
philosopher. One hundred years ago such objects offered no mystery.
There was no reason to suppose that the Creator of the universe had
ceased His functions; and, continuing them, it was perfectly natural
that He should be making continual additions to the universe of stars.
But the idea that these objects are really new creations, made out of
nothing, is contrary to all our modern ideas and not in accord with the
observed facts. Granting the possibility of a really new star--if such
an object were created, it would be destined to take its place among
the other stars as a permanent member of the universe. Instead of this,
such objects invariably fade away after a few months, and are changed
into something very like an ordinary nebula. A question of transcendent
interest is that of the cause of these outbursts. It cannot be said
that science has, up to the present time, been able to offer any
suggestion not open to question. The most definite one is the collision
theory, according to which the outburst is due to the clashing together
of two stars, one or both of which might previously have been dark,
like a planet. The stars which may be actually photographed probably
exceed one hundred millions in number, and those which give too little
light to affect the photographic plate may be vastly more numerous than
those which do. Dark stars revolve around bright ones in an infinite
variety of ways, and complex systems of bodies, the members of which
powerfully attract each other, are the rule throughout the universe.
Moreover, we can set no limit to the possible number of dark or
invisible stars that may be flying through the celestial spaces. While,
therefore, we cannot regard the theory of collision as established, it
seems to be the only one yet put forth which can lay any claim to a
scientific basis. What gives most color to it is the extreme suddenness
with which the new stars, so far as has yet been observed, invariably
blaze forth. In almost every case it has been only two or three days
from the time that the existence of such an object became known until
it had attained nearly its full brightness. In fact, it would seem that
in the case of the star in Perseus, as in most other cases, the greater
part of the outburst took place within the space of twenty-four hours.
This suddenness and rapidity is exactly what would be the result of a
collision.
The most inexplicable feature of all is the rapid formation of a nebula
around this star. In the first photographs of the latter, the
appearance presented is simply that of an ordinary star. But, in the
course of three or four months, the delicate photographs taken at the
Lick Observatory showed that a nebulous light surrounded the star, and
was continually growing larger and larger. At first sight, there would
seem to be nothing extraordinary in this fact. Great masses of
intensely hot vapor, shining by their own light, would naturally be
thrown out from the star. Or, if the star had originally been
surrounded by a very rare nebulous fog or vapor, the latter would be
seen by the brilliant light emitted by the star. On this was based an
explanation offered by Kapteyn, which at first seemed very plausible.
It was that the sudden wave of light thrown out by the star when it
burst forth caused the illumination of the surrounding vapor, which,
though really at rest, would seem to expand with the velocity of light,
as the illumination reached more and more distant regions of the
nebula. This result may be made the subject of exact calculation. The
velocity of light is such as would make a circuit of the earth more
than seven times in a second. It would, therefore, go out from the star
at the rate of a million of miles in between five and six seconds. In
the lapse of one of our days, the light would have filled a sphere
around the star having a diameter more than one hundred and fifty times
the distance of the sun from the earth, and more than five times the
dimensions of the whole solar system. Continuing its course and
enlarging its sphere day after day, the sight presented to us would
have been that of a gradually expanding nebulous mass--a globe of faint
light continually increasing in size with the velocity of light.
The first sentiment the reader will feel on this subject is doubtless
one of surprise that the distance of the star should be so great as
this explanation would imply. Six months after the explosion, the globe
of light, as actually photographed, was of a size which would have been
visible to the naked eye only as a very minute object in the sky. Is it
possible that this minute object could have been thousands of times the
dimensions of our solar system?
To see how the question stands from this point of view, we must have
some idea of the possible distance of the new star. To gain this idea,
we must find some way of estimating distances in the universe. For a
reason which will soon be apparent, we begin with the greatest
structure which nature offers to the view of man. We all know that the
Milky Way is formed of countless stars, too minute to be individually
visible to the naked eye. The more powerful the telescope through which
we sweep the heavens, the greater the number of the stars that can be
seen in it. With the powerful instruments which are now in use for
photographing the sky, the number of stars brought to light must rise
into the hundreds of millions, and the greater part of these belong to
the Milky Way. The smaller the stars we count, the greater their
comparative number in the region of the Milky Way. Of the stars visible
through the telescope, more than one-half are found in the Milky Way,
which may be regarded as a girdle spanning the entire visible universe.
Of the diameter of this girdle we can say, almost with certainty, that
it must be more than a thousand times as great as the distance of the
nearest fixed star from us, and is probably two or three times greater.
According to the best judgment we can form, our solar system is situate
near the central region of the girdle, so that the latter must be
distant from us by half its diameter. It follows that if we can imagine
a gigantic pair of compasses, of which the points extend from us to
Alpha Centauri, the nearest star, we should have to measure out at
least five hundred spaces with the compass, and perhaps even one
thousand or more, to reach the region of the Milky Way.
With this we have to connect another curious fact. Of eighteen new
stars which have been observed to blaze forth during the last four
hundred years, all are in the region of the Milky Way. This seems to
show that, as a rule, they belong to the Milky Way. Accepting this very
plausible conclusion, the new star in Perseus must have been more than
five hundred times as far as the nearest fixed star. We know that it
takes light four years to reach us from Alpha Centauri. It follows that
the new star was at a distance through which light would require more
than two thousand years to travel, and quite likely a time two or three
times this. It requires only the most elementary ideas of geometry to
see that if we suppose a ray of light to shoot from a star at such a
distance in a direction perpendicular to the line of sight from us to
the star, we can compute how fast the ray would seem to us to travel.
Granting the distance to be only two thousand light years, the apparent
size of the sphere around the star which the light would fill at the
end of one year after the explosion would be that of a coin seen at a
distance of two thousand times its radius, or one thousand times its
diameter--say, a five-cent piece at the distance of sixty feet. But, as
a matter of fact, the nebulous illumination expanded with a velocity
from ten to twenty times as great as this.
The idea that the nebulosity around the new star was formed by the
illumination caused by the light of the explosion spreading out on all
sides therefore fails to satisfy us, not because the expansion of the
nebula seemed to be so slow, but because it was many times as swift as
the speed of light. Another reason for believing that it was not a mere
wave of light is offered by the fact that it did not take place
regularly in every direction from the star, but seemed to shoot off at
various angles.
Up to the present time, the speed of light has been to science, as well
as to the intelligence of our race, almost a symbol of the greatest of
possible speeds. The more carefully we reflect on the case, the more
clearly we shall see the difficulty in supposing any agency to travel
at the rate of the seeming emanations from the new star in Perseus.
As the emanation is seen spreading day after day, the reader may
inquire whether this is not an appearance due to some other cause than
the mere motion of light. May not an explosion taking place in the
centre of a star produce an effect which shall travel yet faster than
light? We can only reply that no such agency is known to science.
But is there really anything intrinsically improbable in an agency
travelling with a speed many times that of light? In considering that
there is, we may fall into an error very much like that into which our
predecessors fell in thinking it entirely out of the range of
reasonable probability that the stars should be placed at such
distances as we now know them to be.
Accepting it as a fact that agencies do exist which travel from sun to
planet and from star to star with a speed which beggars all our
previous ideas, the first question that arises is that of their nature
and mode of action. This question is, up to the present time, one which
we do not see any way of completely answering. The first difficulty is
that we have no evidence of these agents except that afforded by their
action. We see that the sun goes through a regular course of
pulsations, each requiring eleven years for completion; and we see
that, simultaneously with these, the earth's magnetism goes through a
similar course of pulsations. The connection of the two, therefore,
seems absolutely proven. But when we ask by what agency it is possible
for the sun to affect the magnetism of the earth, and when we trace the
passage of some agent between the two bodies, we find nothing to
explain the action. To all appearance, the space between the earth and
the sun is a perfect void. That electricity cannot of itself pass
through a vacuum seems to be a well-established law of physics. It is
true that electromagnetic waves, which are supposed to be of the same
nature with those of light, and which are used in wireless telegraphy,
do pass through a vacuum and may pass from the sun to the earth. But
there is no way of explaining how such waves would either produce or
affect the magnetism of the earth.