purpose of our coming together is the seemingly unending subdivision of
knowledge into specialties, many of which are becoming so minute and so
isolated that they seem to have no interest for any but their few
pursuers. Happily science itself has afforded a corrective for its own
tendency in this direction. The careful thinker will see that in these
seemingly diverging branches common elements and common principles are
coming more and more to light. There is an increasing recognition of
methods of research, and of deduction, which are common to large
branches, or to the whole of science. We are more and more recognizing
the principle that progress in knowledge implies its reduction to more
exact forms, and the expression of its ideas in language more or less
mathematical. The problem before the organizers of this Congress was,
therefore, to bring the sciences together, and seek for the unity which
we believe underlies their infinite diversity.
The assembling of such a body as now fills this hall was scarcely
possible in any preceding generation, and is made possible now only
through the agency of science itself. It differs from all preceding
international meetings by the universality of its scope, which aims to
include the whole of knowledge. It is also unique in that none but
leaders have been sought out as members. It is unique in that so many
lands have delegated their choicest intellects to carry on its work.
They come from the country to which our republic is indebted for a
third of its territory, including the ground on which we stand; from
the land which has taught us that the most scholarly devotion to the
languages and learning of the cloistered past is compatible with
leadership in the practical application of modern science to the arts
of life; from the island whose language and literature have found a new
field and a vigorous growth in this region; from the last seat of the
holy Roman Empire; from the country which, remembering a monarch who
made an astronomical observation at the Greenwich Observatory, has
enthroned science in one of the highest places in its government; from
the peninsula so learned that we have invited one of its scholars to
come and tells us of our own language; from the land which gave birth
to Leonardo, Galileo, Torricelli, Columbus, Volta--what an array of
immortal names!--from the little republic of glorious history which,
breeding men rugged as its eternal snow-peaks, has yet been the seat of
scientific investigation since the day of the Bernoullis; from the land
whose heroic dwellers did not hesitate to use the ocean itself to
protect it against invaders, and which now makes us marvel at the
amount of erudition compressed within its little area; from the nation
across the Pacific, which, by half a century of unequalled progress in
the arts of life, has made an important contribution to evolutionary
science through demonstrating the falsity of the theory that the most
ancient races are doomed to be left in the rear of the advancing
age--in a word, from every great centre of intellectual activity on the
globe I see before me eminent representatives of that world--advance in
knowledge which we have met to celebrate. May we not confidently hope
that the discussions of such an assemblage will prove pregnant of a
future for science which shall outshine even its brilliant past.
Gentlemen and scholars all! You do not visit our shores to find great
collections in which centuries of humanity have given expression on
canvas and in marble to their hopes, fears, and aspirations. Nor do you
expect institutions and buildings hoary with age. But as you feel the
vigor latent in the fresh air of these expansive prairies, which has
collected the products of human genius by which we are here surrounded,
and, I may add, brought us together; as you study the institutions
which we have founded for the benefit, not only of our own people, but
of humanity at large; as you meet the men who, in the short space of
one century, have transformed this valley from a savage wilderness into
what it is today--then may you find compensation for the want of a past
like yours by seeing with prophetic eye a future world-power of which
this region shall be the seat. If such is to be the outcome of the
institutions Which we are now building up, then may your present visit
be a blessing both to your posterity and ours by making that power one
for good to all man-kind. Your deliberations will help to demonstrate
to us and to the world at large that the reign of law must supplant
that of brute force in the relations of the nations, just as it has
supplanted it in the relations of individuals. You will help to show
that the war which science is now waging against the sources of
diseases, pain, and misery offers an even nobler field for the exercise
of heroic qualities than can that of battle. We hope that when, after
your all too-fleeting sojourn in our midst, you return to your own
shores, you will long feel the influence of the new air you have
breathed in an infusion of increased vigor in pursuing your varied
labors. And if a new impetus is thus given to the great intellectual
movement of the past century, resulting not only in promoting the
unification of knowledge, but in widening its field through new
combinations of effort on the part of its votaries, the projectors,
organizers and supporters of this Congress of Arts and Science will be
justified of their labors.
XVII
THE EVOLUTION OF ASTRONOMICAL KNOWLEDGE
[Footnote: Address at the dedication of the Flower Observatory,
University of Pennsylvania, May 12, 1897--Science, May 21, 1897]
Assembled, as we are, to dedicate a new institution to the promotion of
our knowledge of the heavens, it appeared to me that an appropriate and
interesting subject might be the present and future problems of
astronomy. Yet it seemed, on further reflection, that, apart from the
difficulty of making an adequate statement of these problems on such an
occasion as the present, such a wording of the theme would not fully
express the idea which I wish to convey. The so-called problems of
astronomy are not separate and independent, but are rather the parts of
one great problem, that of increasing our knowledge of the universe in
its widest extent. Nor is it easy to contemplate the edifice of
astronomical science as it now stands, without thinking of the past as
well as of the present and future. The fact is that our knowledge of
the universe has been in the nature of a slow and gradual evolution,
commencing at a very early period in human history, and destined to go
forward without stop, as we hope, so long as civilization shall endure.
The astronomer of every age has built on the foundations laid by his
predecessors, and his work has always formed, and must ever form, the
base on which his successors shall build. The astronomer of to-day may
look back upon Hipparchus and Ptolemy as the earliest ancestors of whom
he has positive knowledge. He can trace his scientific descent from
generation to generation, through the periods of Arabian and medieval
science, through Copernicus, Kepler, Newton, Laplace, and Herschel,
down to the present time. The evolution of astronomical knowledge,
generally slow and gradual, offering little to excite the attention of
the public, has yet been marked by two cataclysms. One of these is seen
in the grand conception of Copernicus that this earth on which we dwell
is not a globe fixed in the centre of the universe, but is simply one
of a number of bodies, turning on their own axes and at the same time
moving around the sun as a centre. It has always seemed to me that the
real significance of the heliocentric system lies in the greatness of
this conception rather than in the fact of the discovery itself. There
is no figure in astronomical history which may more appropriately claim
the admiration of mankind through all time than that of Copernicus.
Scarcely any great work was ever so exclusively the work of one man as
was the heliocentric system the work of the retiring sage of
Frauenburg. No more striking contrast between the views of scientific
research entertained in his time and in ours can be found than that
afforded by the fact that, instead of claiming credit for his great
work, he deemed it rather necessary to apologize for it and, so far as
possible, to attribute his ideas to the ancients.
A century and a half after Copernicus followed the second great step,
that taken by Newton. This was nothing less than showing that the
seemingly complicated and inexplicable motions of the heavenly bodies
were only special cases of the same kind of motion, governed by the
same forces, that we see around us whenever a stone is thrown by the
hand or an apple falls to the ground. The actual motions of the heavens
and the laws which govern them being known, man had the key with which
he might commence to unlock the mysteries of the universe.
When Huyghens, in 1656, published his Systema Saturnium, where he first
set forth the mystery of the rings of Saturn, which, for nearly half a
century, had perplexed telescopic observers, he prefaced it with a
remark that many, even among the learned, might condemn his course in
devoting so much time and attention to matters far outside the earth,
when he might better be studying subjects of more concern to humanity.
Notwithstanding that the inventor of the pendulum clock was, perhaps,
the last astronomer against whom a neglect of things terrestrial could
be charged, he thought it necessary to enter into an elaborate defence
of his course in studying the heavens. Now, however, the more distant
objects are in space--I might almost add the more distant events are in
time--the more they excite the attention of the astronomer, if only he
can hope to acquire positive knowledge about them. Not, however,
because he is more interested in things distant than in things near,
but because thus he may more completely embrace in the scope of his
work the beginning and the end, the boundaries of all things, and thus,
indirectly, more fully comprehend all that they include. From his
stand-point,
"All are but parts of one stupendous whole,
Whose body Nature is and God the soul."
Others study Nature and her plans as we see them developed on the
surface of this little planet which we inhabit, the astronomer would
fain learn the plan on which the whole universe is constructed. The
magnificent conception of Copernicus is, for him, only an introduction
to the yet more magnificent conception of infinite space containing a
collection of bodies which we call the visible universe. How far does
this universe extend? What are the distances and arrangements of the
stars? Does the universe constitute a system? If so, can we comprehend
the plan on which this system is formed, of its beginning and of its
end? Has it bounds outside of which nothing exists but the black and
starless depths of infinity itself? Or are the stars we see simply such
members of an infinite collection as happen to be the nearest our
system? A few such questions as these we are perhaps beginning to
answer; but hundreds, thousands, perhaps even millions, of years may
elapse without our reaching a complete solution. Yet the astronomer
does not view them as Kantian antinomies, in the nature of things
insoluble, but as questions to which he may hopefully look for at least
a partial answer.
The problem of the distances of the stars is of peculiar interest in
connection with the Copernican system. The greatest objection to this
system, which must have been more clearly seen by astronomers
themselves than by any others, was found in the absence of any apparent
parallax of the stars. If the earth performed such an immeasurable
circle around the sun as Copernicus maintained, then, as it passed from
side to side of its orbit, the stars outside the solar system must
appear to have a corresponding motion in the other direction, and thus
to swing back and forth as the earth moved in one and the other
direction. The fact that not the slightest swing of that sort could be
seen was, from the time of Ptolemy, the basis on which the doctrine of
the earth's immobility rested. The difficulty was not grappled with by
Copernicus or his immediate successors. The idea that Nature would not
squander space by allowing immeasurable stretches of it to go unused
seems to have been one from which medieval thinkers could not entirely
break away. The consideration that there could be no need of any such
economy, because the supply was infinite, might have been theoretically
acknowledged, but was not practically felt. The fact is that
magnificent as was the conception of Copernicus, it was dwarfed by the
conception of stretches from star to star so vast that the whole orbit
of the earth was only a point in comparison.
An indication of the extent to which the difficulty thus arising was
felt is seen in the title of a book published by Horrebow, the Danish
astronomer, some two centuries ago. This industrious observer, one of
the first who used an instrument resembling our meridian transit of the
present day, determined to see if he could find the parallax of the
stars by observing the intervals at which a pair of stars in opposite
quarters of the heavens crossed his meridian at opposite seasons of the
year. When, as he thought, he had won success, he published his
observations and conclusions under the title of Copernicus Triumphans.
But alas! the keen criticism of his successors showed that what he
supposed to be a swing of the stars from season to season arose from a
minute variation in the rate of his clock, due to the different
temperatures to which it was exposed during the day and the night. The
measurement of the distance even of the nearest stars evaded
astronomical research until Bessel and Struve arose in the early part
of the present century.
On some aspects of the problem of the extent of the universe light is
being thrown even now. Evidence is gradually accumulating which points
to the probability that the successive orders of smaller and smaller
stars, which our continually increasing telescopic power brings into
view, are not situated at greater and greater distances, but that we
actually see the boundary of our universe. This indication lends a
peculiar interest to various questions growing out of the motions of
the stars. Quite possibly the problem of these motions will be the
great one of the future astronomer. Even now it suggests thoughts and
questions of the most far-reaching character.
I have seldom felt a more delicious sense of repose than when crossing
the ocean during the summer months I sought a place where I could lie
alone on the deck, look up at the constellations, with Lyra near the
zenith, and, while listening to the clank of the engine, try to
calculate the hundreds of millions of years which would be required by
our ship to reach the star a Lyrae, if she could continue her course in
that direction without ever stopping. It is a striking example of how
easily we may fail to realize our knowledge when I say that I have
thought many a time how deliciously one might pass those hundred
millions of years in a journey to the star a Lyrae, without its
occurring to me that we are actually making that very journey at a
speed compared with which the motion of a steamship is slow indeed.
Through every year, every hour, every minute, of human history from the
first appearance of man on the earth, from the era of the builders of
the Pyramids, through the times of Caesar and Hannibal, through the
period of every event that history records, not merely our earth, but
the sun and the whole solar system with it, have been speeding their
way towards the star of which I speak on a journey of which we know
neither the beginning nor the end. We are at this moment thousands of
miles nearer to a Lyrae than we were a few minutes ago when I began
this discourse, and through every future moment, for untold thousands
of years to come, the earth and all there is on it will be nearer to a
Lyrae, or nearer to the place where that star now is, by hundreds of
miles for every minute of time come and gone. When shall we get there?
Probably in less than a million years, perhaps in half a million. We
cannot tell exactly, but get there we must if the laws of nature and
the laws of motion continue as they are. To attain to the stars was the
seemingly vain wish of an ancient philosopher, but the whole human race
is, in a certain sense, realizing this wish as rapidly as a speed of
ten miles a second can bring it about.
I have called attention to this motion because it may, in the not
distant future, afford the means of approximating to a solution of the
problem already mentioned--that of the extent of the universe.
Notwithstanding the success of astronomers during the present century
in measuring the parallax of a number of stars, the most recent
investigations show that there are very few, perhaps hardly more than a
score, of stars of which the parallax, and therefore the distance, has
been determined with any approach to certainty. Many parallaxes
determined about the middle of the nineteenth century have had to
disappear before the powerful tests applied by measures with the
heliometer; others have been greatly reduced and the distances of the
stars increased in proportion. So far as measurement goes, we can only
say of the distances of all the stars, except the few whose parallaxes
have been determined, that they are immeasurable. The radius of the
earth's orbit, a line more than ninety millions of miles in length, not
only vanishes from sight before we reach the distance of the great mass
of stars, but becomes such a mere point that when magnified by the
powerful instruments of modern times the most delicate appliances fail
to make it measurable. Here the solar motion comes to our help. This
motion, by which, as I have said, we are carried unceasingly through
space, is made evident by a motion of most of the stars in the opposite
direction, just as passing through a country on a railway we see the
houses on the right and on the left being left behind us. It is clear
enough that the apparent motion will be more rapid the nearer the
object. We may therefore form some idea of the distance of the stars
when we know the amount of the motion. It is found that in the great
mass of stars of the sixth magnitude, the smallest visible to the naked
eye, the motion is about three seconds per century. As a measure thus
stated does not convey an accurate conception of magnitude to one not
practised in the subject, I would say that in the heavens, to the
ordinary eye, a pair of stars will appear single unless they are
separated by a distance of 150 or 200 seconds. Let us, then, imagine
ourselves looking at a star of the sixth magnitude, which is at rest
while we are carried past it with the motion of six to eight miles per
second which I have described. Mark its position in the heavens as we
see it to-day; then let its position again be marked five thousand
years hence. A good eye will just be able to perceive that there are
two stars marked instead of one. The two would be so close together
that no distinct space between them could be perceived by unaided
vision. It is due to the magnifying power of the telescope, enlarging
such small apparent distances, that the motion has been determined in
so small a period as the one hundred and fifty years during which
accurate observations of the stars have been made.
The motion just described has been fairly well determined for what,
astronomically speaking, are the brighter stars; that is to say, those
visible to the naked eye. But how is it with the millions of faint
telescopic stars, especially those which form the cloud masses of the
Milky Way? The distance of these stars is undoubtedly greater, and the
apparent motion is therefore smaller. Accurate observations upon such
stars have been commenced only recently, so that we have not yet had
time to determine the amount of the motion. But the indication seems to
be that it will prove quite a measurable quantity and that before the
twentieth century has elapsed, it will be determined for very much
smaller stars than those which have heretofore been studied. A
photographic chart of the whole heavens is now being constructed by an
association of observatories in some of the leading countries of the
world. I cannot say all the leading countries, because then we should
have to exclude our own, which, unhappily, has taken no part in this
work. At the end of the twentieth century we may expect that the work
will be repeated. Then, by comparing the charts, we shall see the
effect of the solar motion and perhaps get new light upon the problem
in question.