truth is cast over the coming account of marvellous discoveries
by explaining in detail the construction of the imaginary
Herschelian instrument. Sir John is supposed to have had an
interesting conversation in England "with Sir David Brewster,
upon the merits of some ingenious suggestion by the latter, in
his article on optics in the Edinburgh Encyclopædia (p. 644), for
improvements in the Newtonian reflectors." The exact reference to
a particular page is here quite delightful. After some further
talk, "the conversation became directed to that all-invincible
enemy, the paucity of light in powerful magnifiers. After a few
moments' silent thought, Sir John diffidently inquired whether
it would not be possible to effect a _transfusion of artificial
light through the focal object of vision_! Sir David, somewhat
startled at the originality of the idea, paused awhile, and then
hesitatingly referred to the refrangibility of rays, and the angle
of incidence.... Sir John continued, 'Why cannot the illuminated
microscope, say the hydro-oxygen, be applied to render distinct,
and, if necessary, even to magnify the focal object?' Sir David
sprang from his chair in an ecstasy of conviction, and leaping
half-way to the ceiling, exclaimed, 'Thou art the man.' "This
absurd imaginary conversation contains nothing but an assemblage
of optical jargon, put together without the slightest intention of
conveying any intelligible meaning to scientific people. Yet it was
well adapted to deceive the public; and we should not be surprised
if it would be credited by many newspaper readers to-day.
The authors go on to explain how money was raised to build the
new instrument, and then describe Herschers embarkation and the
difficulties connected with transporting his gigantic machines
to the place selected for the observing station. "Sir John
accomplished the ascent to the plains by means of two relief
teams of oxen, of eighteen each, in about four days, and, aided
by several companies of Dutch boors [_sic_], proceeded at once to
the erecting of his gigantic fabric." The place really selected
by Herschel cannot be described better than in his own words,
contained in a genuine letter dated January 21, 1835: "A perfect
paradise in rich and magnificent mountain scenery, sheltered from
all winds.... I must reserve for my next all description of the
gorgeous display of flowers which adorn this splendid country, as
well as the astonishing brilliancy of the constellations." The
author of the hoax could have had no knowledge of Herschers real
location, as described in this letter.
The present writer can bear witness to the correctness of
Herschel's words. Feldhausen is truly an ideal secluded spot
for astronomical study. A small obelisk under the sheer cliff
of far-famed Table Mountain now marks the site of the great
reflecting telescope. Here Herschel carried on his scrutiny of the
Southern skies. He observed 1,202 double stars and 1,708 nebulæ
and clusters, of which only 439 were already known. He studied the
famous Magellanic clouds, and made the first careful drawings of
the "keyhole" nebula in the constellation Argo.
Very recent researches of the present royal astronomer at the Cape
have shown that changes of import have certainly taken place in
this nebula since Herschel's time, when a sudden blazing up of the
wonderful star Eta Argus was seen within the nebula. This object
has, perhaps, undergone more remarkable changes of light than
any other star in the heavens. It is as though there were some
vast conflagration at work, now blazing into incandescence, and
again sinking almost into invisibility. In 1843 Maclear estimated
the brilliancy of Eta to be about equal to that of Sirius, the
brightest star in the whole sky. Later it diminished in light,
and cannot be seen to-day with the naked eye, though the latest
telescopic observations indicate that it is again beginning to
brighten.
Such was Herschel's quiet study of his beloved science, in glaring
contrast to the supposed discoveries of the "Hoax." Here are a few
things alleged to have been seen on the moon. The first time the
instrument was turned upon our satellite "the field of view was
covered throughout its entire area with a beautifully distinct and
even vivid representation of basaltic rock." There were forests,
too, and water, "fairer shores never angels coasted on a tour
of pleasure. A beach of brilliant white sand, girt with wild
castellated rocks, apparently of green marble."
There was animal life as well; "we beheld continuous herds of
brown quadrupeds, having all the external characteristics of the
bison, but more diminutive than any species of the bos genus in our
natural history." There was a kind of beaver, that "carries its
young in its arms like a human being," and lives in huts. "From the
appearance of smoke in nearly all of them, there is no doubt of its
(the beaver's) being acquainted with the use of fire." Finally,
as was, of course, unavoidable, human creatures were discovered.
"Whilst gazing in a perspective of about half a mile, we were
thrilled with astonishment to perceive four successive flocks of
large-winged creatures, wholly unlike any kind of birds, descend
with a slow, even motion from the cliffs on the western side, and
alight upon the plain.... Certainly they were like human beings,
and their attitude in walking was both erect and dignified."
We have not space to give more extended extracts from the hoax,
but we think the above specimens will show how deceptive the whole
thing was. The rare reprint from which we have extracted our
quotations contains also some interesting "Opinions of the American
Press Respecting the Foregoing Discovery." The _Daily Advertiser_
said: "No article, we believe, has appeared for years, that will
command so general a perusal and publication. Sir John has added
a stock of knowledge to the present age that will immortalize his
name and place it high on the page of science." The _Mercantile
Advertiser_ said: "Discoveries in the Moon.--We commence to-day
the publication of an interesting article which is stated to have
been copied from the Edinburgh _Journal of Science_, and which
made its first appearance here in a contemporary journal of this
city. It appears to carry intrinsic evidence of being an authentic
document." Many other similar extracts are given. The New York
_Evening Post_ did not fall into the trap. The _Evening Post's_
remarks were as follows: "It is quite proper that the _Sun_ should
be the means of shedding so much light on the _Moon_. That there
should be winged people in the moon does not strike us as more
wonderful than the existence of such a race of beings on the
earth; and that there does or did exist such a race rests on the
evidence of that most veracious of voyagers and circumstantial of
chroniclers, Peter Wilkins, whose celebrated work not only gives an
account of the general appearance and habits of a most interesting
tribe of flying Indians, but also of all those more delicate and
engaging traits which the author was enabled to discover by reason
of the conjugal relations he entered into with one of the females
of the winged tribe."
We shall limit our extracts from the contemporary press to the few
quotations here given, hoping that enough has been said to direct
attention once more to that important subject, the Possibility of
Being Deceived.
THE SUN'S DESTINATION
Three generations of men have come and gone since the Marquis
de Laplace stood before the Academy of France and gave his
demonstration of the permanent stability of our solar system. There
was one significant fault in Newton's superbly simple conception of
an eternal law governing the world in which we live. The labors of
mathematicians following him had shown that the planets must trace
out paths in space whose form could be determined in advance with
unerring certainty by the aid of Newton's law of gravitation. But
they proved just as conclusively that these planetary orbits, as
they are called, could not maintain indefinitely the same shapes or
positions. Slow indeed might be the changes they were destined to
undergo; slow, but sure, with that sureness belonging to celestial
science alone. And so men asked: Has this magnificent solar system
been built upon a scale so grand, been put in operation subject
to a law sublime in its very simplicity, only to change and change
until at length it shall lose every semblance of its former self,
and end, perhaps, in chaos or extinction?
Laplace was able to answer confidently, "No." Nor was his answer
couched in the enthusiastic language of unbalanced theorists who
work by the aid of imagination alone. Based upon the irrefragable
logic of correct mathematical reasoning, and clad in the sober garb
of mathematical formulæ, his results carried conviction to men of
science the world over. So was it demonstrated that changes in our
solar system are surely at work, and shall continue for nearly
countless ages; yet just as surely will they be reversed at last,
and the system will tend to return again to its original form and
condition. The objection that the Newtonian law meant ultimate
dissolution of the world was thus destroyed by Laplace. From that
day forward the law of gravitation has been accepted as holding
sway over all phenomena visible within our planetary world.
The intricacies of our own solar system being thus illumined, the
restless activity of the human intellect was stimulated to search
beyond for new problems and new mysteries. Even more fascinating
than the movements of our sun and planets are all those questions
that relate to the clustered stellar congeries hanging suspended
within the deep vault of night. Does the same law of gravitation
cast its magic spell over that hazy cloud of Pleiades, binding
them, like ourselves, with bonds indissoluble? Who shall answer,
yes or no? We can only say that astronomers have as yet but stepped
upon the threshold of the universe, and fixed the telescope's great
eye upon that which is within.
Let us then begin by reminding the reader what is meant by the
Newtonian law of gravitation. It appears all things possess the
remarkable property of attracting or pulling each other. Newton
declared that all substances, solid, liquid, or even gaseous--from
the massive cliff of rock down to the invisible air--all matter can
no more help pulling than it can help existing. His law further
formulates certain conditions governing the manner in which this
gravitational attraction is exerted; but these are mere matters of
detail; interest centres about the mysterious fact of attraction
itself. How can one thing pull another with no connecting link
through which the pull can act? Just here we touch the point
that has never yet been explained. Nature withholds from science
her ultimate secrets. They that have pondered longest, that have
descended farthest of all men into the clear well of knowledge,
have done so but to sound the depths beyond, never touching bottom.
This inability of ours, to give a good physical explanation of
gravitation, has led certain makers of paradoxes to doubt or even
deny that there is any such thing. But, fortunately, we have a
simple laboratory experiment that helps us. Unexplained it may
ever remain, but that there can be attraction between physical
objects connected by no visible link is proved by the behavior
of an ordinary magnet. Place a small piece of steel or iron near
a magnetized bar, and it will at once be so strongly attracted
that it will actually fly to the magnet. Anyone who has seen this
simple experiment can never again deny the possibility, at least,
of the law of attraction as stated by Newton. Its possibility
once admitted, the fact that it can predict the motions of all
the planets, even down to their minutest details, transforms the
possibility of its truth into a certainty as strong as any human
certainty can ever be.
But this demonstration of Newton's law is limited strictly to
the solar system itself. We may, indeed, reason by analogy, and
take for granted that a law which holds within our immediate
neighborhood is extremely likely to be true also of the entire
visible universe. But men of science are loath to reason thus; and
hence the fascination of researches in cosmic astronomy. Analogy
points out the path. The astronomer is not slow to follow; but he
seeks ever to establish upon incontrovertible evidence those truths
which at first only his daring imagination had led him to half
suspect.
If we are to extend the law of gravitation to the utmost, we must
be careful to consider the law itself in its most complete form.
A heavenly body like the sun is often said to govern the motions
of its family of planets; but such a statement is not strictly
accurate. The governing body is no despot; 'tis an abject slave of
law and order, as much as the tiniest of attendant planets. The
action of gravitation is mutual, and no cosmic body can attract
another without being itself in turn subject to that other's
gravitational action.
If there were in our solar system but two bodies, sun and planet,
we should find each one pursuing a path in space under the
influence of the other's attraction. These two paths or orbits
would be oval, and if the sun and planet were equally massive, the
orbits would be exactly alike, both in shape and size. But if the
sun were far larger than the planet, the orbits would still be
similar in form, but the one traversed by the larger body would be
small. For it is not reasonable to expect a little planet to keep
the big sun moving with a velocity as great as that derived by
itself from the attraction of the larger orb.
Whenever the preponderance of the larger body is extremely great,
its orbit will be correspondingly insignificant in size. This is
in fact the case with our own sun. So massive is it in comparison
with the planets that the orbit is too small to reveal its actual
existence without the aid of our most refined instruments. The path
traced out by the sun's centre would not fill a space as large as
the sun's own bulk. Nevertheless, true orbital motion is there.
So we may conclude that as a necessary consequence of the law of
gravitation every object within the solar system is in motion. To
say that planets revolve about the sun is to neglect as unimportant
the small orbit of the sun itself. This may be sufficiently
accurate for ordinary purposes; but it is unquestionably necessary
to neglect no factor, however small, if we propose to extend our
reasoning to a consideration of the stellar universe. For we shall
then have to deal with systems in which the planets are of a size
comparable with the sun; and in such systems all the orbits will
also be of comparatively equal importance.
Mathematical analysis has derived another fact from discussion
of the law of gravitation which, perhaps, transcends in simple
grandeur everything we have as yet mentioned. It matters not how
great may be the number of massive orbs threading their countless
interlacing curved paths in space, there yet must be in every
cosmic system one single point immovable. This point is called the
Centre of Gravity. If it should so happen that in the beginning of
things, some particle of matter were situated at this centre, then
would that atom ever remain unmoved and imperturbable throughout
all the successive vicissitudes of cosmic evolution. It is doubtful
whether the mind of man can form a conception of anything grander
than such an immovable atom within the mysterious intricacies of
cosmic motion.
But in general, we cannot suppose that the centres of gravity in
the various stellar systems are really occupied by actual physical
bodies. The centre may be a mere mathematical point in space,
situated among the several bodies composing the system, but,
nevertheless, endowed, in a certain sense, with the same remarkable
property of relative immobility.
Having thus defined the centre of gravity in its relation to the
constituent parts of any cosmic system, we can pass easily to its
characteristic properties in connection with the inter-relation of
stellar systems with one another. It can be proved mathematically
that our solar system will pull upon distant stars just as though
the sun and all the planets were concentrated into one vast sphere
having its centre in the centre of gravity of the whole. It is this
property of the centre of gravity which makes it pre-eminently
important in cosmic researches. For, while we know that centre to
be at rest relatively to all the planets in the system, it may,
nevertheless, in its quality as a sort of concentrated essence of
them all, be moving swiftly through space under the pull of distant
stars. In that case, the attendant bodies will go with it--but they
will pursue their evolutions within the system, all unconscious
that the centre of gravity is carrying them on a far wider circuit.
What is the nature of that circuit? This question has been for
many years the subject of earnest study by the clearest minds
among astronomers. The greatest difficulty in the way is the
comparatively brief period during which men have been able to
make astronomical observations of precision. Space and time are
two conceptions that transcend the powers of definition possessed
by any man. But we can at least form a notion of how vast is the
extent of time, if we remember that the period covered by man's
written records is registered but as a single moment upon the
great revolving dial of heaven's dome. One hundred and fifty years
have elapsed since James Bradley built the foundations of modern
sidereal astronomy upon his masterly series of observations at the
Royal Observatory of Greenwich, in England. Yet so slowly do the
movements of the stars unroll themselves upon the firmament, that
even to this day no one of them has been seen by men to trace out
more than an infinitesimal fraction of its destined path through
the voids of space.
Travellers upon a railroad cannot tell at any given moment whether
they are moving in a straight line, or whether the train is
turning upon some curve of huge size. The St. Gothard railway
has several so-called "corkscrew" tunnels, within which the rails
make a complete turn in a spiral, the train finally emerging from
the tunnel at a point almost vertically over the entrance. In this
way the train is lifted to a higher level. Passengers are wont to
amuse themselves while in these tunnels by watching the needle of
an ordinary pocket-compass. This needle, of course, always points
to the north; and as the train turns upon its curve, the needle
will make a complete revolution. But the passenger could not know
without the compass that the train was not moving in a perfectly
straight line. Just so we passengers on the earth are unaware of
the kind of path we are traversing, until, like the compass, the
astronomer's instruments shall reveal to us the truth.
But as we have seen, astronomical observations of precision have
not as yet extended through a period of time corresponding to the
few minutes during which the St. Gothard traveller watches the
compass. We are still in the dark, and do not know as yet whether
mankind shall last long enough upon the earth to see the compass
needle make its revolution. We are compelled to believe that the
motion in space of our sun is progressing upon a curved path; but
so far as precise observations allow us to speak, we can but say
that we have as yet moved through an infinitesimal element only of
that mighty curve. However, we know the point upon the sky toward
which this tiny element of our path is directed, and we have an
approximate knowledge of the speed at which we move.
More than a century ago Sir William Herschel was able to fix
roughly what we call the apex of the sun's way in space, or the
point among the stars toward which that way is for the moment
directed. We say for the moment, but we mean that moment of which
Bradley saw the beginning in 1750, and upon whose end no man of
those now living shall ever look. Herschel found that a comparison
of old stellar observations seemed to indicate that the stars in a
certain part of the sky were opening out, as it were, and that the
constellations in the opposite part of the heavens seemed to be
drawing in, or becoming smaller. There can be but one reasonable
explanation of this. We must be moving toward that part of the sky
where the stars are separating. Just so a man watching a regiment
of soldiers approaching, will see at first only a confused body of
men; but as they come nearer, the individual soldiers will seem to
separate, until at length each one is seen distinct from all the
others.
Herschel fixed the position of the apex at a point in the
constellation Hercules. The most recent investigations of Newcomb
and others have, on the whole, verified Herschel's conclusions.
With the intuitive power of rare genius, Herschel had been able to
sift truth out of error. The observational data at his disposal
would now be called rude, but they disclosed to the scrutiny of
his acute understanding the germ of truth that was in them. Later
investigators have increased the precision of our knowledge, until
we can now say that the present direction of the solar motion is
known within very narrow limits. A tiny circle might be drawn on
the sky, to which an astronomer might point his hand and say:
"Yonder little circle contains the goal toward which the sun and
planets are hastening to-day." Even the speed of this motion has
been subjected to measurement, and found to be about ten miles per
second.
The objective point and the rate of motion thus stated, exact
science holds her peace. Here genuine knowledge stops; and we can
proceed further only by the aid of that imagination which men of
science need to curb at every moment. But let no one think that the
sun will ever reach the so-called apex. To do so would mean cosmic
motion upon a straight line, while every consideration of celestial
mechanics points to motion upon a curve. When shall we turn
sufficiently upon that curve to detect its bending? 'Tis a problem
we must leave as a rich heritage to later generations that are to
follow us. The visionary theorist's notion of a great central sun,
controlling our own sun's way in space, must be dismissed as far
too daring. But for such a central sun we may substitute a central
centre of gravity belonging to a great system of which our sun
is but an insignificant member. Then we reach a conception that
has lost nothing in the grandeur of its simplicity, and is yet
in accord with the probabilities of sober mechanical science. We
cease to be a lonely world, and stretch out the bonds of a common
relationship to yonder stars within the firmament.
INDEX
PAGE
Airy, Astronomer Royal, 1
Allis, photographs comet, 101
Andromeda nebula, 28
temporary star, 28, 29, 45
Apex, of solar motion, explained, 221
Aquila, constellation, temporary star in, 40
Arctic regions, position of pole in, 194
Argo, constellation, variable star in, 205
Association, international geodetic, 139
Asteroids, first discovery by Piazzi, 59, 106
discovery by photography, 64
group of, 63
photography of, invented by Wolf, 104
Astronomer, royal, 1
working, description of, 152
ASTRONOMER'S POLE, THE, 184
Astronomy, journalistic, 176
practical uses of, 112
Atmospheric refraction, explained, 193
Axis, of figure of the earth, 136
of rotation of the earth, 136
polar, of telescope, 173
Barnard, discovers satellite of Jupiter, 51
Bessel, measures Pleiades, 15
Bond, discovers crape ring of Saturn, 144
Bradley, observes at Greenwich, 219
Brahe, Tycho, his temporary star, 40
Bruce, endows polar photography, 197
Campbell, observes Pole-star, 18
Cape of Good Hope, observatory, photography at, 101
telescope, 170, 174
_Capriccio_, Galileo's, 55
Cassini, shows Saturn's rings to be double, 144
Cassiopeia, temporary star in, 40
Celestial pole, 184
Central sun theory, 223
Centre of gravity, 217
Chart-room, on ship-board, 5
Chronometer, invention of, 8
Circle, meridian, explained, 189
Clerk Maxwell, discusses Saturn's rings, 146