in the list of known "temporaries" appeared. It possessed very
great light-giving power, being surpassed in brilliancy by only
about a score of stars in all the heavens. It retained a maximum
luminosity only three or four days, and in less than two months
had diminished to a point somewhere between the ninth and tenth
"magnitudes." In other words, from a conspicuous star, visible to
the naked eye, it had passed beyond the power of anything less than
a good telescope. Fortunately, we had excellent star-catalogues
before 1866. These were at once searched, and it was possible to
settle quite definitely that a star of about the ninth or tenth
magnitude had really existed before 1866 at precisely the same
point occupied by the new one. Needless to say, observations were
made of the new star itself, and afterward compared with later
observations of the faint one that still occupies its place. These
render quite certain the identity of the temporary bright star with
the faint ones that preceded and followed it.
Such results, on the one hand, offer an excellent vindication
of the painstaking labor expended on the construction of
star-catalogues, and, on the other, serve to elucidate the mystery
of temporary stars. Nothing can be more plausible than to explain
by analogy those cases in which no previous or subsequent existence
has been observed. It is merely necessary to suppose that, instead
of varying from the ninth or tenth magnitude, other temporary
objects have begun and ended with the twentieth; for the twentieth
magnitude would be beyond the power of our best instruments.
Nor is the star of 1866 an isolated instance. Ten years later, in
1876, a temporary star blazed up to about the second magnitude, and
returned to invisibility, so far as the naked eye is concerned,
within a month, having retained its greatest brilliancy only one
or two days. This star is still visible as a tiny point of light,
estimated to be of the fifteenth magnitude. Whether it existed
prior to its sudden outburst can never be known, because we do not
possess catalogues including the generality of stars as faint as
this one must have been. But at all events, the continued existence
of the object helps to place the temporary stars in the class of
variables.
The next star, already mentioned under "nebula," was first seen
in 1885. It was in one respect the most remarkable of all, for
it appeared almost in the centre of the great nebula in the
constellation Andromeda. It was never very bright, reaching only
the sixth magnitude or thereabouts, was observed during a period of
only six months, and at the end of that time had faded beyond the
reach of our most powerful glasses. It is a most impressive fact
that this event occurred within the nebula. Whatever may be the
nature of the explosive catastrophe to which the temporary stars
owe their origin, we can now say with certainty that not even those
vast elemental luminous clouds men call nebulæ are free from danger.
The last outburst on our records was first noticed February 22,
1901. The star appeared in the constellation Perseus, and soon
reached the first magnitude, surpassing almost every other star
in the sky. It has been especially remarkable in that it has
become surrounded by a nebulous mass in which are several bright
condensations or nuclei; and these seem to be in very rapid motion.
The star is still under observation (January, 1902).
GALILEO
Among the figures that stand out sharply upon the dim background
of old-time science, there is none that excites a keener interest
than Galileo. Most people know him only as a distinguished man
of learning; one who carried on a vigorous controversy with the
Church on matters scientific. It requires some little study, some
careful reading between the lines of astronomical history, to gain
acquaintance with the man himself. He had a brilliant, incisive
wit; was a genuine humorist; knew well and loved the amusing side
of things; and could not often forego a sarcastic pleasantry, or
deny himself the pleasure of argument. Yet it is more than doubtful
if he ever intended impertinence, or gave willingly any cause of
quarrel to the Church.
His acute understanding must have seen that there exists no real
conflict between science and religion; for time, in passing, has
made common knowledge of this truth, as it has of many things once
hidden. When we consider events that occurred three centuries
ago, it is easy to replace excited argument with cool judgment;
to remember that those were days of violence and cruelty; that
public ignorance was of a density difficult to imagine to-day;
and that it was universally considered the duty of the Church to
assume an authoritative attitude upon many questions with which she
is not now required to concern herself in the least. Charlatans,
unbalanced theorists, purveyors of scientific marvels, were all
liable to be passed upon definitely by the Church, not in a spirit
of impertinent interference, but simply as part of her regular
duties.
If the Church's judgment in such matters was sometimes erroneous;
if her interference now and again was cruel, the cause must be
sought in the manners and customs of the time, when persecution
rioted in company with ignorance, and violence was the law. Perhaps
even to-day it would not be amiss to have a modern scientific board
pass authoritatively upon novel discoveries and inventions, so as
to protect the public against impostors as the Church tried to do
of old.
Galileo was born at Pisa in 1564, and his long life lasted
until 1642, the very year of Newton's birth. His most important
scientific discoveries may be summed up in a few words; he was the
first to use a telescope for examining the heavenly bodies; he
discovered mountains on the moon; the satellites of Jupiter; the
peculiar appearance of Saturn which Huygens afterward explained as
a ring surrounding the ball of the planet; and, finally, he found
black spots on the sun's disk. These discoveries, together with his
remarkable researches in mechanical science, constitute Galileo's
claim to immortality as an investigator. But, as we have said, it
is not our intention to consider his work as a series of scientific
discoveries. We shall take a more interesting point of view, and
deal with him rather as a human being who had contracted the habit
of making scientific researches.
What must have been his feelings when he first found with his "new"
telescope the satellites of Jupiter? They were seen on the night
of January 7, 1610. He had already viewed the planet through his
earlier and less powerful glass, and was aware that it possessed
a round disk like the moon, only smaller. Now he saw also three
objects that he took to be little stars near the planet. But on the
following night, as he says, "drawn by what fate I know not," the
tube was again turned upon the planet. The three small stars had
changed their positions, and were now all situated to the west of
Jupiter, whereas on the previous night two had been on the eastern
side. He could not explain this phenomenon, but he recognized that
there was something peculiar at work. Long afterward, in one of
his later works, translated into quaint old English by Salusbury,
he declared that "one sole experiment sufficeth to batter to the
ground a thousand probable Arguments." This was already the guiding
principle of his scientific activity, a principle of incomparable
importance, and generally credited to Bacon. Needless to say,
Jupiter was now examined every night.
The 9th was cloudy, but on the 10th he again saw his little stars,
their number now reduced to two. He guessed that the third was
behind the planet's disk. The position of the two visible ones was
altogether different from either of the previous observations. On
the 11th he became sure that what he saw was really a series of
satellites accompanying Jupiter on his journey through space, and
at the same time revolving around him. On the 12th, at 3 A.M.,
he actually saw one of the small objects emerge from behind the
planet; and on the 13th he finally saw four satellites. Two hundred
and eighty-two years were destined to pass away before any human
eye should see a fifth. It was Barnard in 1892 who followed Galileo.
To understand the effect of this discovery upon Galileo requires
a person who has himself watched the stars, not, as a dilettante,
seeking recreation or amusement, but with that deep reverence
that comes only to him who feels--nay, knows--that in the moment
of observation just passed he too has added his mite to the great
fund of human knowledge. Galileo's mummied forefinger still points
toward the stars from its little pedestal of wood in the _Museo_
at Florence, a sign to all men that he is unforgotten. But Galileo
knew on that 11th of January, 1610, that the memory of him would
never fade; that the very music of the spheres would thenceforward
be attuned to a truer note, if any would but hearken to the Jovian
harmony. For he recognized at once that the visible revolution of
these moons around Jupiter, while that planet was himself visibly
travelling through space, must deal its death-blow to the old
Ptolemaic system of the universe. Here was a great planet, the
centre of a system of satellites, and yet not the centre of the
universe. Surely, then, the earth, too, might be a mere planet like
Jupiter, and not the supposed motionless centre of all things.
The satellite discovery was published in 1610 in a little book
called "Sidereus Nuncius," usually translated "The Sidereal
Messenger." It seems to us, however, that the word "messenger" is
not strong enough; surely in Papal Italy a _nuncius_ was more than
a mere messenger. He was clothed with the very highest authority,
and we think it probable that Galileo's choice of this word in
the title of his book means that he claimed for himself similar
authority in science. At all events, the book made him at once a
great reputation and numerous enemies.
But it was not until 1616 that the Holy Office (Inquisition) issued
an edict ordering Galileo to abandon his opinion that the earth
moved, and at the same time placed Copernicus's _De Revolutionibus_
and two other books advocating that doctrine on the "Index Librorum
Prohibitorum," or list of books forbidden by the Church. These
volumes remained in subsequent editions of the "Index" down to
1821, but they no longer appear in the edition in force to-day.
Galileo's most characteristic work is entitled the "Dialogue on the
Two Chief Systems of the World." It was not published until 1632,
although the idea of the book was conceived many years earlier.
In it he gave full play to his extraordinary powers as a true
humorist, a _fine lame_ among controversialists, and a genuine man
of science, valuing naked truth above all other things. As may
be imagined, it was no small matter to obtain the authorities'
consent to this publication. Galileo was already known to hold
heretical opinions, and it was suspected that he had not laid them
aside when commanded to do so by the edict of 1616. But perhaps
Galileo's introduction to the "Dialogue" secured the censor's
_imprimatur_; it is even suspected that the Roman authorities
helped in the preparation of this introduction. Fortunately, we
have a delightful contemporary translation into English, by Thomas
Salusbury, printed at London by Leybourne in 1661. We have already
quoted from this translation, and now add from the same work part
of Galileo's masterly preface to the "Dialogue":
"Judicious reader, there was published some years since in _Rome_
a salutiferous Edict, that, for the obviating of the dangerous
Scandals of the Present Age, imposed a reasonable Silence upon the
Pythagorean (Copernican) opinion of the Mobility of the Earth.
There want not such as unadvisedly affirm, that the Decree was not
the production of a sober Scrutiny, but of an ill-formed passion;
and one may hear some mutter that Consultors altogether ignorant
of Astronomical observations ought not to clipp the wings of
speculative wits with rash prohibitions."
Galileo first states his own views, and then pretends that he will
oppose them. He goes on to say that he believes in the earth's
immobility, and takes "the contrary only for a mathematical
_Capriccio_," as he calls it; something to be considered, because
possessing an academical interest, but on no account having a real
existence. Of course any one (even a censor) ought to be able to
see that it is the Capriccio, and not its opposite, that Galileo
really advocates. Three persons appear in the "Dialogue": Salviati,
who believes in the Copernican system; Simplicio, of suggestive
name, who thinks the earth cannot move; and, finally, Sagredus,
a neutral gentleman of humorous propensities, who usually begins
by opposing Salviati, but ends by being convinced. He then helps
to punish poor Simplicio, who is one of those persons apparently
incapable of comprehending a reasonable argument. Here is an
interesting specimen of the "Dialogue" taken from Salusbury's
translation: Salviati refers to the argument, then well known, that
the earth cannot rotate on its axis, "because of the impossibility
of its moving long without wearinesse." Sagredus replies: "There
are some kinds of animals which refresh themselves after wearinesse
by rowling on the earth; and that therefore there is no need
to fear that the Terrestrial Globe should tire, nay, it may be
reasonably affirmed that it enjoyeth a perpetual and most tranquil
repose, keeping itself in an eternal rowling." Salviati's comment
on this sally is, "You are too tart and satyrical, Sagredus."
There is no doubt that the "Dialogue" finished the Ptolemaic
theory, and made that of Copernicus the only possible one. At
all events, it brought about the well-known attack upon Galileo
from the authorities of the Holy Office. We shall not recount
the often-told tale of his recantation. He was convicted (very
rightly) of being a Copernican, and was forced to abjure that
doctrine. Galileo's life may be summed up as one of those through
which the world has been made richer. A clean-cutting analytic
wit, never becoming dull: heated again and again in the fierce
blaze of controversy, it was allowed to cool only that it might
acquire a finer temper, to pierce with fatal certainty the smallest
imperfections in the armor of his adversaries.
THE PLANET OF 1898
The discovery of a new and important planet usually receives
more immediate popular attention and applause than any other
astronomical event. Philosophers are fond of referring to our
solar system as a mere atom among the countless universes that
seem to be suspended within the profound depths of space. They are
wont to point out that this solar system, small and insignificant
as a whole in comparison with many of the stellar worlds, is,
nevertheless, made up of a large number of constituent planets; and
these in turn are often accompanied with still smaller satellites,
or moons. Thus does Nature provide worlds within worlds, and it is
not surprising that public attention should be at once attracted
by any new member of our sun's own special family of planets. The
ancients were acquainted with only five of the bodies now counted
as planets, viz.: Mercury, Venus, Mars, Jupiter, and Saturn. The
dates of their discovery are lost in antiquity. To these Uranus was
added in 1781 by a brilliant effort of the elder Herschel. We are
told that intense popular excitement followed the announcement of
Herschel's first observation: he was knighted and otherwise honored
by the English King, and was enabled to lay a secure foundation for
the future distinguished astronomical reputation of his family.
Herschel's discovery quickened the restless activity of
astronomers. Persistent efforts were made to sift the heavens
more and more closely, with the strengthened hope of adding still
further to our planetary knowledge. An association of twenty-four
enthusiastic German astronomers was formed for the express purpose
of hunting planets. But it fell to the lot of an Italian, Piazzi,
of Palermo, to find the first of that series of small bodies now
known as the asteroids or minor planets. He made the discovery at
the very beginning of our century, January 1, 1801.
But news travelled slowly in those days, and it was not until
nearly April that the German observers heard from Piazzi. In the
meantime, he had himself been prevented by illness from continuing
his observations. Unfortunately, the planet had by this time moved
so near the sun, on account of its own motions and those of the
earth, that it could no longer be observed. The bright light of
the sun made observations of the new body impossible; and it was
feared that, owing to lack of knowledge of the planet's orbit,
astronomers would be unable to trace it. So there seemed, indeed,
to be danger of an almost irreparable loss to science. But in
scientific, as in other human emergencies, someone always appears
at the proper moment. A very young mathematician at Göttingen,
named Gauss, attacked the problem, and was able to devise a method
of predicting the future course of the planet on the sky, using
only the few observations made by Piazzi himself. Up to that time
no one had attempted to compute a planetary orbit, unless he had
at his disposal a series of observations extending throughout the
whole period of the planet's revolution around the sun. But the
Piazzi planet offered a new problem in astronomy. It had become
imperatively necessary to obtain an orbit from a few observations
made at nearly the same date. Gauss's work was signally triumphant,
for the planet was actually found in the position predicted by him,
as soon as a change in the relative places of the planet and earth
permitted suitable observations to be made.
But after all, Piazzi's planet belongs to a class of quite small
bodies, and is by no means as interesting as Herschel's discovery,
Uranus. Yet even this must be relegated to second rank among
planetary discoveries. On September 23, 1846, the telescope of the
Berlin Observatory was directed to a certain point on the sky for a
very special reason. Galle, the astronomer of Berlin, had received
a letter from Leverrier, of Paris, telling him that if he would
look in a certain direction he would detect a new and large planet.
Leverrier's information was based upon a mathematical calculation.
Seated in his study, with no instruments but pen and paper, he
had slowly figured out the history of a world as yet unseen.
Tiny discrepancies existed in the observed motions of Herschel's
planet Uranus. No man had explained their cause. To Leverrier's
acute understanding they slowly shaped themselves into the
possible effects of attraction emanating from some unknown planet
exterior to Uranus. Was it conceivable that these slight tremulous
imperfections in the motion of a planet could be explained in this
way? Leverrier was able to say confidently, "Yes." But we may rest
assured that Galle had but small hopes that upon his eye first, of
all the myriad eyes of men, would fall a ray of the new planet's
light. Careful and methodical, he would neglect no chance of
advancing his beloved science. He would look.
Only one who has himself often seen the morning's sunrise put an
end to a night's observation of the stars can hope to appreciate
what Galle's feelings must have been when he saw the planet. To his
trained eye it was certainly recognizable at once. And then the
good news was sent on to Paris. We can imagine Leverrier, the cool
calculator, saying to himself: "Of course he found it. It was a
mathematical certainty." Nevertheless, his satisfaction must have
been of the keenest. No triumphs give a pleasure higher than those
of the intellect. Let no one imagine that men who make researches
in the domain of pure science are under-paid. They find their
reward in pleasure that is beyond any price.
The Leverrier planet was found to be the last of the so-called
major planets, so far as we can say in the present state of
science. It received the name Neptune. Observers have found no
other member of the solar system comparable in size with such
bodies as Uranus and Neptune. More than one eager mathematician has
tried to repeat Leverrier's achievement, but the supposed planet
was not found. It has been said that figures never lie; yet such is
the case only when the computations are correctly made. People are
prone to give to the work of careless or incompetent mathematicians
the same degree of credence that is really due only to masters of
the craft. It requires the test of time to affix to any man's work
the stamp of true genius.
While, then, we have found no more large planets, quite a group of
companions to Piazzi's little one have been discovered. They are
all small, probably never exceeding about 400 miles in diameter.
All travel around the sun in orbits that lie wholly within that
of Jupiter and are exterior to that of Mars. The introduction of
astronomical photography has given a tremendous impetus to the
discovery of these minor planets, as they are called. It is quite
interesting to examine the photographic process by which such
discoveries are made possible and even easy. The matter will not
be difficult to understand if we remember that all the planets are
continually changing their places among the other stars. For the
planets travel around the sun at a comparatively small distance.
The great majority of the stars, on the contrary, are separated
from the sun by an almost immeasurable space. As a result, they do
not seem to move at all among themselves, and so we call them fixed
stars: they may, indeed, be in motion, but their great distance
prevents our detecting it in a short period of time.
Now, stellar photographs are made in much the same way as ordinary
portraits. Only, instead of using a simple camera, the astronomer
exposes his photographic plate at the eye-end of a telescope. The
sensitive surface of the plate is substituted for the human eye. We
then find on the picture a little dot corresponding to every star
within the photographed region of the sky. But, as everyone knows,
the turning of the earth on its axis makes the whole heavens,
including the sun, moon, and stars, rise and set every day. So the
stars, when we photograph them, are sure to be either climbing up
in the eastern sky or else slowly creeping down in the western. And
that makes astronomical photography very different from ordinary
portrait work.
The stars correspond to the sitter, but they don't sit still.
For this reason it is necessary to connect the telescope with a
mechanical contrivance which makes it turn round like the hour-hand
of an ordinary clock. The arrangement is so adjusted that the
telescope, once aimed at the proper object in the sky, will move
so as to remain pointed exactly the same during the whole time of
the photographic exposure. Thus, while the light of any star is
acting on the plate, such action will be continuous at a single
point. Consequently, the finished picture will show the star as a
little dot; while without this arrangement, the star would trail
out into a line instead of a dot. Now we have seen that the planets
are all moving slowly among the fixed stars. So if we make a star
photograph in a part of the sky where a planet happens to be, the
planet will make a short line on the plate; whereas, if the planet
remained quite unmoved relatively to the stars it would give a dot
like the star dots. The presence of a line, therefore, at once
indicates a planet.
This method of planet-hunting has proved most useful. More than 400
small planets similar to Piazzi's have been found, though never
another one like Uranus and Neptune. As we have said, all these
little bodies lie between Mars and Jupiter. They evidently belong
to a group or family, and many astronomers have been led to believe
that they are but fragments of a former large planet.