circumstance which makes scientific research trustworthy caused the
unscientific to entertain doubt. If men of science were to arrange
beforehand with each other what observations they should publish, how
their accounts should be ended, what theories they would endeavour to
establish, their results would seem far more trustworthy, their theories
far more probable, than according to the method actually adopted.
Science, which should be exact, seems altogether inexact, because one
observer seems to obtain one result, another a different result.
Scientific theories seem unworthy of reliance because scientific men
entertain for a long time rival doctrines. But in another and a worthier
sense than as the words are used in the 'Critic,' when men of science do
agree their agreement is wonderful. It _is_ wonderful, worthy of all
admiration, because before it has been attained errors long entertained
have had to be honestly admitted; because the taunt of inconsistency is
not more pleasant to the student of science than to others, and the man
who having a long time held one doctrine adopts and enforces another
(one perhaps which he had long resisted), is sure to be accused by the
many of inconsistency, the truly scientific nature of his procedure
being only recognised by the few. The agreement of men of science ought
to be regarded also as most significant in another sense. So long as
there is room for refusing to admit an important theory advanced by a
student of science, it is natural that other students of science should
refuse to do so; for in admitting the new theory they are awarding the
palm to a rival. In strict principle, of course, this consideration
ought to have no influence whatever; as a matter of fact, however, men
of science, being always men and not necessarily strengthened by
scientific labours against the faults of humanity, the consideration has
and must always have influence. Therefore, when the fellow-writers and
rivals of Newton or of his followers gave in their adhesion to the
Newtonian theory; when in our own time--but let us leave our own time
alone, in this respect--when, speaking generally, a novel doctrine, or
some new generalisation, or some great and startling discovery, is
admitted by rival students of the branch of astronomy to which it
belongs, the probability is great that the weight of evidence has been
found altogether overwhelming.
Let us now, however, turn to cases in which, while many observations
seem to point to some result, it has appeared that, after all, those
observations must have been illusory.
A striking instance in point is found in the perplexing history of the
supposed satellite of Venus.
On January 25, 1672, the celebrated astronomer, J.D. Cassini saw a
crescent shaped and posited like Venus, but smaller, on the western side
of the planet. More than fourteen years later, he saw a crescent east of
the planet. The object continued visible in the latter case for half an
hour, when the approach of daylight obliterated the planet and this
phantom moon from view. The apparent distance of the moon from Venus was
in both cases small, viz., only one diameter of the planet in the former
case, and only three-fifths of that diameter in the latter.
Next, on October 23, 1740, old style, the optician Short, who had had
considerable experience in observation, saw a small star perfectly
defined but less luminous than Venus, at a distance from the planet
equal to about one-third of the apparent diameter of our moon. This is a
long distance, and would correspond to a distance from Venus certainly
not less than the moon's distance from the earth. Short was aware of the
risk of optical illusion in such matters, and therefore observed Venus
with a second telescope; he also used four eye-pieces of different
magnifying power. He says that Venus was very distinct, the air very
pure, insomuch that he was able to use a power of 240. The seeming moon
had a diameter less than a third of Venus's, and showed the same phase
as the planet. Its disc was exceedingly well defined. He observed it
several times during a period of about one hour.
Still more convincing, to all appearance, is the account of the
observations made by M. Montaigne, as presented to the Academy of
Sciences at Paris by M. Baudouin in 1761. The transit of Venus which was
to take place on June 6 in that year led to some inquiry as to the
satellite supposed to have been seen by Cassini and Short, for of course
a transit would be a favourable occasion for observing the satellite. M.
Montaigne, who had no faith in the existence of such an attendant, was
persuaded to look for it early in 1761. On May 3 he saw a little
crescent moon about twenty minutes of arc (nearly two-thirds the
apparent diameter of our moon) from the planet. He repeated his
observation several times that night, always seeing the small body, but
not quite certain, despite its crescent shape, whether it might not be a
small star. On the next evening, and again on May 7 and 10, he saw the
small companion apparently somewhat farther from Venus and in a
different position. He found that it could be seen when Venus was not in
the field of view. The following remarks were made respecting these
observations in a French work, 'Dictionnaire de Physique,' published in
1789:--'The year 1761 will be celebrated in astronomy in consequence of
the discovery that was made on May 3 of a satellite circulating round
Venus. We owe it to M. Montaigne, member of the Society of Limoges. M.
Baudouin read before the Academy of Sciences at Paris a very interesting
memoir, in which he gave a determination of the revolution and distance
of the satellite. From the calculations of this expert astronomer we
learn that the new star has a diameter about one-fourth that of Venus,
is distant from Venus almost as far as the moon from our earth, has a
period of nine days seven hours' [much too short, by the way, to be
true, expert though M. Baudouin is said to have been], 'and its
ascending node'--but we need not trouble ourselves about its ascending
node.
Three years later Roedkier, at Copenhagen, March 3 and 4, 1764, saw the
satellite of Venus with a refracting telescope 38 feet long, which
should have been effective if longitude has any virtue. He could not see
the satellite with another telescope which he tried. But several of his
friends saw it with the long telescope. Amongst others, Horrebow,
Professor of Astronomy, saw the satellite on March 10 and 11, after
taking several precautions to prevent optical illusion. A few days later
Montbaron, at Auxerre, who had heard nothing of these observations, saw
a satellite, and again on March 28 and 29 it appeared, always in a
different position.
It should be added that Scheuten asserted that during the transit of
1761 Venus was accompanied by a small satellite in her motion across the
sun's face.
So confidently did many believe in this satellite of Venus that
Frederick the Great, who for some reason imagined that he was entitled
to dispose as he pleased of the newly discovered body, proposed to
assign it away to the mathematician D'Alembert, who excused himself from
accepting the questionable honour in the following terms:--
'Your Majesty does me too much honour in wishing to baptize this new
planet with my name. I am neither great enough to become the satellite
of Venus in the heavens, nor well enough (_assez bien portant_) to be so
on the earth, and I am too well content with the small place I occupy in
this lower world to be ambitious of a place in the firmament.'
It is not at all easy to explain how this phantom satellite came to be
seen. Father Hell, of Vienna--the same astronomer whom Sir G. Airy
suspects of falling asleep during the progress of the transit of Venus
in 1769--made some experiments showing how a false image of the planet
might be seen beside the true one, the false image being smaller and
fainter, like the moons seen by Schort (as Hell called Short), Cassini,
and the rest. And more recently Sir David Brewster stated that Wargentin
'had in his possession a good achromatic telescope, which always showed
Venus with such a satellite.' But Hell admitted that the falsehood of
the unreal Venus was easily detected, and Brewster adds to his account
of Wargentin's phantom moon, that 'the deception was discovered by
turning the telescope about its axis.' As Admiral Smyth well remarks, to
endeavour to explain away in this manner the observations made by
Cassini and Short 'must be a mere pleasantry, for it is impossible such
accurate observers could have been deceived by so gross a neglect.'
Smyth, by the way, was a believer in the moon of Venus. 'The contested
satellite is perhaps extremely minute,' he says, 'while some parts of
its body may be less capable of reflecting light than others; and when
the splendour of its primary and our inconvenient station for watching
it are considered, it must be conceded that, however slight the hope may
be, search ought not to be relinquished.'
Setting aside Scheuten's asserted recognition of a dark body near Venus
during the transit of 1761, Venus has always appeared without any
attendant when in transit. As no one else claimed to have seen what
Scheuten saw in 1761, though the transit was observed by hundreds, of
whom many used far finer telescopes than he, we must consider that he
allowed his imagination to deceive him. During the transit of 1769, and
again on December 8-9, 1874, Venus certainly had no companion during her
transit.
What, then, was it that Cassini, Short, Montaigne, and the rest supposed
they saw? The idea has been thrown out by Mr. Webb that mirage caused
the illusion. But he appears to have overlooked the fact that though an
image of Venus formed by mirage would be fainter than the planet, it
would not be smaller. It might, according to the circumstances, be above
Venus or below, or even somewhat towards either side, and it might be
either a direct or an inverted image, but it could not possibly be a
diminished image.
Single observations like Cassini's or Short's might be explained as
subjective phenomena, but this explanation will not avail in the case of
the Copenhagen observations.
I reject, as every student of astronomy will reject, the idea of wilful
deception. Occasionally an observer may pretend to see what he has not
seen, though I believe this very seldom happens. But even if Cassini and
the rest had been notoriously untrustworthy persons instead of being
some of them distinguished for the care and accuracy with which their
observations were made and recorded, these occasional views of a phantom
satellite are by no means such observations as they would have invented.
No distinction was to be gained by observations which could not be
confirmed by astronomers possessing more powerful telescopes. Cassini,
for example, knew well that nothing but his well-earned reputation could
have saved him from suspicion or ridicule when he announced that he had
seen Venus attended by a satellite.
It seems to me probable that the false satellite was an optical illusion
brought about in a different way from those referred to by Hell and
Brewster, though among the various circumstances which in an imperfect
instrument might cause such a result I do not undertake to make a
selection. It is certain that Venus's satellite has vanished with the
improvement of telescopes, while it is equally certain that even with
the best modern instruments illusions occasionally appear which deceive
even the scientific elect. Three years have passed since I heard the
eminent observer Otto Struve, of Pulkowa, give an elaborate account of a
companion to the star Procyon, describing the apparent brightness,
distance, and motions of this companion body, for the edification of the
Astronomer-Royal and many other observers. I had visited but a few
months before the Observatory at Washington, where, with a much more
powerful telescope, that companion to Procyon had been systematically
but fruitlessly sought for, and I entertained a very strong opinion,
notwithstanding the circumstantial nature of Struve's account and his
confidence (shared in unquestioningly by the observers present), that he
had been in some way deceived. But I could not then see, nor has any one
yet explained, how this could be. The fact, however, that he had been
deceived is now undoubted. Subsequent research has shown that the
Pulkowa telescope, though a very fine instrument, possesses the
undesirable quality of making a companion orb for all first-class stars
in the position where O. Struve and his assistant Lindenau saw the
supposed companion of Procyon.
I may as well point out, however, that theories so wild have recently
been broached respecting Venus, that far more interesting explanations
of the enigma than this optical one may be looked for presently. It has
been gravely suggested by Mr. Jos. Brett, the artist, that Venus has a
surface of metallic brilliancy, with a vitreous atmosphere,--which can
only be understood to signify a glass case. This stupendous theory has
had its origin in an observation of considerable interest which
astronomers (it is perhaps hardly necessary to say) explain somewhat
differently. When Venus has made her entry in part upon the sun's face
at the beginning of transit, there is seen all round the portion of her
disc which still remains outside the sun an arc of light so brilliant
that it records its photographic trace during the instantaneous exposure
required in solar photography. It is mathematically demonstrable that
this arc of light is precisely what _should_ be seen if Venus has an
atmosphere like our earth's. But mathematical demonstration is not
sufficient (or perhaps we may say it is too much) for some minds.
Therefore, to simplify matters, Venus has been provided with a mirror
surface and a glass case. (See preceding essay, on Astronomical
Paradoxes, for further details.)
The enigma next to be considered is of a more doubtful character than
the myth relating to the satellite of Venus. Astronomers are pretty well
agreed that Venus has no moon, but many, including some deservedly
eminent, retain full belief in the story of the planet Vulcan.
More than seventeen years ago the astronomical world was startled by the
announcement that a new planet had been discovered, under circumstances
unlike any which had heretofore attended the discovery of fresh members
of the solar system. At that time astronomers had already become
accustomed to the discovery, year after year, of several asteroids,
which are in reality planets, though small ones. In fact, no less than
fifty-six of these bodies were then known, whereof fifty-one had been
discovered during the years 1847-1858 inclusive, not one of these years
having passed without the detection of an asteroid. But all these
planets belonged to one family, and as there was every reason to believe
that thousands more travel in the same region of the solar system, the
detection of a few more among the number had no longer any special
interest for astronomers. The discovery of the first known member of the
family had indeed been full of interest, and had worthily inaugurated
the present century, on the first day of which it was made. For it had
been effected in pursuance of a set scheme, and astronomers had almost
given up all hopes of success in that scheme when Piazzi announced his
detection of little Ceres. Again the discovery of the next few members
of the family had been interesting as revealing the existence of a new
order of bodies in the solar system. No one had suspected the
possibility that besides the large bodies which travel round the sun,
either singly or attended by subordinate families of moons, there might
be a ring of many planets. This was what the discovery of Ceres, Pallas,
Juno, and Vesta seemed to suggest, unless--still stranger thought--these
were but fragments of a mighty planet which had been shattered in
long-past ages by some tremendous explosion. Since then, however, this
startling theory has been (itself) exploded. Year after year new members
of the ring of multitudinous planets are discovered, and that, not as
was recently predicted, in numbers gradually decreasing, but so rapidly
that more have been discovered during the last ten years than during the
preceding twenty.
The discovery of the giant planet Uranus, an orb exceeding our earth
twelve and a half times in mass and seventy-four times in volume, was a
matter of much greater importance, so far as the dignity of the
planetary system was concerned, for it is known that the whole ring of
asteroids together does not equal one-tenth part of the earth in mass,
while Uranus exceeds many times in volume the entire family of
terrestrial planets--Mercury, Venus, the Earth, and Mars. The detection
of Uranus, unlike that of Ceres, was effected by accident. Sir W.
Herschel was looking for double stars of a particular kind in the
constellation Gemini when by good fortune the stranger was observed.
The interest with which astronomers received the announcement of the
discovery of Uranus, though great, was not to be compared with that with
which they deservedly welcomed the discovery of Neptune, a larger and
more massive planet, revolving at a distance one-half greater even than
the mighty space which separates Uranus from the sun, a space so great
that by comparison with it the range of 184,000,000 of miles, which
forms the diameter of our earth's orbit, seems quite insignificant. It
was not, however, the vastness of Neptune's mass or volume, or the awful
remoteness of the path along which he pursues his gloomy course, which
attracted the interest of astronomers, but the strangeness of the
circumstances under which the planet had been detected. His influence
had been felt for many years before astronomers thought of looking for
him, and even when the idea had occurred to one or two, it was
considered, and that, too, by an astronomer as deservedly eminent as Sir
G. Airy, too chimerical to be reasonably entertained. All the world now
knows how Leverrier, the greatest living master of physical astronomy,
and Adams, then scarce known outside Cambridge, both conceived the idea
of finding the planet, not by the simple method of looking for it with a
telescope, but by the mathematical analysis of the planet's disturbing
influence upon known members of the solar system. All know, too, that
these mathematicians succeeded in their calculations, and that the
planet was found in the very region and close to the very point
indicated first by Adams, and later, but independently, and (fortunately
for him more publicly) by Leverrier.
None of these instances of the discovery of members of the solar system
resembled in method or details the discovery announced early in the year
1859. It was not amid the star-depths and in the darkness of night that
the new planet was looked for, but in broad day, and on the face of the
sun himself. It was not on the outskirts of the solar system that the
planet was supposed to be travelling, but within the orbit of Mercury,
hitherto regarded as of all planets the nearest to the sun. It was not
hoped that any calculation of the perturbations of other planets would
show the place of the stranger, though certain changes in the orbit of
Mercury seemed clearly enough to indicate the stranger's existence.
Early in 1860 Leverrier had announced that the position of Mercury's
path was not precisely in agreement with calculations based on the
adopted estimates of the masses of those planets which chiefly disturb
the motions of Mercury. The part of the path where Mercury is nearest to
the sun, and where, therefore, he travels fastest, had slightly shifted
from its calculated place. This part of the path was expected to move,
but it had moved more than was expected; and of course Mercury having
his region of swiftest motion somewhat differently placed than was
anticipated, himself moved somewhat differently.
Leverrier found that to explain this feature of Mercury's motion either
the mass of Venus must be regarded as one-tenth greater than had been
supposed, or some unknown cause must be regarded as affecting the motion
of Mercury. A planet as large as Mercury, about midway between Mercury
and the sun, would account for the observed disturbance; but Leverrier
rejected the belief that such a planet exists, simply because he could
not 'believe that it would be invisible during total eclipses of the
sun.' 'All difficulties disappear,' he added, 'if we admit, in place of
a single planet, small bodies circulating between Mercury and the sun.'
Considering their existence as not at all improbable, he advised
astronomers to watch for them.
It was on January 2, 1860, that Leverrier thus wrote. On December 22,
1859, a letter had been addressed by a M. Lescarbault of Orgeres to
Leverrier, through M. Vallee, hon. inspector-general of roads and
bridges, announcing that on March 26, 1859, about four in the afternoon,
Lescarbault had seen a round black spot on the face of the sun, and had
watched it as it passed across like a planet in transit--not with the
slow motion of an ordinary sun-spot. The actual time during which the
round spot was visible was one hour, seventeen minutes, nine seconds,
the rate of motion being such that, had the spot crossed the middle of
the sun's disc, at the same rate, the transit would have lasted more
than four hours. The spot thus merely skirted the sun's disc, being at
no time more than about one forty-sixth part of the sun's apparent
diameter from the edge of the sun. Lescarbault expressed his conviction
that on a future day, a black spot, perfectly round and very small, will
be seen passing over the sun, and 'this point will very probably be the
planet whose path I observed on March 26, 1859.' 'I am persuaded,' he
added, 'that this body is the planet, or one of the planets, whose
existence in the vicinity of the sun M. Leverrier had made known a few
months ago' (referring to the preliminary announcement of results which
Leverrier published afterwards more definitely).
Leverrier, when the news of Lescarbault's observation first reached him,
was surprised that the observation should not have been announced
earlier. He did not consider the delay sufficiently justified by
Lescarbault's statement that he wished to see the spot again. He
therefore set out for Orgeres, accompanied by M. Vallee. 'The
predominant feeling in Leverrier's mind,' says Abbe Moigno, 'was the
wish to unmask an attempt to impose upon him, as the person more likely
than any other astronomer to listen to the allegation that his prophecy
had been fulfilled.'
'One should have seen M. Lescarbault,' says Moigno, 'so small, so
simple, so modest, and so timid, in order to understand the emotion with
which he was seized, when Leverrier, from his great height, and with
that blunt intonation which he can command, thus addressed him: "It is
then you, sir, who pretend to have observed the intra-mercurial planet,
and who have committed the grave offence of keeping your observation
secret for nine months. I warn you that I have come here with the
intention of doing justice to your pretensions, and of demonstrating
either that you have been dishonest or deceived. Tell me, then,
unequivocally, what you have seen."' This singular address did not bring
the interview, as one might have expected, to an abrupt end. The lamb,
as the Abbe calls the doctor, trembling, stammered out an account of
what he had seen. He explained how he had timed the passage of the black
spot. 'Where is your chronometer?' asked Leverrier. 'It is this watch,
the faithful companion of my professional journeys.' 'What! with that
old watch, showing only minutes, dare you talk of estimating seconds. My
suspicions are already too well confirmed.' 'Pardon me, I have a
pendulum which beats seconds.' 'Show it me.' The doctor brings down a
silk thread to which an ivory ball is attached. Fixing the upper end to
a nail, he draws the ball a little from the vertical, counts the number
of oscillations, and shows that his pendulum beats seconds; he explains
also how his profession, requiring him to feel pulses and count
pulsations, he has no difficulty in mentally keeping record of
successive seconds.