In our articles on the Revelations of Astronomy, and on the Discovery of the Planet Neptune, we submitted to our readers a popular account of the bodies of the solar and sidereal systems, and of the comets, or wandering stars, which occasionally cross them in their path. Since that time important discoveries have been made in the science, by the use of fine telescopes, and improved methods of observation; and speculation, which has hitherto performed but a small part in accelerating the march of astronomy, has begun to assert its just influence, not only in predicting the existence of new planets, but in exploring the inner life of the planetary system.

Within a few years, new satellites have been found circulating round some of the remoter planets, while the structure and condition of the planets themselves have been studied with the improved telescopes now in the hands of astronomers. No fewer than fifty-eight new planets, or asteroids, as they have been called from their smallness, have been discovered between Mars and Jupiter; and, what is more interesting still, M. Leverrier, one of the discoverers of Neptune, had, from theoretical considerations, suggested by irregularities in the motions of Mercury, predicted the existence of a planet, or a ring of planets, between that body and the Sun; and M. Lescarbault has actually discovered this intra-mercurial planet, while it was passing in the form of a round black spot over the disc of the Sun.

The history of this discovery, if it is a discovery, is one of the most curious chapters in the annals of science. It has been characterized as "the Romance of the New Planet;" and astronomers of no mean celebrity are now marshalled in hostile array in discussing the question of its existence.

On the 2d January 1860, M. Leverrier communicated to the Academy of Sciences a remarkable paper on the Theory of Mercury. In studying the 21 transits of that body over the Sun between 1697 and 1848, he found that the observations could not be represented by the received elements of the planet, but that they could be all represented, nearly to a second, by augmenting by 38 seconds the secular motion of the perihelion of Mercury. In order to justify such an increase, we must increase the mass attributed to Venus one-tenth at least of its value, which, from sixty years meridian observations, has been found to be the four hundred thousandth part of that of the Sun. If we admit this increased mass of Venus, we must conclude, either that the secular variation of the obliquity of the Ecliptic, deduced from observations, is affected with errors by no means probable, or that the obliquity is changed by other causes wholly unknown to us. If, on the other hand, we regard the variation of the obliquity of the Ecliptic, and the causes which produce it, as well established, we must believe that the excess of motion in the perihelion of Mercury is due to some unknown action. 

"I do not intend," says M. Leverrier, "to decide absolutely between these two hypotheses. I wish only to draw the attention of astronomers to a grave difficulty, and to make it the subject of a serious discussion." We must therefore, as he suggests, find a cause which shall impress upon the perihelion of Mercury these 38 seconds of secular motion, without producing any other sensible effect upon the planetary system .

M. Leverrier then shows that a planet between Mercury and the Sun, the size of Mercury, situated at half his mean distance from the Sun, if moving in a circular orbit slightly inclined to that of Mercury, would produce the 38 seconds of secular motion in his perihelion. But when he considers that such a planet would have certainly a very great brightness, he cannot think that it would be invisible at its greatest elongation, or during total eclipses of the Sun.

"All these difficulties," he adds, "disappear, if we admit, in place of a single planet, small bodies circulating between Mercury and the Sun;" and he thinks their existence not at all improbable, seeing that we have already a ring of 58 such bodies between Mars and Jupiter. As these bodies must frequently pass over the Sun's disc, he advises astronomers to search for them with care.

With the view of discovering these bodies, M. Faye, the distinguished colleague of M. Leverrier, has submitted the following plan of operation. Considering that the brightness of the region round the Sun will not permit us to see such small planets as those indicated by M. Leverrier, he proposes that observations should be made during the darkness of solar eclipses, and particularly during that of July next. Instead of following the Sun to the last moment of total darkness, he suggests that the observer should keep in the dark for a quarter of an hour, in order that his eye should be more sensitive at the decisive moment, in order to perceive the smallest speck of light that may radiate from the neighbourhood of the Sun. We would add to the suggestion, that if he fancies he sees such a luminous speck, he should look away from it, in order to throw its image on a more sensitive part of the retina, -a process which has enabled astronomers to see a satellite of Saturn, invisible when looked at directly. In such a search, it is not less important that the pupil should, if necessary, be expanded by belladonna or hyoscyamus, in order to embrace the whole pencil of rays which fall upon the object-glass of his telescope.

M. Faye proposes also, as suggested by Sir J. Herschel, that in several observatories, suitably chosen, the Sun should be photographed several times a-day, by the help of a large instrument. “I have myself,” he says, "shown how to give to these photographs the value of an astronomical observation, by taking two impressions on the same plate after an interval of two minutes It will be sufficient to superpose the transparent negatives of this size, taken at a quarter of an hour's interval, to distinguish immediately the moveable projection of an asteroid in the middle of the most complex groups of small spots."

While these two distinguished astronomers were occupied with this inquiry, and inventing methods of discovering the disturber of Mercury, they were little aware that a humble individual had cut the knot which they proposed to untie.

During the last century, various continental astronomers had observed, among the spots that so frequently appear on the Sun's surface, one more round than the rest, and had fortunately recorded the fact, and the date of its appearance. They do not seem, however, to have suspected that it might be a planet, and therefore did not attempt to trace it across the Sun's disc, or to watch for its reappearance. The phenomenon was at last seen by a more sagacious observer, who was able to appreciate its importance, and anxious to trace it to its cause. This observer was M. Lescarbault, a doctor of medicine of the Faculty of Paris, and carrying on his profession at Orgeres, a small town in the arrondissement of Chateaudun, in the department of the Eure and the Loire. Having been fond of astronomy from his infancy, and having since 1837 observed that the law of Bode was far from representing accurately the distances of the planets from the Sun, he imagined that, independently of the four small planets, Ceres, Pallas, Juno, and Vesta, which Piazzi, Olbers, and Harding had, between 1801 and 1807, discovered in the wide space between Mars and Jupiter, there might be another elsewhere. But as he was then situated, he found it difficult to make the necessary observations.

When he was watching the transit of Mercury over the Sun, on the 8th May 1845, the idea occurred to him, that if there was any other planet between the Sun and the Earth than Venus and Mercury, it ought to be seen in its passages across the disc of that luminary; and that, by frequently observing the margin of the Sun's disc, we ought to see the appearance of a black spot entering upon the Sun, and traversing his disc, in a line of a greater or less length.

At this time it was impossible for him to institute this plan of observation, and it was not till 1853 that he was able to commence it. Between 1853 and 1858, he seldom directed his telescope to the sun; but in 1858, when he had a terrace at his command, he constructed a rude instrument, by which he could measure, within a degree nearly, the angle of position; and he tested its accuracy by measuring the position of spots on the Moon, and comparing his observations with a map of that satellite published by John Dominique Cassini.

This instrument was a telescope, with an object-glass about four inches in aperture, and four feet ten inches in focal length, made in 1838 by M. Cauche, and having a magnifying power of 150 times. The finder of the telescope magnified six times. In the focus of both telescopes were placed three parallel vertical wires, and three parallel horizontal ones, the distance between the two outermost being from 32 to 34 minutes. A circle of card-board, 5½ inches in diameter, and divided in its circumference to half degrees, was placed on the eye-piece of the finder, and concentric with it. The telescope had a vertical and horizontal motion, and was supported by a wooden pillar with three feet, the points of which rested on a frame also with three feet, and having screws, in order to level the instrument.

With his telescope thus mounted, and by the aid of other pieces of rude apparatus, which it is unnecessary to describe, he was able to measure the distance of any well-defined spot on the Sun's disc from its margin.

Whenever our observer expected that the duties of his profession would allow him a little leisure for observation after mid-day, he regulated his watch by the Sun's passing the meridian, by means of a small transit instrument; and having adjusted the rest of his apparatus, he directed his telescope to the Sun, and, during a period varying from half an hour to three hours, he surveyed the whole contour of the Sun's disc, keeping his eye at the eye-glass.

After these repeated surveys of the great luminary, he was at last gratified with the object of his ambition. On the 26th March 1859, about four o'clock in the afternoon, he saw a black point enter the Sun's disc. Its circumference was well defined. Its angular diameter, as seen from the Earth, was very small; and he estimated it as much less than one-fourth of that of Mercury, which he had seen with the same telescope and the same magni-fying power when it passed over the Sun on the 8th May 1845.

[...]

The letter of which we have given the substance was dated the 22d December 1859, and was brought to M. Leverrier by M. Vallée, Honorary Inspector-General of Roads and Bridges; and he was led, from the details which it contained, to place in them a certain degree of confidence. He was surprised, however, that M. Lescarbault, when he had made such a remarkable discovery, should have allowed nine months to elapse without communicating it. This delay, which was not sufficiently justified by the statement that he wished to see the black spot again before he made his discovery public, induced M. Leverrier to set out immediately for Orgeres, to which he was accompanied by M. Vallée, Junior Engineer of Roads and Bridges.

On their arrival at Orgeres, without any previous notice, they found in M. Lescarbault a man who had been long devoted to scientific pursuits, surrounded with instruments and apparatus of every kind constructed by himself, and provided even with a small revolving cupola. He permitted his visitors to examine in the most careful manner the instruments which he used, and he gave them the most minute explanations regarding his works, and especially regarding all the circumstances of the transit of the planet over the Sun.

The entry of the planet on the Sun's disc was not observed by him, as might be inferred from his letter. It had, before he saw it, described a line of some seconds on the Sun's face, and it was only from an estimate of its velocity that he deduced the time of its entry. The angles of position relative to a vertical line were measured in the way he has described in his letter; and it was by transferring these observations to a celestial sphere that he was able to determine the length of the chord described by the planet, and to ascertain the time that it would take to traverse the whole disc of the Sun.

The explanations of M. Lescarbault, and the simplicity with which they were given, inspired M. Leverrier and his friend with the most perfect conviction that the observations deserve to be admitted into science, and that the long delay in publishing them arose only from a modest and calm reserve, which may be expected at a distance from the agitation of towns. It was an article in Cosmos, on M. Leverrier's theory of the perturbation of Mercury, that induced M. Lescarbault to break the silence which he had so long preserved.

In submitting to calculation the data supplied by observation, M. Leverrier has found that the chord described by the planet over the Sun's disc is 9'17", and the time of traversing the whole disc 4h. 26m. 48s., --- numbers which differ very little from those of Lescarbault, and proving that he had taken great pains in the graphical deductions from his observations, and that the observations themselves possessed a certain accuracy in spite of the imperfect means by which they were obtained.

The time of the planet's transit will give us its distance from the Sun only on the hypothesis of a circular orbit. On this hypothesis, half the major axis of the orbit will be 0.147, that of the Earth being unity. Hence the time of its revolution will be 19 days 17 hours.

[...]

According to M. Lescarbault's observation of Mercury when passing over the Sun in 1845, the diameter of that planet was certainly quadruple of the apparent diameter of the planet observed on the 26th March 1859. Considering the masses as proportional to the volumes, M. Leverrier concludes that the mass of this last planet is only the seventeenth part of the mass of Mercury, a mass too small, at the distance at which it is placed, to produce the whole of the anomaly which he had found in the motion of the perihelion of Mercury.

The new planet, in consequence of the small radius of its orbit, will never have a greater elongation, or distance from the Sun, than 8 °; and as the whole light which it sends to us is, according to Leverrier, more feeble than that of Mercury, we may readily understand why it had not hitherto been seen.

Such is the account M. Leverrier gave, at the public meeting of the Academy of Sciences on the 2d of January last, of his visit to Orgeres, and of the conclusions which he has drawn from M. Lescarbault's observations. It excited, as might have been expected, the liveliest interest in Paris. Exaggerated in its details, and embellished every time it was told, the scientific melodrame of Orgeres was the only topic of converse at the seances of philosophy and in the salons of fashion. Garibaldi and the weather ceased to interest the Parisians; and the village doctor, in his extempore observatory, and his round black spot, appropriately bearing the name of VULCAN, were the only subjects of discussion, and the only objects of learned and unlearned admiration.

Leverrier was of course the lion in every gay salon, and was obliged to recount the story of his journey to Orgeres in its dramatic phase, and without the reserve which was required in his communication to the Institute. On one of these occasions, when he was detailing the motives, the incidents, and the results of his visit to Lescarbault to a brilliant party at the house of his father-in-law, M. Choquet, he was fortunate enough to have among his audience the celebrated savant M. L'Abbé Moigno, who has reproduced in his Cosmos¹ the fascinating history, as it fell from the lips of the greatest astronomer of the age.

For a long time M. Leverrier refused to attach any credit to the reports which reached him on the subject. He could not believe that the discovery of a new planet could have been kept secret for nine months, and that a humble village doctor could have been the person to discover it. As the Director of the Imperial Observatory, however, it was his duty to inquire into the truth of the report; and having a personal interest in the question as the predictor of a planet near the Sun, he resolved to enter upon the investigation. Lescarbault's letter to himself, of the 22d December, confirmed him in this resolution; and though he had a secret conviction that the story might be true, yet the predominant feeling in his mind was 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.

He accordingly set out from Paris by railway, on Friday the 30th December, accompanied by M. Vallée as a witness of the stern inquisition which he was about to institute. Orgeres was unfortunately twelve miles distant from the nearest station, and our travellers were obliged to perform the journey on foot. On their arrival at the house of M. Lescarbault, M. Leverrier knocked loudly at the door; and when the Doctor himself had opened it, his visitor declined to give his name and his titles.

"One should have seen M. Lescarbault," says Abbé 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.' The lamb, as the Abbé calls the Doctor, trembled at this rude summons from the lion, and, unable to speak, he stammered out the following reply: 'On the 26th March, about four o'clock, I directed my telescope to the Sun, as I had been in the habit of doing, when, to my surprise, I observed, at a small distance from its margin, a black spot well defined and perfectly round, and advancing with a very sensible motion upon the disc of the Sun. Unfortunately, however, a customer arrived. I came down from the observatory, and in this painful situation I replied as I best could to the inquiries which were made, and returned to the observatory. The round spot had continued its transit; and I saw it disappear at the opposite margin of the Sun, after having been projected upon his dise for nearly an hour and a half.' 'You will then have determined,' asks Leverrier, 'the time of the first and last contact; and are you aware that the observation of the first contact is one of such extreme delicacy that professional astronomers often fail in observing it?' 'Pardon me, sir,' replies the Doctor, 'I do not pretend to have seized the precise moment of contact. The round spot was upon the disc when I first perceived it. I measured carefully its distance from the margin, and, expecting that it would describe an equal distance, I counted the time which it took to describe this second distance, and I thus determined approximately the instant of its entry.' 'To count the time is easy to say, but where is your chronometer?' 'My chronometer is a watch with minutes, 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 founded.' 'Pardon me,' was the reply, 'I have also a pendulum which nearly beats seconds.' 'Show me this pendulum,' says Leverrier. The Doctor goes up stairs, and brings down a silk thread, to which an ivory ball was suspended. 'I am anxious to see how skilfully you can thus reckon seconds.' The lamb acquiesces. He fixes the upper end of the thread to a nail, and after the ivory ball has come to rest, he draws it a little from the vertical, and counts the number of oscillations corresponding with a minute on his watch, and thus proves that his pendulum beats seconds. This is not enough,' replies the lion; it is one thing that your pendulum beats seconds, but it is another that you have the sentiment of the second beaten by your pendulum in order that you may count the seconds in observing. 'Shall I venture to tell you, says the lamb, that my profession is to feel pulses and count their pulsations? My pendulum puts the second in my ears, and I have no difficulty in counting several successive seconds. '

"'This is all very well for the chapter of time,' says the Director; 'but in order to see so delicate a spot, you require a good telescope. Have you one?" "Yes, sir, I have succeeded, not without difficulty, privation, and suffering, to obtain for myself a telescope. After practising much economy, I purchased from M. Cauche, an artist little known, though very clever, an object-glass nearly four inches in diameter. Knowing my enthusiasm and my poverty, he gave me the choice among several excellent ones; and as soon as I made the selection, I mounted it on a stand with all its parts; and I have recently indulged myself with a revolving platform, and a revolving roof, which will soon be in action. 'The lion went to the upper story, and satisfied himself of the accuracy of the statement. This is all well,' says he, 'in so far as the observation itself is concerned; but I want to see the original memorandum which you made of it.'

"'It is very easy,' answered the Doctor,' to say you want it; but though this note was written on a small square of paper, which I generally throw away or burn when it is of no further use, yet it is possible I may still find it.' Running with fear to his Connaissance des Temps, he finds the note of the 26th March 1859 performing the part of a marker, and covered with grease and laudanum. The lion seizes it greedily, and, comparing it with the letter which M. Vallée had brought him, he exclaims: 'But, sir, you have falsified this observation; the time of emergence is four minutes too late.' 'It is,' replied the lamb. Have the goodness to examine it more narrowly, and you will find that the four minutes is the error of my watch, regulated by sidereal time.' 'This is true; but how do you regulate your watch by sidereal time?' 'I have a small telescope---here it is which you will find in such a state as to enable me to obtain the time to a second, or even to some fractions of a second."

Satisfied on this point, Leverrier then wished to know how he determined the two angular co-ordinates of the points of contact, of the entry and emergence of the planet, and how he measured the chord of the arc which separates these two points. Lescarbault told him that this was reduced to the measuring the distances of these points from the vertical, and the angles of position, which he did by the systems of parallel axes we have mentioned, and the divided circle of card-board placed upon his finder.

Leverrier next inquired if he had made any attempt to deduce the planet's distance from the Sun from the period of four hours which it required to describe an entire diameter of the Sun. The Doctor confessed that he had many attempts to do this, but, not being a mathematician, he had not succeeded; and that this failure was the reason why he had delayed the announcement of his discovery. Leverrier having asked for the rough draught of these calculations, the Doctor replied, "My rough draughts! Paper is rather scarce with us. I am a joiner as well as an astronomer. I calculate in my workshop, and I write upon the boards; and when I wish to use them in new calculations, I remove the old ones by planing." On visiting, however, the carpenter's shop, they found the board, with its lines and its numbers in chalk still unobliterated.

When this cross-questioning, which had lasted an hour, was finished, Leverrier was convinced that an intra-mercurial planet had really been seen, and, with a grace and dignity full of kindness, he congratulated Lescarbault on the important discovery which he had made. Anxious to obtain some mark of respect for the discoverer of Vulcan, Leverrier made inquiry concerning his private character, and learned from the village curé, the juge de paix, and other functionaries, that he was a skilful physician, and a worthy man. With such high recommendations, M. Leverrier requested from M. Rouland, the Minister of Public Instruction, the decoration of the Legion of Honour for M. Lescarbault. The minister, in a brief but interesting statement of his claim, communicated this request to the Emperor, who, by a decree dated January 25th, conferred upon the village astronomer the honour so justly due to him. His professional brethren in Paris were equally solicitous to testify their regard; and MM. Felix Roubaud, Legrande, and Caffe, as delegates of the scientific press, proposed to the medical body, and to the scientific world in Paris, to invite Lescarbault to a banquet in the Hotel de Louvre, on the 18th of January.¹ A similar offer had been made to him by his professional admirers in Chartres and Blois; but he declined all these invitations, pleading as an excuse his simple and retired habits, and the difficulty of leaving the patients under his care.

The interesting documents which we have attempted to analyze and abridge, excited the greatest sensation in every part of Europe; and the records of astronomical observations were diligently searched, in order to find if any round black spots had been seen on the disc of the Sun. Astronomers, too, of all ranks, whether occupying well-furnished observatories, or supplied only with a telescope and a darkening glass, have been watching the little planet during the time when it was likely to pass over the Sun. No rediscovery of it, however, has yet been made; but very interesting cases have been found in which a round black spot has been seen upon the Sun. 

[...]


Upon the supposition that the black spots seen upon the Sun by the astronomers above-mentioned are bodies between Mercury and the Sun, M. Wolff is of opinion that the observations can only be reconciled by the admission of at least three intra-mercurial planets.

In the number of Cosmos of the 10th February 1860, M. Radeau, of the University of Königsberg, has submitted to calculation the observations of the French physician, and he finds, upon the supposition of a circular orbit, that the mean distance of the planet from the Sun will be 0.143, and its period of revolution 19-7 days. But as we are not authorized to adopt à circular orbit, he assumes 0.25 as the superior limit of the distances of Vulcan, and finds that the aphelion distance ought still to be less than 0-25; and in making it vary from 0-206 to 0-25, he concludes that the eccentricity ought to exceed a limit which varies from 0 to 0-176, and that the superior limit of the mean distance of the planet will vary from 0.206 to 0.221. The mean distance, therefore, will always be less than 0.221, and the period of revolution less than 38 days.

These results he endeavours to confirm by the aid of the two German observations, of the 10th October 1802, and the 19th October 1819. M. Wolff combines them with the observation of the 18th January 1798; but M. Radeau objects to this, as the angular distance between January 18th and October 10th being only 100 degrees, he must, on the hypothesis of a period of 38.5 days, give the orbit an inclination of less than 1° 5', in order to explain two transits taking place at distances of at least 40° from the nodes, and less than 2° 5' even for a period of 20 days; whereas the inclination of the orbit of Vulcan is certainly between 11° and 12° 2'. The planet, or rather the black spot of 1798, cannot have been Vulcan, if we wish to identify with it the planet of 1802 and 1819.

Our limits will not permit us to follow M. Radeau in his other calculations, from which he calculates that it will be possible, in China, to see Vulcan upon the Sun's disc on the 4th of April, at 2 o'clock in the morning; and that transits continuing about 4 hours, would be visible at Paris on the 29th March about noon, on the 2d April between noon and 5 o'clock, and on the 7th April between 10 A.M. and 3 P.M., continuing 4 hours. None of these transits, however, have been seen.

[...]

M. Wolff concludes from the above numbers that these five transits may be explained by a planet whose synodical revolution is 21 days, and sidereal revolution 19-9 days; and he adds, that the factors, 82, 296, 6, and 680, being even numbers, would entitle us to adopt a synodical revolution of 42 days---a result which the observations of M. Lescarbault do not authorize.

The history of astronomy presents us with few instances in which her observations have proved false, or her observers faithless. The telescopes of one age have corrected, doubtless, the imperfect forms of sidereal groups and planetary bodies as observed in another, and the astronomical tables of the present day have thrown into the shade the calculations and predictions of earlier times; but we have no instance in which the discovery of a primary planet, or even of a satellite, has been long the subject of doubt or of controversy. Such a case has now occurred, and one which may long remain a source of disquiet, personal, if not national, in our planetary annals .

When the astronomers of the Old and the New World, and especially our distinguished friends beyond the Channel, were rejoicing in the discovery of a planet in the very presence of the Sun---a discovery predicted by one French astronomer and confirmed by another, and one likely to suggest some new phase in the condition of planetary life, when this excitement was at its height, the fortunate astronomer decorated with the Legion of Honour, and the salons of fashion instinct with scientific life, an eminent astronomer, and that astronomer a Frenchman, has presented himself boldly in the face of Europe, not only to question the existence of such a body, but to charge its discoverer with dishonesty, and impugn the very theoretical principles on which one of the greatest astronomers of the age had foretold its discovery. 

M. Liais, a French astronomer in the service of the Brazilian Government, and himself the discoverer of a comet on the 26th February last, has just published in a Danish journal a severe criticism of the letter of M. Lescarbault and the calculations of Leverrier. This paper, entitled Sur la Nouvelle Planete annoncée par M. Lescarbault, is divided into four heads, as follows:---

1. The observation of Dr Lescarbault is false.

2. Contrary to the assertion of M. Leverrier, every planet nearer the Sun than Mercury will be more visible, with telescopes, in the vicinity of the Sun than he is.

3. That in eclipses of the Sun the planet of Lescarbault has not been seen.

4. M. Leverrier's hypothesis, that there is a powerful disturbing cause between Mercury and the Sun, is founded on the supposition that astronomical observations have a precision of which they are not susceptible.

In support of the first of these bold assertions, our author states that, at the very time when the French astronomer was looking at the black spot on the Sun's face, he, M. Liais, was examining the Sun with a telescope of twice the magnifying power, and did not perceive it. This observation was made in the bay of Rio de Janeiro, at St Domingos, when M. Liais was carefully determining the decrease in the luminosity of the Sun from its centre to its circumference, and from its equator to its poles. The first of these observations was made between 11h. 4m. and 11h. 20m., and from the interruption of clouds the second was made between 12h. 42m. and 1h. 17m., on the very part of the Sun where M. Lescarbault saw the planet enter, and at a time when it must have been during a period of 12 minutes on the Sun's disc, and 1.4 from its margin. "This quantity," says M. Liais, "is too great to be accounted for by the difference of the parallaxes of Orgeres and St Domingos; and consequently, when I made my last comparison, I ought to have seen upon the Sun the black spot in question if it had been seen at Orgeres. "It is certainly not easy to conceive how M. Liais could have missed seeing the black spot, when he was using a fine telescope, and making such a nice observation on the light of the Sun's disc at the very place where the planet should have been; and had he continued his observations even for a few minutes longer, we should have admitted the force of his argument; but twelve minutes is so short a time, that it is just possible that the planet may not have entered upon the Sun during the time that he observed it. Still, however, he is entitled to assert, as he does, "that he is in a condition to deny, in the most positive manner, the passage of a planet over the Sun at the time indicated."

M. Liais proceeds to support his astronomical fact by a moral argument, which, we think, has not much force. He says, what is true, that Lescarbault contradicts himself in having first asserted that he saw the planet enter upon the Sun's disc, and having afterwards admitted to Leverrier that it had been on the disc some seconds before he saw it, and that he had merely inferred the time of its entry from the rate of its motion afterwards .

The difference of longitude of Orgeres is assumed to be 3h; but if this is not correct, the conclusions of our author are untenable. 

"If this one assertion then," says M. Liais, "be fabricated, the whole may be so;" a conclusion which we cannot accept. These arguments M. Liais considers to be strengthened by the assertion, which, as we have seen, perplexed Leverrier himself, that if M. Lescarbault had actually seen a planet on the Sun, he could not have kept it secret for nine months .

The assertion of our author, in opposition to that of Leverrier, that the planet, if one existed, ought to be seen in the vicinity of the Sun, is not so easily answered .

In support of this opinion, he enters into an elaborate calculation of the brightness of the planet Vulcan compared with that of Mercury. He asserts that, from its proximity to the Sun, it must be 74 times brighter than Mercury. But Mercury has been seen by himself and others within 7° or 8° of the Sun, and therefore, assuming the diameter of Vulcan to be 2"5 ( for which he assigns good reasons from Lescarbault's observations ), the total light which it sends to the Earth will be nearly double that of Mercury; and consequently Vulcan, Leverrier's Ring of planets, ought to have been frequently seen by astronomers in the vicinity of the Sun, when they were searching for planets and comets in that locality .

The assertion, that the planet of Lescarbault has not been seen during eclipses of the Sun, is of course true .

As the planet Mercury has been frequently observed during solar eclipses, we might reasonably expect to have seen Vulcan; and during the many observations which will be made in the vicinity of the Sun during the time of the total eclipse in July next, and doubtless both before and after it, with this object in view, Vulcan may possibly be seen .

Taking, then, into consideration the numerous observations that have been made on the Sun and in its vicinity by so many astronomers, and with such fine telescopes, M. Liais concludes, "That if the motion of the perihelion of Mercury is due to the attraction of matter lying between the Sun and this planet, this matter does not form planets, properly so called, but must be in the state of cosmical dust, and form a part of the solar nebulosity or zodiacal light."

M. Liais's last observation, questioning the existence of a disturbing force requiring for its cause the existence of a planet or planets, merits, doubtless, the attention of astronomers .

The motion of the perihelion of Mercury has been deduced from twelve observed passages of this planet. Admitting the time of the planet's entrance upon the Sun's disc to be affected with refraction, M. Liais has obtained by calculation a motion of the perihelion so much less than that assumed by Leverrier, that he can account for it by supposing the mass of Venus to be from the 10th to the 15th part greater than it is supposed to be. By admitting a possible error in the obliquity of the Ecliptic of 24 ", and consequently an increase of one-tenth in the mass of Venus, M. Liais asserts that the whole motion in the perihelion of Mercury may be explained; and he further asserts, that by abandoning the invariability of the mean motions, which supposes a constancy in the masses of which there is no proof, the position of Mercury may be explained without supposing so great a motion in his perihelion as has been alleged .

To this remarkable paper no reply has yet been made by Leverrier, or any French astronomer. In the Cosmos, however, of the 4th May, we find a letter of the Abbé Moigno prefixed to a reply to M. Liais, by M. Radeau, of Koenigsberg. The Abbé is justly offended at the expression of M. Liais, "that the observation of M. Lescarbault ( in reference to his not having seen the entry of the spot ) is partially fabricated ( apres le coup ), on after consideration." He considers it as dispensing him from refuting it; and he adds, that in order to leave no doubt in the matter, he cheerfully accepts the short reply of M. Radeau.

Although we have great confidence in the honesty of M. Lescarbault, and anxiously hope that he has made a great discovery, we cannot admit that Professor Radeau has, on any essential point, refuted either the assertions or the arguments of Liais. In the first place, he states, on the authority of the Connaissance des Temps, that the difference of longitude between Orgeres and San Domingos is 3h 2m, in place of 3h, as adopted by Liais; but, as he allows that the difference of parallaxes would have retarded the entry of the planet only about half a minute at San Domingos, he admits the great fact, that the planet ought to have appeared on the Sun's disc during the eleven minutes that M. Liais was surveying it. He then asks if M. Liais may not have made the interval of his observations---namely, 12h 42m to 1h 17m.---too wide, so as to permit us to reduce these fatal eleven or twelve minutes, as he calls them, and keep the planet so much nearer the margin of the disc as to escape the notice of Liais, whose observation he considers as simply a negative one that proves little. To this M. Liais will doubtless reply, that the limit of 1h 17mwas the limit recorded in two notes, and must therefore be held as correct.

[...]

Since the first notice of the discovery of Vulcan, in the beginning of January 1860, the Sun has been anxiously observed by astronomers; and the limited area round him in which the planet must be, if he is not upon the Sun, has doubtless been explored with equal care by telescopes of high power, and processes by which the Sun's direct light has been excluded from the tube of the telescope as well as the eye of the observer; and yet no planet has been found. This fact would entitle us to conclude that no such planet exists, if its existence had been merely conjectured, or if it had been deduced from any of the laws of planetary distance, or even if Leverrier or Adams had announced it as the probable result of planetary perturbations. If the finest telescopes cannot rediscover a planet that has a visible disc, with a power of 300, as used by Liais, within so limited an area as a circle of 16 degrees, of which the Sun is the centre, or rather within a narrow belt of that circle, we should unhesitatingly declare that no such planet exists; but the question assumes a very different aspect when it involves moral considerations. If, after the severe scrutiny which the Sun and its vicinity will undergo before, and after, and during his total eclipse in July, no planet shall be seen; and if no round black spot, distinctly separable from the usual solar spots, shall not be seen on the solar spots, we will not dare to assert that it does not exist. We cannot doubt the honesty of M. Lescarbault; and we can hardly believe that he was mistaken. No solar spot, no floating scoria, could maintain, in its passage over the Sun, a circular and uniform shape; and we are confident that no other hypothesis but that of an intra-mercurial planet can explain the phenomena seen and measured by M. Lescarbault---a man of high character, possessing excellent instruments, and in every way competent to use them well, and to describe clearly and correctly the results of his observations. Time, however, tries facts as well as speculations. The phenomenon observed by the French astronomer may never be again seen, and the disturbance of Mercury which rendered it probable, may be otherwise explained. Should this be the case, we must refer the round spot on the Sun to some of those illusions of the eve or of the brain, which have sometimes disturbed the tranquillity of science.