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Le Perrier's inrestigation of the orbit of Mercury.- Narratire of the Discovery of

Vulcan.-Le Verrier's interview with M. Lescarbaull.--Approximate elements of Vulcan.-Concluding note by Le Verrier.- Obserrations by Lummis at Manchester.-Instances of Bodies seen traversing the Sun.-Hind's opinion.- Alleged Intra-Mercurial planets discorered in America by Watson and Swift on July 29, 1878.

REFORE entering upon the story of the supposed discovery of

a new planet to which this name has been given, a brief prefatory statement seems necessary.

M. Le Verrier, having conducted an investigation into the theory of the orbit of Mercury, was led to the conclusion that a certain error in the assumed motion of the perihelion could only be accounted for by supposing the mass of Venus to be at least is greater than was commonly imagined, or else that there existed some unknown planet or planets, situated between Mercury and the Sun, capable of producing a disturbing action. In laying his views before the scientific world in the autumn of 1859, Le Verrier suggested the latter theory as a probable solution of the difficulty b.

On these views being made public, a certain M. Lescarbault, a physician at Orgères, in the Department of Eure-et-Loire, France, came forward and stated that on March 26 in that year (1859), he had observed the passage of an object across the Sun's

Compt. Rend., vol. xlix. p. 379. in detail by Newcomb in Astron. Papers 1859.

for use of Amer. Naut. Almanack, vol. i. Objections to this theory are stated p. 474. Washington, 1882.

disc which he thought might be a new planet, but which he did not like to announce as such until he had obtained a confirmatory observation; he related in writing the details of his observation, and Le Verrier determined to seek a personal interview with him.

The following account of the meeting will be read with interest.

“ On calling at the residence of the modest and unobtrusive medical practitioner, he refused to say who he was, but in the most abrupt manner, and in the most authoritative tone, began, . 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 doctor then explained what he had witnessed, and entered into all the particulars regarding his discovery. On speaking of the rough method adopted to ascertain the period of the first contact, the astronomer inquired what chronometer he had been guided by, and was naturally enough somewhat surprised when the physician pulled out a huge old watch with only minute hands. It had been his faithful companion in his professional journeys, he said; but that would hardly be considered a satisfactory qualification for performing so delicate an experiment. The consequence was, that Le Verrier, evidently now beginning to conclude that the whole affair was an imposition or a delusion, exclaimed, with some warmth, 'What, with that old watch, showing only minutes, dare you talk of estimating seconds ? My suspicions are already too well founded.' To this Lescarbault replied, that he had a pendulum by which he counted seconds. This was produced, and found to consist of an ivory ball attached to a silken thread, which, being hung on a nail in the wall, is made to oscillate, and is shown by the watch to beat very nearly seconds. Le Verrier is now puzzled to know how the number of seconds is ascertained, as there is nothing to unark them ; but Lescarbault states that with him there is no difficulty whatever in this, as he is accustomed to feel pulses and count their pulsations,' and can with ease carry out the same principle with the pendulum. The telescope is next inspected, and pronounced satisfactory. The astronomer then asks for the original memorandum, which, after some searching, is found covered with grease and laudanum.' There is a mistake of four minutes on it when compared with the doctor's letter, detecting which, the sarant declares that the observation has been falsified. An error in the watch regulated by sidereal time accounts for this. Le Verrier now wishes to know how the doctor managed to regulate his watch by sidereal time, and is shown the small telescope by which it is accomplished. Other questions are asked, to be satisfactorily answered. The doctor's rough drafts of attempts to ascerta'n the distance of the planet from the Sun from the period of four hours which it required to describe an entire diameter' of that luminary are produced, chalked on a board. Lescarbault's method, he being short of paper, was to make his calculations on a plank, and make way for fresh ones by planing them off. Not being a mathematician, it may be remarked he had not succeeded in ascertaining the distance of the planet from the Sun.

iii:

“The end of it all was, that Le Verrier became perfectly satisfied that an intraMercurial planet had been really discovered. He congratulated the medical practitioner upon his discovery, and left with the intention of making the facts thus obtained the subject of fresh caleulations e.”

In March or April, 1860, it was anticipated that the planet would again pass across the Sun, which was carefully scrutinised by different observers on several successive days, but no trace of it was obtained then, and in a certain sense Lescarbault's observation continues unconfirmed. However, this proves nothing, and many are prepared to regard the existence of this planet as a fact, to be fully demonstrated on some future occasion...

The following approximate elements were calculated by Le Verrier from Lescarbault's rough observations: Longitude of ascending node...

= 12° 59' Inclination of orbit ...

- 12° 10' Semi-axis major ( =0)

= 0.143 Daily heliocentric motion

= 18° 16' Period ... .

- 19d 17h Mean distance ...

= 13,082,000 miles. Apparent diameter of O from Vulcan...

= 3° 36'
Do.
do.

do. ( = 1) = 6.79 Greatest possible elongation ... ... ...

The application of Kepler's third law yields, as has already been shown, a result sufficiently consistent with the results in the cases of the other planets to demand attention; but, as will now be seen, some additional evidence can be adduced as to the reality of the discovery, much as it has been called in question.

On March 20, 1862, Mr. Lummis, of Manchester, was examining the Sun's disc, between the hours of 8 and 9 A.M., when he was struck by the appearance of a spot possessed of a rapid proper motion. He called a friend's attention to it, and both remarked its sharp circular form. Official duties most unfortunately interrupted him, after following it for 20m; but he had not the slightest doubt about the matter. The apparent diameter was estimated to be about 7", and in the 20m it moved over about 12' of arc. The telescope employed was 24 inches in aperture,

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Epitomised from the North British Review, vol. xxxjii. pp. 1-20, August, 1860. A full account will also be found

in Cosmos, vol. xvi. pp. 22-8, 1860; see also Cosmos, same vol. pp. 50-6.

and was charged with a power of 80. Mr. Lummis communicated with Mr. Hind on the subject of what he had seen; and the latter, by the aid of the diagram sent, determined that 12 was too great an estimate of the arc traversed by the spot in the time, and that 6' would be a nearer valued

Two French calculators deduced elements from Lummis's observations: the orbits which they obtained, though necessarily very imperfect, are fairly in accord both with each other, and with Le Verrier's earlier orbit.

The first result is adopted from Valz's elements, the second from Radau's.

I.
Longitude of ascending node

2° 52'
Inclination of orbit... ...

10° 21' Semi-axis major ( = 1.0)...

0.132 ... 0.144 Daily heliocentric motion ...

= 20° 32' 1895 Period

- 170 136 ... 194 22h Mean distance in miles ...

= 12,076,000 ... 13,174,000

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From the heliocentric position of the nodes, it appears that transits can only occur between March 25 and April 10 at the descending, and between September 27 and October 14 at the ascending node.

Instances are not wanting of observations of spots of a planetary character passing across the Sun which may turn out to have been transits of Vulcano. The following are a selection of these instances.

On October 10, 1802, Fritsch, at Magdeburg, saw a round spot pass over the Sun. In 3m it had moved 2', and after a cloudy interval of 45 had disappeared.

On October 9, 1819, Stark, at Augsburg, saw a well-defined and truly circular spot, about the size of Mercury, which he could not find again in the evening.

d Month. Not., vol. xxii. p. 232. April 1862. Lummis's observations were very severely criticised by Prof.C.H.F.Peters, who claimed to have identified Lummis's "planet" beyond question with a particular Sun-spot recorded by himself in

America and by Spörer in Europe. (Ast.
Nach., vol. xciv. No. 2253, April 16, 1879.)
Certainly Peters's argument is strong.

Month. Not., vol. xx. p. 100. Jan. 1860; also pp. 192-4. March, 1860; Webb, Celest. Objects, p. 40.

On October 2, 1839, Decuppis, at Rome, saw a perfectly round and defined spot moving at such a rate that it would cross the Sun in about 6 hours f.

On October 11, 1847, Schmidt saw a small black point rapidly pass across the Sun.

On March 12, 1849, Lowe and Sidebotham watched for half an hour a small round black spot traversing the Sun.

On October 14, 1849, Schmidt saw a black body, about 15" in size, pass very rapidly from East to West before the Sun. " It was neither a bird nor an insect.”

In the works whence these instances are cited, others are given; but, though suspiciously suggestive of planets, the dates do not come within the necessary limits for them to have been apparitions of Vulcan, so it is not worth while to transcribe them; but nevertheless they are interesting, and worthy of attention.

Fig. 45 will be useful, if for no other purpose, as a warning to observers not to jump too hastily at conclusions as to what they see with their telescopes. On November 30, 1880, M. Ricco at Palermo, whilst making his customary daily observations of Sunspots with a telescope of 31 inches aperture, saw a swarm of black bodies slowly traverse the Sun's disc. He thought at first that he had the singular good fortune to be gazing on a shower of meteors, but sustained attention revealed the fact that the objects seen were evidently birds with wings. Subsequent consultation with certain zoologists rendered it tolerably clear that what M. Ricco saw was a swarm of cranes. Some calculations, the details of which need not be gone into here, imply that they were flying at an elevation of 5 | miles h.

It is right here to state that M. Liais asserts that being in Brazil he was watching the Sun during the period in which Lescarbault professes to have seen the black spot, and that he is

' Comptes Rendus, vol. ix. p. 809. 1839.

E. Ledger's Lecture on Intra-Mercurial
Planets, 8vo. Cambridge, 1879.

* For an exhaustive summary of all the recorded observations of black ob jects seen on the Sun, see the Rev.

L'Astronomie, vol. vi. p. 66. Feb. 1887.

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