point around which all the primary planets revolve. It must not be supposed, however, that the Polish astronomer attained to our existing amount of knowledge on the subject. Far from it: his ideas were defective in more than one important particular. In order to account for the apparent irregularities in the motions of the planets, as seen from the Earth, he upheld theories which subsequent advances in the science showed to be unnecessary and to rest on no substantial basis. Amongst other things he retained the theory of Epicycles. The ancients considered that the planetary motions must be effected uniformly and in circles, because uniform motion appeared the most perfect kind of motion, and a circle the most perfect and most noble kind of curve. There is at any rate a reverential spirit in this idea which, notwithstanding our enlightenment, we need not despise. Copernicus announced his system in a treatise entitled De Revolutionibus Orbium cœlestium, the actual publication of which, in 1543, he only just lived to see, for he died the same year; for him this was perhaps fortunate rather than otherwise, because the work was condemned by the Papal Congregation of the Index.' Had it been possible for the reverend gentlemen who formed that body to have got the author within their clutches, it is more than likely that he would have suffered as well as his book; as did Galileo after him.

Tycho Brahe was the last great astronomer who ventured on any original speculations in this field. Influenced either by bona fide scruples resulting from an erroneous interpretation of certain passages in Holy Scripture, or it may be, simply by a desire to perpetuate his name, he chose to

Fig. 43.

THE TYCHONIC SYSTEM.

regard the Earth as immoveable, and occupying the centre of the system: the Moon as revolving immediately round the Earth:

and, exterior to the Moon, the Sun doing the same thing-the various planets revolving round the latter as solar satellites.

Kepler and Newton finally set matters right by perfecting the Copernican system, and so negativing all the others; yet down to quite recent times there have survived on the part of utterly ignorant people remnants of disbelief (real or professed) in the Copernican system, but even the most cursory examination of these remnants would be most unprofitable.

**One of these dials was taken out of the wall about 1844,
and presented to the Royal Society.

CHAPTER III.

VULCAN (?).

Le Verrier's investigation of the orbit of Mercury.-Narrative of the Discovery of Vulcan.-Le Verrier's interview with M. Lescarbault.-Approximate elements of Vulcan. Concluding note by Le Verrier.-Observations by Lummis at Manchester.-Instances of Bodies seen traversing the Sun.-Hind's opinion.-Alleged Intra-Mercurial planets discovered in America by Watson and Swift on July 29, 1878.

BEFORE 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 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 ».

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

A

1859.

Compt. Rend., vol. xlix. p. 379.

b Objections to this theory are stated

in detail by Newcomb in Astron. Papers for use of Amer. Naut. Almanack, vol. i. 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 mark 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 savant 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.

'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 calculations "."

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:

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 2 inches in aperture,

с

Epitomised from the North British Review, vol. xxxiii. 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.