Sun > Vulcan > Mercury

Vulcan was the name given to a hypothetical Intra-Mercurial planet on March 26, 1859 by amateur astronomer M. Lescarbault, a doctor of Orgeres, near Orleans, France. On January 25th 1896, M. Lescarbault was given the decoration of Legion of Honour by Napoleon III for his alleged discovery. The discovery was then challenged by astronomer Liais of Brazil who claimed to have an even more powerful telescope, by which yielded no such results of an Intra-Mercurial planet.^[1]

History

On January 2, 1860, Urbain J. J. Leverrier, at the time Director of the Observatory of Paris, and world-famous as one of the discoverers of Neptune, read a paper to the Academie des Sciences in which he pointed out that the observed motion of Mercury did not agree with theory. This anomaly, it may be noted, has since become one of the pillars of Einstein’s theory of relativity. At the time, Leverrier proposed to explain it by assuming that matter, as yet undiscovered, existed in the sun’s neighbourhood — in other words, that one or more small planets probably revolved somewhere in the space between Mercury and the sun.

There are, of course, two planets known to revolve round the sun at a less distance than we ourselves do — Venus, the beautiful twin-sister of our own world, which we know as a morning or evening star, and Mercury, which is smaller and far more difficult to see. It was natural that Leverrier, who had himself added an extra-Uranian planet to the Solar System, should have felt that there was no a priori reason against the existence of an intra-Mercurial one. On the other hand, it naturally seemed rather curious that, if a planet large enough to cause the observed disturbances really existed so close to the sun, this should not have been discovered earlier. He announced his conclusion with diffidence, remarking:

“This result naturally filled- me with inquietude. Had I not allowed

some error in the theory to escape me? New researches, in which every

circumstance was taken into account by different methods, ended only

in the conclusion that the theory was correct, but that it did not agree

with observations. . . . Does it [the undiscovered matter near the sun]

consist of one or more planets, or other more minute asteroids, or only of

cosmical dust? The theory tells us nothing on this point.”

It is a singular fact that when Leverrier read this paper he had (or might have had) in his pocket a letter which he had received on December 22, 1895 from one M. Lescarbault, a doctor of Orgeres, near Orleans, who was also an amateur — a very amateur — astronomer. This letter announced the discovery of an intra-Mercurial planet. Lescarbault stated that on March 26, 1859, he had seen a round black spot, apparently a planet in transit, moving across the upper part of the sun’s face on a path which slanted upwards. It had remained in view for an hour and a quarter, during which time it had progressed for a distance rather less than a quarter of the sun’s diameter. Very shortly after reading his paper, Leverrier went to Orgeres — apparently with the intention of exposing an impostor.

Leverrier went down to Orgeres in a state of considerable irritation. The meeting has been inimitably described by R. A. Proctor:

“. . . The interview was a strange one. Leverrier was stern and, to say

the truth, exceedingly rude in his demeanour,

‘So you are the man,’ said Leverrier, looking fiercely at the doctor,

‘who pretends to have seen an intra-Mercurial planet. You have com-

mitted a grave offence in hiding your observation, supposing you really

have made it, for nine months. Tell me at once and without equivocation

what you have seen.’

“Lescarbault described his observation...

Leverrier then examined the doctor’s telescope, and presently

asked for the record of the observations. Lescarbault produced it,

written on a piece of laudanum-stained paper which at the moment

was doing service as a marker in the Connaissance de Temps.

“Leverrier asked Lescarbault what distance he had deduced for the

new planet. ‘The doctor said, ‘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 adjourning to the carpenter’s shop, they found the board with its

lines and its numbers in chalk still unobliterated.

“This last piece of evidence, satisfied him as to the good faith of the

doctor of Orgeres. With a grace and dignity full of kindness, which must

have afforded a singular contrast to his previous manner, he congratulated

Lescarbault on his important discovery.

“M. Rouland, the Minister of Public Instruction, communicated to

Napoleon III the result of Leverrier’s visit, and on January 25th the

Emperor bestowed on the village doctor the decoration of the Legion of

Honour.”

“Leverrier... lost no time in performing the necessary calculations which

that worthy had found so baffling. He obtained, for the new planet’s mean

distance from the sun, about 13,000,000 miles, and for its period of

revolution 19 days 17 hours. Lescarbault, who had seen Mercury in

transit over the sun with the same telescope, and the same magnifying

power, on May 8, 1845, considered that the new planet (which he

decided to name “Vulcan”) had a disc rather less than a quarter as large.

Accordingly, Leverrier calculated that Vulcan’s volume was probably

about one seventeenth that of Mercury. It did not escape him that,

supposing its mass to be in anything like the same proportion, Vulcan

could not be held responsible for more than a small fraction of the dis-

turbances observed to be taking place in Mercury’s orbit.

“He also calculated that Vulcan ought to be in transit on the sun’s face

on or about April 3rd and October 6th of every year, at which times it

should, of course, be visible in the same manner as it had been to Lescar-

bault. He did not hold out much hope of its being seen at other times,

since he computed that its lustre would be so feeble that it might easily

remain unseen, even during a total eclipse of the sun.

“The existence of Vulcan did not remain unchallenged for long. Shortly

after Lescarbault had been decorated, news arrived from Brazil that

another astronomer, Liais, whose [supposed] observations "exactly" coincided, in point

of time, with Lescarbault’s, had been examining the same part of the sun

with a "more powerful telescope", and had seen no vestige of any such spot

as Lescarbault had described.”

References