Airshipcat:

1878:

July 29: During the solar eclipse, Watson (Michigan) and Swift, at the Warner observatory, observed red discs of 800 meters of diameters at 32000 km de la Terre [Fort]. [1]

But Vulcan did not disappear entirely. Like the alleged moon of Venus (reported up to 1791) or Houzeau's planet Neith (an amazing discovery by the astronomer who could not identify Mercury), Vulcan continued to exist in the scientific journals and textbooks, if not in the heavens. On July 29, 1878, a total eclipse of the Sun took place.

Prof. James C. Watson was interested in searching out Vulcan during this eclipse. If Vulcan would not reveal itself by crossing the Sun's disc, when LeVerrier predicted, it might be seen near the eclipsed Sun. Watson memorized the positions of all stars which would be around the Sun during the eclipse. If there was another bright object, he would be able to identify it as Vulcan. Watson advised Prof. Asaph Hall of the U.S. Naval Observatory in Washington that he had seen an unknown object while watching the eclipse at Separation, Wyoming:

"I have the honor to report that at the time of totality, I observed a star of the four and four and a half magnitude in R.A. 8h. 26m. dec. 18 north, which is, I feel convinced, an intra-Mercurial planet.... There is no known star in the position observed..."

Prof. Lewis Swift of the Dearborn Observatory watched this eclipse near Denver and said that he saw two unknown objects. As no one else watching the eclipse noticed any Vulcans, Swift's double observation and that of Watson's were critically questioned and soon discredited. According to the French astronomer Flammarion, the unknown objects were the stars Theta and Zeta in the constellation of Cancer; but this explanation is incomplete. The positions given by Watson and Swift did not agree with each other, meaning that at least three unknown objects as bright as planets had been reported by these professors.

With Vulcan having failed to cross the Sun when expected, and seen only during eclipses of the Sun by astronomers whose reputations were ridiculed, Mercury's advances remained a puzzle -- until Einstein. [2]

[27.01] James Craig Watson, First Director of Washburn Observatory: His Obsession with the Intra-Mercurial Planet Vulcan

W. Sheehan (Hutchinson, MN)

The first director of the Washburn Observatory, Watson began his career at the University of Michigan, where he discovered more than a score of asteroids and planned (but did not live to carry out) the first search for a trans-Neptunian planet. He became a strong supporter of Le Verrier's hypothesis that a planet closer to the Sun than Mercury (Vulcan) was causing the anomalous advance of 38" of arc per century of Mercury's perihelion, and mounted a special search for Vulcan at the July 29, 1878 total eclipse, at Separation, Wyoming, recording two strange reddish stars near the Sun; which he assumed were intra-Mercurial bodies. With the exception of Lewis Swift at Denver, Colorado, no one else confirmed his observations, and they were sharply criticized by Clinton College (New York) astronomer C. H. F. Peters. Nevertheless, Watson remained absolutely convinced of what he had seen, and his move from Ann Arbor to Madison in 1879 was partly motivated by the prospects of obtaining better instruments with which to further his search for Vulcan, which became the obsession of his later years. He was in the process of constructing an underground solar observatory from which he hoped to see stars near the Sun in broad daylight when he died, unexpectedly, in 1880. Though it is now known that Vulcan does not exist, Watson's observations at the July 1878 eclipse remain problematic; it is probable that he observed at least one and possibly two pygmy comets in the neighborhood of the Sun. [3]

There was one more flurry after the total solar eclipse at July 29 1878, where two observers claimed to have seen in the vicinity of the Sun small illuminated disks that could only be small planets inside Mercury's orbit: J.C Watson (professor of astronomy at the Univ. of Michigan) believed he'd found TWO intra-Mercurial planets! Lewis Swift (co-discoverer of Comet Swift-Tuttle, which returned in 1992), also saw a 'star' he believed to be Vulcan -- but at a different position than either of Watson's two 'intra-Mercurials'. In addition, neither Watson's nor Swift's Vulcans could be reconciled with Le Verrier's or Lescarbault's Vulcan.

After this, nobody ever saw Vulcan again, in spite of several searches at different total solar eclipses. And in 1916, Albert Einstein published his General Theory of Relativity; which explained the deviations in the motions of Mercury without the need to invoke an unknown intra-Mercurial planet. In May 1929 Erwin Freundlich, Potsdam, photographed the total solar eclipse in Sumatra, and later carefully examined the plates that showed a profusion of star images. Comparison plates were taken six months later. No unknown object brighter than 9th magnitude was found near the Sun.

But what did these people really see? Lescarbault had no reason to tell a fairy tale, and even Le Verrier believed him. It is possible that Lescarbault happened to see a small asteroid passing very close to the Earth, just inside Earth's orbit. Such asteroids were unknown at that time, so Lescarbault's only idea was that he saw an intra-Mercurial planet. Swift and Watson could, during the hurry to obtain observations during totality, have misidentified some stars, believing they had seen Vulcan. [4]