[Capt. Tom]

Princeton edu-
Vulcan was a small planet proposed to exist in an orbit between Mercury and the Sun. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French mathematician Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan. No such planet was ever found, and Mercury's orbit has now been explained by Albert Einstein's theory of general relativity.

[Red Badger]

...Verrier hypothesized that they were the result of another planet, which he named Vulcan. No such planet was ever found

[Verginius Rufus]

Le Verrier may have been wrong about Vulcan, but he is credited with the discovery of Neptune. He calculated the location of a planet beyond Uranus, sent the information to an astronomer, Johann Galle, at an observatory in Berlin, and Galle found Neptune within an hour within one degree of where Le Verrier predicted it would be. That was in 1846 and Neptune takes 164.8 years to go around the sun once, so it is now very close to where it was when it was discovered.