I
Ancient Roman god of fire.
He was the counterpart of the Greek Hephaestus . Vulcan was especially associated with the destructive aspects of fire, such as volcanoes or conflagrations, and for this reason his temples were usually located outside the city. His chief festival, the Volcanalia, was marked by a rite in which the heads of Roman families threw fish into the fire. Often invoked to avert fire, he was addressed with epithets such as Mulciber ("Fire Allayer").
II
Hypothetical planet within the orbit of Mercury .
It was predicted in 1859 by Urbain-Jean-Joseph Le Verrier (1811–77) to account for an unexplained component of the precession of Mercury's orbit. Sightings were reported between 1859 and 1878, but these were not confirmed subsequently by observations made either during solar eclipses or when the planet was predicted to cross the Sun. The anomalies of Mercury's orbit were later explained by relativity .