The Frenchman Le Verrier, thanks in part to the successful discovery of the planet Neptune thanks to orbital perturbations on Uranus, suggested the presence of a planet, which he named Vulcan, inside Mercury’s orbit, which would explain the orbital perturbations, which were indeed present. The planet was never found, and today we know it doesn’t exist. The explanation would come in 1916, when Albert Einstein explained these orbital perturbations with General Relativity.
