Globus Aerostaticus, the hot-air balloon:

Originally created by French astronomer Joseph Jerome le Francais de La Lande in 1798 to honor the hot-air balloon, which was considered a scientific breakthrough of the time. The constellation was composed of dim stars that were located between Capricornus, the sea-goat, and Microscopium, the microscope. Although the constellation appeared in several star atlases, in never became official and fell out of use by astronomers.