Pear-shaped glass vessel with central brass spike and threaded brass collar, covered by a cap. The outer half of the flask is covered with lead foil (originally tin foil).

This device was used to simulate the aurora borealis phenomenon. The flask was connected to an air pump and partially evacuated. It was then electrified by means of the prime conductor of an electrical machine. The glow produced at the spike, which greatly resembled an aurora borealis, behaved differently for positive and negative electrical charges. Provenance: Lorraine collections.