The instrument serves to show the different types of electrical discharge that are generated in air when pressure is reduced.
It consists of a glass tube closed at the ends by brass caps and mounted on a wooden base. Inside the tube there are two brass rods, each with a ball at the end, which form the spark gap.
The brass fitting at the base has a tap.
By placing the base of the instrument on the plate of a pneumatic machine, air may be extracted from the tube, which at the same time is connected to an electrostatic machine. The type of electrical discharge that occurs between the spark gap electrodes may be observed as the pressure inside the tube changes.
The instrument was acquired in 1809 or 1810.
Instrument on display.
