The device is actually an electrometric tube, also known as Lane's tube or electrometer.
The specimen on display is composed of a spherical glass bottle with a long neck (diameter 14.5 cm, height 20 cm) suspended horizontally over a wooden base (35 x 13.5 cm) by an upright piece of wood, a sort of guillotine, through which the neck of the bottle is inserted.
The mobile sphere of the gap is held by a horizontal brass shaft held by a small bakelite column which is fixed onto a small wooden platform that slides between two guides, they too wooden, fixed to the instrument platform.