Figure 77 is a reproduction of an engraving from an old source depicting an electrostatic machine.
It consists of a horizontal glass cylinder, rotated by a handle on its longitudinal axis. The cylinder's axis is held on two glass supports which also act as insulators. On either side of the glass tube are two separate, cylindrical brass conductors, supported by two glass columns, parallel to its axis and on the same horizontal plane. A leather pad attached to one of the conductors rubs against the glass when the cylinder is rotated and collects a negative charge.
Extending from each conductor is a curved rod with a small ball at the end. These are positioned close to one another, and it is between these balls that an arc is struck when the machine is energized.