This long copper rod has a pointed end and an insulating wooden handle.
If the tip of the rod is brought close to the terminal of an electrostatic machine (for example the capacitor of the Holtz machine 17ME), on which the positive or negative charge produced by the machine has accumulated, by induction the rod acquires a charge of the opposite sign to that on the terminal and sparks fly between the two. The phenomenon is explained by the build-up of a greater charge density on the pointed parts of conducting materials. Around a point there is such an intense electric field that electrons pass through the thin layer of air, which becomes ionized and produces the flash of the spark.

Device on display.