Today the curators bring us three devices from the shelves of the Cabinet of Physics. All are induction coils, sometimes called "spark coils." Each is a transformer. Each takes a low voltage, with input interrupted in on-and-off-and-on-and-off fashion, and converts it to a much higher voltage, high enough to produce a series of substantial sparks across an air gap.
Induction coils become supporting players in a number of other videos from the Cabinet. The pulsed high voltage produced by these induction coils is a useful tool for investigating complex electrodynamic and electromagnetic phenomena that featured prominently in late 19th-century physics. One example is the colorful Geissler discharge tube we see as the third coil, the mighty Ruhmkorff coil, is demonstrated. The high-voltage pulses pass through low-pressure gas sealed within the glass tube.
The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique scientific demonstration instruments. The Foundation's homepage may be found here, and its Youtube channel, florencefst, here.