Invented in 1906! Before electronic ignition, this is how the distributor made a 15kV spark from a 6V or 12V system.
The pushbutton simulates the action of the "point" contacts, which were opened by the mechanical distributor when it was time to fire a spark plug. Notice that the faster you push it, the lower the spark produced. This is called "dwell", and it's why power could drop off at higher RPMs. It's also why tune-ups every 3000 miles weren't optional; it needed lots of adjustment.
