Controlled-flame furnace

"The more the natural movement of the fire lasts, the more its action will be powerful"

This furnace was drawn in section by Leonardo. It melts various types of metals, with different melting points. The metals are positioned in crucibles placed at a distance proportional to the melting point and not directly exposed to the flame. The air-intake opening which feeds the fire is located at the base of the furnace.
Codex Atlanticus, sheet 87
1478-1480