The brothers Friedrich and Carl Wilhelm Siemens…

The brothers Friedrich and Carl Wilhelm Siemens invent the regenerative furnace, initiating the development of the open hearth steel-making process.

This furnace operates at a high temperature by using regenerative preheating of fuel and air for combustion.

The two German-born engineers had claimed in 1857 to be recovering enough heat to save 70-80% of the fuel.

Through this method, an open-hearth furnace can reach temperatures high enough to melt steel, but the Siemens brothers do not initially use it for that.