What ingenious device did Watt propose in 1765 to solve the excessive heat loss?

Answer

The separate condenser

Watt's flash of genius was the separate condenser, where spent steam was routed to a separate, permanently cold chamber for condensation, allowing the main cylinder to remain hot.

What ingenious device did Watt propose in 1765 to solve the excessive heat loss?
inventionSignificanceengineSteamWatt