Leonardo da Vinci’s mechanical device intended to turn a roast evenly over a fire was a roasting jack.
A roasting jack rotates meat on a spit so that heat reaches it more evenly. Leonardo’s design used mechanical power transmitted through gears and a propeller-like rotor exposed to rising hot air. As heated air moved upward, it could turn the rotor, which then drove the spit through the gearing.
The device illustrates Leonardo’s interest in converting natural forces into useful work. Instead of requiring a cook to turn the spit continuously by hand, the mechanism could use the airflow produced by the fire. The arrangement also demonstrates his understanding of gears, rotational motion, and the practical value of automation in household tasks.
Leonardo did not invent the general roasting spit or every type of roasting jack. Earlier turning devices existed, and later roasting jacks used springs or weights. His version is notable for applying hot-air movement and mechanical gearing to automatic rotation.