Roasting jack

A roasting jack is a machine which rotates meat roasting on a spit. It can also be called a spit jack, a spit engine or a turnspit, although this name can also refer to a human turning the spit, or a turnspit dog. Cooking meat on a spit dates back at least to the 1st century BC, but at first spits were turned by human power. In Britain, starting in the Tudor period, dog-powered turnspits were used; the dog ran in a treadmill linked to the spit by belts and pulleys. Other forms of roasting jacks included the steam jack, driven by steam, the smoke jack, driven by hot gas rising from the fire, and the bottle jack or clock jack, driven by weights or springs.

A great majority of the jacks used prior to the 19th century were powered by a descending weight, often made of stone or iron, sometimes of lead. Although most commonly referred to as spit engines or jacks, these were also termed weight or clock jacks (clock jacks was the more common term in North America).

Earlier jacks of this type had a train of two arbors (spindles), later ones had a more efficient three arbor train. In the case of British examples, almost without exception, the governor or flywheel was set above the engine (as opposed to being located within the frame) and to one side; to the right for two train and to the left for three train engines.

European jacks are characterised by a flywheel set centrally and often within the frame; commonly the highest part of the frame has a bell-like arch that the shaft for the flywheel passes through.

A steam-powered roasting jack was first described by the Ottoman-Turkish polymath and engineer Taqi al-Din in his Al-Turuq al-samiyya fi al-alat al-ruhaniyya (The Sublime Methods of Spiritual Machines), in 1551. A steam-powered turnspit was also briefly mentioned by John Wilkins in his book Mathematical Magick (1648). A steam-driven jack was patented by the American clockmaker John Bailey II in 1792, and steam jacks were later commercially available in the United States.

Leonardo da Vinci sketched a smoke-jack in the form of a turbine with four vanes. Smoke-jacks were also illustrated in Vittorio Zonca's book of machines (1607), and in Wilkins's Mathematical Magick. The 1826 A Treatise of Mechanics describes a smoke-jack:

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