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Inventory no. 28877 - Former Display Label

English WORM-JACK
c.1700

Brass, and steel, with silvered brass dials. Unsigned and undated, but possibly by John Rowley.

This instrument is weight-driven. The part of the frame bearing the worm-gear is hinged at the bottom to the main structure of the frame and joined at the top by a fine screw, so that the friction between the worm and the wheel can be regulated by turning the screw. Thus the speed of the instrument can be regulated. The rotating vanes at the top also serve to control the speed.

A worm-jack may be used to drive anything requiring a rotary motion, e.g. the roasting of an animal on a spit. However, this carefully constructed instrument was probably intended for scientific purposes, and may have been used by Lord Orrery for driving astronomical models.

In Thomas Wright's catalogue of the Orrery Collection (1731), this instrument is described as "A Compound Machine on a Stand wh ye 3 Weights". Only one weight appears to have survived.

[Orrery Collection, no. 30]
Lent by Christ Church.

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