The middle of three wheels, which simply conveys the motion of one outside wheel to the other outside wheel.
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Suppose A, B, C to be three wheels, B being the idle or gear wheel. B simply conveys the motion of A to C, or of C to A.
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Entry taken from Dictionary of Phrase and Fable, edited by the Rev. E. Cobham Brewer, LL.D. and revised in 1895.
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