smokejack

from The Century Dictionary.

• noun A machine for turning a roasting-spit by means of a fly-wheel or -wheels, set in motion by the current of ascending air in a chimney.
• noun On railways, a hood or covering for the end of a stove-pipe, on the outside of a car. Also called stove-jack.

from the GNU version of the Collaborative International Dictionary of English.

• noun A contrivance for turning a spit by means of a fly or wheel moved by the current of ascending air in a chimney.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A device for turning a spit by means of a fly or wheel moved by the current of ascending air in a chimney.