This ingenious piece of equipment is in the kitchen of Wordsworth House at Cockermouth. The fire causes air to expand, become less dense and rise up the chimney. In other words, it gives kinetic energy to the air. Part way up the chimney, there is a small horizontal windmill. The rising hot air turns this. It drives the gearing mechanism shown in the top two pictures which then turns the roasting spit at the bottom to make sure that the mean is evenly roasted by the fire. So wasted energy from the fire is used to drive the mechanism. It makes the fire much more efficient.
