Spit Jacks and Bottle Jacks
The low-tech and most common method for roasting meat was to hang the haunches and poultry from metal hooks over the flames. (see image below left) The cook or assistant cook manually turned and moved the meat to the desired temperature zones as needed. More commonly, however, young servant boys or girls would be tasked to stand by the fire and manually turn the hand crank for hours on end. The much busier and more important cook and assistant cook oversaw the process, leaving the physical work to the child.
The most infamous type of early method was the turnspit dog (see drawing below right). A wall-mounted circular cage secured a small dog (usually a terrier mutt) who would run akin to a hamster in a wheel, providing the power source turning the roasting spit. The poor animal would run as long as was required to fully roast the meat. This was a pre-industrial device considered an improvement over exhausting a young child. Thankfully, both methods were obsolete by the end of the 18th century.
Far superior was the invention of devices known broadly as roasting jacks. These devices turned the meat in some sort of automated fashion and were not only fabulous time and labor savers, but also evenly cooked the meat. There were a variety of roasting jack types: hand crank, clockwork jack, bottle jack, spit-jack. Some of these were quite simple, while others were huge and complex.
The clockwork spit-jack (four examples below) was a vast improvement in technology. A weight attached to a string worked by gravity and needed to be re-wound periodically using a hand-crank. By far the most common automated jack, there were dozens of makers with a wide variety of styles.
A far better option was the bottle jack (example below left) which derived its name from the shape: the mechanism is housed inside a brass cylinder shaped like a bottle. It was an improvement over the clockwork jack-spit because it was spring driven, wound by a key, and ran for a longer length of time before needing to be re-wound.
The meat swung in a gentle clockwise and counterclockwise rotation, and if used in conjunction with a half-barrel, metal reflecting-oven or screen (example below right) facing the fire, an even heat radiating from several sides resulted in better roasting in a shorter amount of time. The latter meant it was also an efficient use of fuel.
The larger the fire area, the more roasting racks and spits there would be. In the image below from a historic house in Bristol, the spit-jack is the brass object mounted in the upper right corner of the fireplace mantle, the dangling weight pulley turning the meat in the metal rack inside the fireplace and over the flames (if there were flames). Off to the right is a bottle jack mounted on a black metal half-barrel screen.