Mills take the power from running water, like a river, and turn it into machine-power to run machines that can do many tasks.
The most important part of the mill is the waterwheel, which is what takes moving water and transforms its power into something machines can use. The waterwheel is placed in the flow of water, either above or below it, with paddles which are hit by the water as it runs into the wheel. By pushing these paddles, the force of the water makes the wheel turn. The centre of the wheel is mounted on an axle which turns with the wheel and transfers the energy of the wheel turning to machinery (Tyrwhitt, 35-38).
While Paris has two good rivers to use for water power, mills weren’t usually built directly on the river because they needed a steady source of water. The water of a river rises and falls with the tide, which means that water-powered machinery would be able to perform different amounts of work at different times of the day. It was much more efficient for machinery to work at a steady level at all times, which meant that the flow of water needed to be consistent. The solution to this was the mill-race, or raceway: a channel of water redirected from a dammed river, with special machinery which regulated the flow of water so that the mill-race provided a steady amount of water all day. In Paris, Capron built and leased most of the earliest raceways; mill-owners leased rights to use Capron’s raceways so that they could build their mills along them instead of on the river.