Watches + Dictionary = Watchionary
Richard Lange Tourbillion ‘Pour le Mérite’, www.alange-soehne.com
Fusée and Chain
It is a type of transmission system used in some mechanical watches to help maintain a consistent rate of power delivery to the movement. It consists of a cone-shaped pulley, called a fusée, and a fine chain that connects the fusée to the mainspring. As the mainspring unwinds, the chain transfers power to the fusée, which helps maintain a consistent rate of power delivery even as the mainspring winds down.