Twin

This is a high quality mechanism, cleaned and repaired, of a twin fusee striking bracket clock circa 1900. The interested feature is the fusee gear both for the time train and the striking train.  This is just visible on the left hand side with the wire wound around the barrel pulling on the conical gear above. This sort of gear was first designed to solve a problem. The problem is straightforward, even if the solution is not; as a fully coiled mainspring unwinds, the torque it produces decreases. This effect can be seen clearly with a clockwork toy car. Fully wound, it scoots away, but instead of maintaining the same speed until the spring has completely unwound, it gradually slows, the spring's torque decreasing.  The idea goes something like this; rather than letting the mainspring drive the mechanism directly, a vaguely conical tube with a spiralled groove (the fusee) is placed in between. A chain, wrapped around the fusee, joins it to the mainspring. As the mainspring unwinds, it pulls the chain from the fusee, turning it as it unwraps. The clever part comes from the shape of fusee itself. It isn't a simple conical shape, having a profile more like the bell of a trumpet, which is calculated specifically for the torque characteristics of the mainspring. Think of it like the gears of a bicycle; the smaller the driven cog, the harder it is to turn. This is because the leverage on the axle is less, and so more torque is required. The fusee is effectively a continuously variable gear, its diameter increasing as the spiralled chain unwinds, requiring less torque to turn it and therefore compensating for the torque loss in the mainspring.
The theory is great but while the British adopted the technology, the French largely did not. French nineteenth century mechanisms were of a high quality and very accurate despite not having fusee gears.