The bracket clock represented a major breakthrough in British clock making; it was one of the first clocks to use mainsprings as its power source and thus enable the clockmakers of the day to produce smaller, portable table clocks that could be used in multiple rooms in the house.
Previously in early clocks, the driving force was provided by a weight on a line or rope wrapped around a rotating barrel. This can be compared to bucket on a wishing well, the weight of the bucket providing a rotational force to the winch if pressure on the handle was released. The weight driven clock is similar, and all that is needed is a means of releasing the weight at a controlled rate and you then have a timekeeper. This system has some advantages, it is cheap and easy to produce and it provides a constant force which was important to good time keeping. It is for these reasons that the weight driven clock continues to be produced to the present day.
The weight driven clock did have a couple of disadvantages though. Firstly, the clock was not portable and secondly, the clock had to be mounted at a reasonable height to allow for weights to descend and therefore provide duration.
The invention of the clock main spring dramatically changed clock making. It is believed mainsprings appeared in the first spring powered clocks as early as the 15th century in Europe. The first mainsprings were made from a strip of steel that was not hardened, and had very limited duration. Clock mainsprings were made in a coiled form and were fitted into barrels.
One of the drawbacks of using a coiled spring as the driving force in a clock is that it produces more power when it is fully wound compared to when it is partially wound. This problem was overcome to a large extent by the invention of the fusee.
The fusee is a conical shaped device with a grove cut in it. In the grove, a gut line or chain is wrapped around the fusee and the other end wrapped around the mainspring barrel. At one end of the fusee shaft is the winding square and at the other is a gear that drives the clock train.
The idea being that when the mainspring is fully wound the line or chain is acting on the smaller diameter end of the fusee. As the clock train runs, the line unwinds from the fusee and winds back onto the spring barrel, so when the spring is fully wound it is acting on the smallest diameter of the fusee and when the spring is less wound it is acting on the largest diameter section of the fusee.
This has the effect of evening out the power applied to both the clock, critical for timekeeping, and the strike train which helps to produce an even speed for the striking of the bell.
The invention of the fusee revolutionised clock and watch making in Great Britain, and gave rise to the production of many beautiful table or bracket clocks, and pocket watches.