As a small-time restorer of vintage clocks, I can advise that a "fusee"
is a simple conical pulley and chain or cord drive which compensates for
the reducing torque from a spiral spring as it runs down.  The spring is
usually in a plain drum which has the chain or cord wound around which is
then attached to a spiral conical pulley so that the diameter (and thus
mechanical advantage) increases as the drum turns during run down.

This technique has been used in quality spring clocks and watches for
maybe 200 or more years to keep a constant drive power, similar to that
from weights, without the limitations.  Obviously it has uses in other
spring driven devices like music boxes.

Cheers,
Darrell Clarke,
Adelaide, Australia