A fusee drive is a method of providing power, originally to clocks,
musical clocks playing bells, and barrel organs, and also used for early
musical box movements, especially the musical clock movements found in
the base of clocks, as well as musical boxes up to the early 1800's.

The fusee was used in clocks as early as 1525 A.D. (Jacob Zech of Prague
was said to have invented the fusee, although some earlier fusee clocks
of German make have been found).

It consists of a conical-shaped drum connected to the mainspring barrel
by a chain or gut string.  The conical shape was found to maintain the
force of the spring at a consistent level while the power from the source
(a weight or a  mainspring) varied from strong (when fully wound) to weak
(when unwound).

The mechanism was wound using the fusee barrel which, in turn, wound the
spring barrel.

Musical boxes after the early 1800's eliminated the fusee drive and used
a directly-wound spring barrel (cheaper to manufacture!).

Bill Wineburgh
http://members.aol.com/WWineburgh/musicbox.html