fusee - n.  An ancient and elegant method of producing constant torque
from a variable torque power source.

This is a pair of drums wrapped with a chain which transfers the power
from a spring on the shaft on the first drum to the gear train operating
from the second drum.  Since it was historically difficult to build a
clock spring giving equal torque from fully wound all the way to
unwound, one or both of these barrels was given a conical form.

When the spring is wound tight, little of the chain is on the spring
drum; the chain is attached to the large end of the conical section and
wraps will wrap smaller and smaller, filling the drum.  From there the
chain goes over to the other drum and attaches at the small end of the
conical section and will wrap larger and larger.

*** the following is an attempt at ASCII illustration ***

                                   ___________
             ||                    | spring   |
             ||                    |  case    |
            ----                   ------------
           oooooo                   ----------
          oooooooo                   --------
         oooooooooo                   ------
        oooooooooooo                   ----
       ooooooooooooooooooooooooooooooooooo
             ||                         ||
         driven shaft
          and gears

    (No, Virginia, this is Not a Christmas Tree.)

One problem with searching the Web for "fusee" is that you get lots of
stuff about clocks that _use_ fusees, information on rockets (French call
them that), and occasional notes on self-igniting flares such as those
you're supposed to carry in your car for emergencies.

Karl Petersen

 [ *** If this illustration doesn't resemble two Christmas trees (the
 [ one on the right is upside-down), then the "Display Font" option of
 [ your e-mail viewer should be set to a monospaced font such as
 [ Courier.  Karl's picture is cute!  -- Robbie