Phil and Tim -
It does seem a bit obvious... Go back 600 or 700 years... The unwashed monk in brown sack-cloth has the leadout rope. The rope's upper end attaches to an arm connected to the bell. The bell is pivoted about where the clapper hangs free.
System is in equilibrium until Quasimodo pulls his rope. Bell swings. Momentum returns it - past equilibrium point. Eventually, repeats of the above cause the bell to hit the clapper.
BONG!
Repeat as desired, or directed...
In this instance, Tim, I'd tend to agree with Wiki.