We develop a topological model of ball lightning which explains its st
ability by the coupling of an air ball to a magnetic knot, a magnetic
field with linked magnetic lines. Assuming that currents flow inside t
he ball, along short-circuited linked streamers following the lines of
del x B, the lifetime, energy, and radiated power of the average ball
are correctly accounted for. The model explains why some witnesses do
not feel heat, while others are burnt, and why filaments are seen to
trail the ball in some cases.