  If a chain is initially at rest in a beaker at a height h1 above the ground,
and the end of the chain is pulled over the rim of the beaker and down towards
the ground and then released, the chain will spontaneously "flow" out of the
beaker under gravity. Furthermore, the beads do not simply drag over the edge
of the beaker but form a fountain reaching a height h2 above it. We show that
the formation of a fountain requires that the beads come into motion not only
by being pulled upwards by the part of the chain immediately above the pile,
but also by being pushed upwards by an anomalous reaction force from the pile
of stationary chain. We propose possible origins for this force, argue that its
magnitude will be proportional to the square of the chain velocity, and predict
and verify experimentally that h2 is proportional to h1.
