Superfluid helium, a state of matter existing at low temperatures, shows many remarkable properties.
One example is the so called fountain effect, where a heater can produce a jet of helium. This
converts heat into mechanical motion; a machine with no moving parts, but working only below 2 K.
Allen and Jones first demonstrated the effect in 1938, but their work was basically qualitative. We
now present data of a quantitative version of the experiment. We have measured the heat supplied,
the temperature and the height of the jet produced. We also develop equations, based on the
two-fluid model of superfluid helium, that give a satisfactory fit to the data. The experiment has
been performed by advanced undergraduate students in our home institution, and illustrates in a
vivid way some of the striking properties of the superfluid state.