Early research with liquid helium showed that it had remarkable new properties, especially below the so-called lambda transition near 2.2 K, where there is a sharp, narrow peak in the specific heat (see figure 1(a)). The liquid below the transition was named helium II to distinguish it from the liquid above the transition, called helium I. Three properties discovered in the late 1930s were particularly puzzling. First, a test tube lowered partly into a bath of helium II will gradually fill by means of a thin film of liquid helium that flows without friction up the tube’s outer wall. Second, in the thermomechanical effect, if two containers are connected by a very thin tube that can block any viscous fluid, an increase in temperature in one container will be accompanied by a rise in pressure, as seen by a higher liquid level in that container. Third is the viscosity...

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