Helium Temperatures from Vapor Pressure Measurements

Abstract

It is found that the temperature at any point below the surface of a helium bath, as deduced from pressure measurements over the surface corrected for hydrostatic head, does not agree with the temperature obtained using a vapor pressure bulb, the helium bath pressure invariably indicating a lower temperature, except below the λ point. The discrepancy can be reduced but not eliminated by employing a heater at the bottom of the bath to provide a copious supply of vapor bubbles throughout the bath. A sharp temperature gradient at the surface of the bath is indicated. Below the λ point no discrepancy is observed.