Measurements of the polarizability and of the second and third virial coefficients of 4He in the range 4.2 - 27.1 K

New values of the second and third virial coefficients of 4He have recently been reported as a part of work on the gas thermometer scale NPL-75. They are a significant improvement over earlier values as is confirmed by recently completed work on Dielectric Constant Gas Thermometry (DCGT) which is reported briefly here. The experiments also lead to an accurate value for the polarizability of helium, which appears to have a significant difference from theoretical estimates. The details of DCGT will be published elsewhere, but the basic idea is that the procedures of isotherm gas thermometry can be improved by inferring the gas density from measurements of the dielectric constant. (author)