Measurements of the adsorption and desorption of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ on the porous polycarbonate substrate Nuclepore are reported for nominal pore diameters of 30, 50, 80, and 200 nm. The isotherms are measured directly by a newly developed capacitance technique. The theory of Saam and Cole, relevant to capillary condensation in cylindrical pores, is examined and confirmed by the data. Pore distributions for the several Nuclepore samples are determined by two techniques.

• Received 16 July 1987

DOI:https://doi.org/10.1103/PhysRevB.36.8294