PRESSURE-VOLUME ISOTHERMS OF He$sup 3$ BETWEEN 1.5 AND 3.8 K

$\mathrm{PV}$ isotherms of ${\mathrm{He}}^{3}$ gas have been measured at 3.786, 2.991, 2.161, 1.818, and 1.516\ifmmode^\circ\else\textdegree\fi{}K. Values of the second virial coefficient, $B$, derived from the data, are, respectively, -65.37, -86.25, -117.9, -142.3, and -168.0 cc/mole. For only the isotherms of 3.786 and 2.991\ifmmode^\circ\else\textdegree\fi{}K was the third virial coefficient found to be significant. These values are 1132 and 1718 ${\mathrm{cc}}^{2}$/${\mathrm{mole}}^{2}$, respectively. The measured $B'\mathrm{s}$ are shown to be in satisfactory agreement with those calculated using a modified Slater-Kirkwood type potential, with constants chosen to give a good fit to the measured ${\mathrm{He}}^{4}$ $B'\mathrm{s}$ below 4\ifmmode^\circ\else\textdegree\fi{}K.