## Abstract

The two isotopes of helium offer unique opportunities to test fundamental theories of quantum fluids. In liquid <latex>$^4$</latex>He, a Bose liquid, the elementary excitations have been studied extensively over the last two decades by neutron inelastic scattering. Similar studies of liquid <latex>$^3$</latex>He, the Fermi liquid counterpart of liquid <latex>$^4$</latex>He, have become possible only recently. From the results obtained so far for normal liquid <latex>$^3$</latex>He, the existence of zero sound as a well defined density excitation at finite wavevectors (q <latex>$\approx$</latex> q<latex>$_F$</latex>) and finite temperatures (T <latex>$\approx$</latex> T<latex>$_F$</latex>) has been verified and the spin fluctuation spectrum has been measured. By comparing the neutron scattering results for the density fluctuation spectrum with R.P.A. calculations with generalized polarization potentials, important information has been obtained about the effective spin-symmetric interaction between <latex>$^3$</latex>He atoms. The spin fluctuation spectrum is in agreement with the paramagnon model if a value close to unity is assumed for the contact dimension-less paramagnon parameter I. This implies that the nuclear spin system in normal liquid <latex>$^3$</latex>Hc is close to ferromagnetic.