Abstract: | We report measurements of the local density response inside a quasi 1-D horizontal3He fluid layer to a step-like change T of the boundary temperature, where |T| 80 K and much smaller than |T – Tc| where Tcis the critical temperature. These experiments used a new cell design, described in the text, and were carried out along the critical isochore both above and below Tc. The observed temporal and spatial density response (t, z) and its equilibration time are described adequately by the relations developed from the thermodynamic theory of Onuki and Ferrell. We verify that over the temperature range of low stratification, where computer simulations and closed-form calculations can be compared, they are in exact agreement. The systematic differences of experimental results from predictions can be accounted for by the departure of the cell from the ideal 1-D geometry. The much larger disagreement between the experimental and predicted equilibration time scale in earlier experiments is also explained. Finally, deviations from linearity observed in the density response for steps |T| larger than 90 K are reported and the implications of such nonlinearity for the (t, z) profile and especially the effective relaxation time effare analyzed. We also discuss the predicted onset of convection near Tcfor the conditions in our experiment. In the Appendix, the likely sources for systematic deviations in the density response function for the experimental cell from calculations in the ideal 1-D geometry are presented and their effects calculated. The so-obtained response function ZF(, z) is compared with previously published data. |