On the Depression of the Superfluid Transition Temperature inHe4by a Heat Current

We have attempted to measure the depression of the superfluid transition temperature $T_{\lambda }$ in liquid helium by a heat current $Q$, and found that within our precision, $T_{\lambda }$ is independent of $Q$ for $0.2\le Q\le 2$ ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$. An effect of the size $\frac{\Delta T_{\lambda }}{Q}\cong 3\times {10}^{-3\mathrm{}}$ K ${\mathrm{cm}}^2$/W would have been observable. This upper limit is inconsistent with the value 59 × ${10}^{-3\mathrm{}}$ K ${\mathrm{cm}}^2$/W reported recently by Bhagat and Lasken for ${10}^{-3\mathrm{}}\le Q\le {10}^{-1\mathrm{}}$ ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$.