The surface tension, (sigma), of a liquid approaches zero as (T ightarrow T_{c}) from below. Define

The surface tension, \(\sigma\), of a liquid approaches zero as \(T \rightarrow T_{c}\) from below. Define an exponent \(\mu\) by writing

\[
\sigma \sim|t|^{\mu} \quad(t \lesssim 0) .
\]

Identifying \(\sigma\) with the "free energy associated with a unit area of the liquid-vapor interface," argue that \(\mu=(d-1) v=(2-\alpha)(d-1) / d\).

[Note: Analysis of the experimental data on surface tension yields: \(\mu=1.27 \pm 0.02\), which agrees with the fact that for most fluids \(\alpha \simeq 0.1\).]