We have applied a recently developed method for sensitive calorimetric measurements to investigate the nematic—smectic-$A$ phase transition in pure N-$p$-cyanobenzylidene-$p-n$-octyloxyaniline. The results indicate a very weak first-order transition with a transition entropy of $(0.017\mathrm{}\pm 0.002)R_0$. The critical exponents of the specific-heat anomaly have nonclassical values $\alpha =0.16\mathrm{}\pm 0.01$ and ${\alpha }^{\prime }=0.14\mathrm{}\pm 0.02$.

• Received 13 June 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.1126