A comparison of the dielectric-constant-enhancement theory of Leroux Hugon and Ghazali with previous experimental data shows their calculated $N_c$ nearly a factor of 3 too small, thus giving less than satisfactory agreement with experiment. Questions about the adequacy of their theoretical approach are also discussed.

• Received 24 October 1978

DOI:https://doi.org/10.1103/PhysRevB.20.3505