Abstract
The birefringence has been measured for the homologous series of N-(4-n-pentyloxybenzylidene)-4-n-alkylaniline (50.m) where m = 4 ∼ 8. An odd-even alternation of jumps in the birefringence at the nematic-smectic A transition temperatures is exhibited for the homologous series. The nematic-smectic A transitions are confirmed from the jumps to be of first-, second-, first-, very weakly first-, first-order, in going from 50.4 to 50.8. The transition order of these compounds is discussed in terms of the critical exponent of a Landau mean-field model.