ADVANCES IN THE INVESTIGATION OF THE NEMATIC-SMECTIC A TRANSITION : MAGNETIC STUDY OF MIXTURES OF MESOMORPHIC COMPOUNDS M. F. ACHARD, H. GASPAROUX, F. HARDOUIN et G. SIGAUD J. Phys. Colloques, 37 C3 (1976) C3-107-C3-112 DOI: 10.1051/jphyscol:1976318