ABSTRACT
George Freidel conducted many experiments on LCs in the beginning of the 20th century, and he was the rst to explain the orienting effect of electric elds and the presence of defects in LCs. In 1922 he proposed a classi cation of LCs based upon the different molecular orderings of each substance. Between 1922 and World War II Oseen and Zöcher developed a mathematical basis for the study of LCs.
