AEPINUS, Franz Maria Ulrich Theodor, a distinguished German natural philosopher, was born at Rostock in Saxony in 1724, and died at Dorpat in August 1802. He was descended from John Aepinus (ό. 1499— d. 1553), the first to adopt the Greek form (αίπϵvός) of the family name, a leading theologian and controversialist at the time of the Reformation. After studying medicine for a time, Francis Aepinus devoted himself to the physical and mathematical sciences, in which he soon gained such distinction that he was admitted a member of the Berlin Academy of Sciences. In 1757 he settled in St Petersburg as member of the Imperial Academy of Sciences and professor of physics, labouring there and pursuing his favourite studies with great success till his death. He enjoyed the special favour of the Empress Catharine II., who appointed him tutor to her son Paul, and endeavoured, without success, to establish normal schools throughout the empire under his direction. Aepinus is best known by his researches, theoretical and experimental, in electricity and magnetism. His principal work, Tentamen Theoriae Electricitatis et Magnetismi, published at St Petersburg in 1759, may be regarded as the first systematic and successful attempt to apply mathematical reasoning to these subjects. Adopting Franklin’s theory of positive and negative electricities, or electric forces, he investigated the relations of these fully, and especially the conditions of their equilibrium; and many of the conclusions he arrived at do not depend for their value and importance on the theory of Franklin. Aepinus himself extended the theory, holding that the particles of the electric fluid repel each other, attract the particles of all bodies, and are attracted by them, with a force inversely proportional to ...