This essay discusses the historical and scientific basis of the two theories of the nucleus which led to the groundbreaking 1938 theory of nuclear fission by Lise Meitner and Otto Frisch. The first theory, developed between 1928 and 1936, was pioneered by George Gamow, who suggested that the nucleus could be considered to be like a drop of liquid, with energy holding the subatomic particles together just as tension holds together liquid particles. The second theory is Niels Bohr’s 1936 theory of the compound nucleus, which describes the way in which particles may be released from the nucleus or that the nucleus may be destroyed by raising the energy of a particle which strikes the nucleus. The author suggests that Meitner and Frisch combined those two theories reach a theory of fission that describes how a nucleus may be split and the energy that is produced. Although the article does present the equations and the reasoning behind the theories, it is largely understandable by a general audience.