Summary: In this article Hesse defends the idea that scientific theories are hypothetico-deductive in form. She examines this hypothetico-deductive method by considering some examples from nineteenth-century mathematical physics. By means of these examples she brings out two points about scientific hypothesis. The first is that mathematical formalisms, when used as hypotheses in the description of physical phenomena, may function like the mechanical models of an earlier stage in physics, without having in themselves any mechanical or other physical interpret. The second point is that most physicists do not regard models as literal descriptions of nature, but as standing in a relation of analogy to nature.
Comment: A really good paper about models in science, mathematical formalism and hypothesis. Highly recomended for postgraduates studying philosophy of physics, although it could also be readable by undergraduates (last years) with previous knowledge of scientific modelling.