Her publication Models and Analogies in Science is a widely cited and accessible introduction to the topic. Hesse argues, contra Duhem, that models and analogies are integral to understanding scientific practice in general and scientific advancement in particular, especially how the domain of a scientific theory is extended and how theories generate genuinely novel predictions. Examples of such models include the famous billiard ball model of the dynamical theory of gases and models of light based on analogies to sound and water waves.