Did Perrin’s experiments convert Poincaré to scientific realism?

In this article, I argue that Poincaré’s acceptance of the atom does not indicate a shift from instrumentalism to scientific realism. I examine the implications of Poincaré’s acceptance of the existence of the atom for our current understanding of his philosophy of science. Specifically, how can we understand Poincaré’s acceptance of the atom in structural realist terms? From a careful examination of his 1912 paper, I suggest that it does not entail scientific realism in the sense of acceptance of the fundamental existence of atoms but, rather, argues against fundamental entities. I argue that Poincaré’s paper motivates a nonfundamentalist view about the world and that this is compatible with his structuralism