  Stereo-chemistry emerged as a result of taking the structures depicted in chemical formulae of substances to be indicative of actual structures in the molecules of those substances. Pairs of substances that had crystal structures that were mirror images of each other but which were otherwise chemically identical were represented by formulae that were themselves mirror images of each other. Optical rotation gave independent evidence for the reality of these underlying structures.  Some chemists were reluctant to assert that the structures were in fact depictions of the physical arrangements of atoms in space, a stand supported by the fact that there was still no theory that connected physical arrangements of atoms with physical and chemical properties.  There were eminent scientists, notably Ostwald (1904) and Duhem (2002), who, whilst accepting that the phenomena were indicative of some underlying structure, refused to make the further assumption that the formulae with their structures referred to arrangements of atoms at all. Two factors provide a rationale for their stance. Firstly, the use of formulae in chemistry could be accepted without committing to atomism, as we have discussed above, and as both Ostwald and Duhem stressed. Secondly, an analogy with electromagnetism indicates that structural features need not be indicative of underlying physical arrangements accounting for those structures. The electric field has the symmetry of an arrow and the magnetic field the symmetry of a spinning disc, but there is no known underlying physical mechanism that accounts for these symmetries. Stereo-chemistry may not have provided a case for atomism that was logically compelling, but it certainly enabled that case to be strengthened.