 Independent studies of the ontology of chemistry on the basis of mereology have been undertaken by several authors (Earley 2005, Harré and Llored 2011, Needham 2010a). In disputing Scerri’s (2000, 2001) argument against claims (Zuo et al. 1999) that orbitals have been observed, Mulder (2010) appeals to a general ontological distinction between entities, which can appropriately be said to exist, and states which don’t exist independently but are features of entities that exist. Ostrovsky (2005) and Schwarz (2006) take issue with the role of approximations in Scerri’s argument.