 It might appear that the success of the kinetic theory marked a successful instantiation of the kind of atomism aspired to by the mechanical or Newtonian atomists, since macroscopic phenomena are explained in terms of atoms with just a few specified mechanical properties. There are reasons to resist such a view. Firstly, neither the molecules of the kinetic theory nor the atoms composing them were ultimate particles. As we have noted, it was well appreciated that they needed an inner structure to accommodate spectra. Secondly, it was well apparent that the mechanical properties attributed to molecules by the kinetic theory could not constitute an exhaustive list of those properties. Further properties were required to explain cohesion and chemical interaction for instance. Thirdly, and perhaps most fundamentally, the kinetic theory was not an attempt to give an atomic account of the ultimate structure of matter. Maxwell, for one, was quite clear of the distinction between an atomism that made claims about the ultimate structure of matter for some very general metaphysical reasons, on the one hand, and a specific scientific theory postulating atoms on the other (Niven, 1965, Vol. 2, 361–4). The kinetic theory was an example of the latter insofar as it was proposed, not as an ultimate theory, nor as a theory of matter in general, but as a theory designed to explain a specified range of phenomena, in this case the macroscopic behaviour of gases and, to a less detailed extent, of liquids and gases too. As such, it was to be judged by the extent it was able to fulfil that task and rejected or modified to the extent that it could not. A case for the existence of atoms or molecules and for the properties to be attributed to them was to be sought in experimental science rather than philosophy.