  If we take atomism to involve the claim that the properties of macroscopic matter arise as a result of the combinations and motions of tiny particles, then it is a position confirmed by the time of the Solvay Conference in 1911 in a way that left little room for sensible doubt. But if we take atomism in a stronger sense, to mean a theory that explains all of the properties of macroscopic matter in terms of underlying particles with specified properties and governed by specified laws, then it must be denied that atomism had reached its objective in 1911. There were identifiable inadequacies and gaps in the specification of the properties of atoms and the electrons and protons that compose them and there were to an increasing extent problematic experimental results that were eventually to lead to a radical change in the laws that were presumed to govern the behaviour of atomic and sub-atomic particles.