The work of Arthur Dempster generally has been considered significant but of less importance in the growth of mass spectrometry than that of Francis Aston, and as essentially limited to the pre‐WW II era. The development of mass spectrometry, however, as distinct from nuclear science, was shaped far more by Dempster than by Aston. This influence is seen in several aspects of instrument design and practice, and it has continued into the 21st century.