Ten papers deal with the theory of relativity, and all are concerned in some way with electromagnetism. Those who know Whittaker through his Modern Analysis and Analytical Dynamics will recognise in these papers the same mastery over complicated situations which enabled him to disdain the support of notational refinements, that same elegance, brevity and persuasive charm which make difficult arguments seem easier than they really are. The new element which emerges is the strongly geometrical approach; but he remains true to the Lagrange tradition and draws no diagrams of space-time, although these must surely have been before his mind's eye and would have helped his readers.