It is by no means easy for the applied mathematician to decide how much importance he should attach to the more abstract and aesthetic side of his work and how much to the detailed applications to physics, astronomy, engineering or the design of instruments. To all appearances, Sir William Rowan Hamilton (1850-1865) attached little importance to the practical applications of his method, and it was only with the publication of his Mathematical Papers that it was possible to form a more correct and balanced judgement of Hamilton as an applied mathematician. Great indeed was the labour which he employed with a view to applying his method to the design of optical instruments, but for him the abstract wand aesthetic side of his work was of so much greater public importance than its practical use that the details of application remained unpublished till long after her death and long after other workers had discovered equivalent processes.