He made researches into the subjects of lake dwellings, primeval pottery, and burial urns. One of his most valuable writings was upon the subject, "Was the Roman Army provided with Medical Officers?" He answered the question in the affirmative after a laborious hunt amongst votive and mortuary tablets; no Roman historians had left clear indications of the existence of any army medical department. He found that several tablets were preserved bearing inscriptions referring to army surgeons, which suggested that although they were all known as _medicus_ there were degrees of rank amongst them, notably the _medicus legionis_ and the _medicus cohortis_. There is a well-preserved tablet in the Newcastle Museum found in that neighbourhood, commemorating a surgeon of the first Tungrian cohort, and one in Dresden, referring to a _medicus duplicatorius_, a term which indicates that the surgeon had been fortunate enough by his attainments to merit, and, we hope, receive double fees for his services. All his antiquarian study was looked upon by Simpson himself as no more than a relaxation. Fatigued by days and nights of anxious consecutive professional work, he would suddenly dash off for a day into some part of the country where he knew there was a likely "find," leaving patients and students to the care of his assistants. Here he would press into service and infect with his spirit all sorts of local worthies from the squire or laird down to the labourer, who woke up at his stimulation to find that what had been of no concern to them and their fathers before them--perhaps objects of vituperation or superstitious dread--were objects of keen delight and interest, and actually valuable to this astonishing man. Once on a professional visit to Fifeshire he quite casually discovered some remarkable though rough carvings in caves, representing various animals and curious emblems, and he was able to show that they presented features hitherto unnoticed. Fifeshire was famous for its underground dwellings, or, as they are locally called, "weems"--a term which gave origin to the title of the Earldom of Wemyss. After such an excursion he would return to Queen Street full of boyish spirits, eager to narrate his discoveries to interested friends, and refreshed ready to resume the daily round of work. Archaeology was his hobby--the hobby on which he rode away for refreshment and relief from the monotony of his life's work; not only did the hobby constantly restore his flagging energies, but as it is given to few men to do, he put new life into his hobby whenever he bestrode it. In the conduct of his practice he was somewhat negligent. He was one of the old school in these matters; he trusted his head rather than paper, and his head had had such a careful self-imposed training since childhood that it was a good servant. But where the brain has such enormous duties to perform, those which appear to it unimportant must of necessity be comparatively neglected.