Simpson's method of study was simple, at the same time that it involved immense labour. In entering upon a new work his first proceeding was to ascertain conscientiously all that had already been said or written by others upon the subject. He traced knowledge from its earliest sources and was able, as he followed the mental workings of those who had preceded him, to estimate the value of every vaunted addition to the sum of knowledge; and to weigh the theories and new opinions of men which had been evolved with the progress of time, and which had sometimes obscured, instead of casting greater light upon the truth. His antiquarian tastes added to his knowledge of Latin helped him in this work and turned a tedious task into a real pleasure. This preliminary accomplished, he plunged into the work of adding to the knowledge of the subject by thought, research, experiment, or invention. In writing upon an abstract subject he would disentangle the confused thoughts of his predecessors and restate their opinions in direct and simplified language. But matters of opinion never had such an attraction for him as matters of fact; in dealing with these latter he would test by experiment the statements of authorities and correct or add to them by his own researches. Most of his professional writings, as well as his archaeological works, are valuable for the historical _resume_ of the knowledge on the subject as well as for his additions. His later writings show as careful an attention to the inductive method with which he started, as those produced in the days of his more youthful enthusiasm; when fame was attained and fortune secured, when excessive work was sapping his physical strength, he never sank into lazy or slovenly methods in scientific work, but ever threw his whole vigour into the self-imposed task. When studying Nature directly he was constantly asking her "why?"--just as in his notes of his teacher's lectures the query was ever recurring. He never felt himself beaten by an initial failure, but returned again and again with his questions with renewed energy each time. He was not to be denied, and in this manner he wrested from Nature some of those precious secrets the knowledge of which has relieved suffering and prolonged human life in every corner of the globe. "He never kept anything secret," says his nephew and successor, Professor A. R. Simpson, "that he thought could help his fellows, and it is hard to say whether his delight was greater in finding some new means to cure disease, or in demonstrating to others his methods of treatment."