ADDRESS DELIVERED AT ANNUAL MEETING. 25 thought in the Middle Ages. They did not imitate their master in the study of nature; they contented themselves by studying him. The danger is just as present with us as it was with them ; there is so much to impress, delight, and satisfy us in the marvels of modern science, that perhaps all of us, most certainly the beginner, may easily allow the feeling to get the mastery, that there is nothing left to do, nothing even that needs doing. And then in instructing others (and we all, if we know a little more of anything than those around us, cannot help doing that, even though we may never venture to count ourselves as teachers) it is tempting to human nature to dwell on how much we know, and but slightly on how little we know (which may be the more important of the two) and that is a lesson that finds too apt a pupil in a beginner. It is one of the most hopeful elements in the best teaching of science, that such wise efforts are made to encourage the student to work out problems for himself. It is no easy matter; it is wonderful what pains the average boy will take to avoid think- ing. He will perform the marvellous feat of learning a proposi- tion of Euclid by heart, without understanding it, and he will go through life with two or three adjectives in his vocabulary which he uses with persistent inappropriateness to save himself the terrible trouble of thinking out what he means. But even if we escape from these elementary forms of satis- faction, I am not sure that we have exhausted the dangers. May I try to set before you two habits of mind which are not easy to define, for the words that seem naturally to explain them are themselves of such uncertain meaning (at any rate in common speech) that they need definition before we use them. Idealism and realism, at any rate in their older senses, express the two modes in which one may regard scientific as well as other matters. One may dwell upon the general or on the particular, and I want to urge that the more idealism there is in our thought, the more one seeks for the general, the more progress one can make. It is easy to recognise a proposition of Euclid as true of the particular circles and triangles drawn on the black-board, but it is a distinct sign of progress to prove the pro- position with the figures upside down ; beyond that lies the