To carry out this mutual co-operation of practical work and the study of old examples, I would recommend you always to note down any puzzle you fall into in your work, and any doubt as to how a perplexity is to be met or difficulty to be got over, and any uncertainty which may occur to you as to the best mode of treating a particular feature; so that, when you next go out sketching, you may have a list of questions for which you have to seek for practical answers from the old architects themselves, still speaking to us and instructing us through their works; and in the same way you may have, ever and anon, answers suggested by the old men to questions which you have not yet thought of asking, but which in your practical work you will soon find to arise. This playing of practice and study into each other’s hands will add vastly to the pleasure and profit of both, and will keep up a zealous and lively interest in your minds which will make your return to business only second in enjoyment to your setting out on a sketching tour; the one keeping alive by practical use the pleasure and interest of the lessons learned by the other. I must now say a word, which perhaps ought to have come at the beginning of my last lecture, about preparation of another kind for this class of study. I need hardly dwell upon the obvious necessity for having acquired at the outset, and for constantly continuing to acquire, a knowledge _from books_ of the subject you are studying. At the beginning of this century it was wholly unknown; since that time it has gradually become better and better understood; and it is clear that, to carry on this cumulative process, each generation of students must take as their basis the full amount of knowledge yet attained, and--riding as it were on the crest of the wave--must add their own progress to that attained by their predecessors. I will not attempt to enumerate books. If you are anxious to follow up the subject, you will already have found them out or will soon do so. I will mention, however, that you must not limit your reading to _English_ works, for the French have done, I think, even more than our own countrymen to elucidate the subject; and among English writers let Professor Willis take a leading place as your instructor. But what you have to learn from books is not architecture alone. I will not stop to insist on the necessity of general reading, just as every one should follow up: some of the usual classes of general reading are, however (if it were possible) even more directly important in their minute details to architects than to others: I would more especially instance _historical_ knowledge, and all that tends to illustrate the changes which have influenced civilisation, and through it have borne more or less directly upon art.