Realise, secondly, that _you have the materials and the opportunity of psychological observation always with you_. Truly, we must have laboratories; if we are to attain to accurate and comparable results, we must put ourselves under conditions that can be rigorously controlled. But get the habit of psychological observation, and you will be surprised to find (though it follows, does it not, from the laws of attention?) how much psychology there is in your daily life; how often you can snapshot a baffling experience, and catch a hint of analytical possibilities; how often you light upon something that the text-books do not discuss, but that this habit of observation reveals and places for you. Take the occasions as they come; plenty of good astronomical work has been done with a pair of opera glasses!—and if you cannot, later on, experiment for yourself in a laboratory, at least you have gained a new outlook and a new competence; it is as if you had gained access to a whole literature by the mastery of some foreign language. Realise, thirdly, that _a system of science, whether the science be psychology or any other, is built up of nothing else than facts and logic_. The facts of observation are the essential things; without them there is no science possible; but logic makes the facts available and rememberable; it groups and classifies, decides the sequence of chapters and paragraphs, points to gaps and discrepancies in the record of facts, governs the whole presentation. So there should be nothing more in a text-book of science than facts and logic. The man of science, trying to answer an unanswered question (p. 277), will guess and forecast and speculate and imagine; and some of his guesses and speculations may be worthy of mention in the history of his science; but there should be no glimmer of them in the scientific system. Science, you remember, is impersonal and disinterested, dry fact and cold logic; there are all sorts of personal adventures and interesting episodes by the way, while science is in the making; but if you have the scientific temperament, you feel the fascination of fact and logic themselves.