The other teaching aspect of this matter is the very significant fact in child psychology that the general development of the child’s mind, like the development of its body, does in fact repeat the history of its ancestors as they passed from gestures and cries to articulate speech and writing and through these from the simplest knowledge to the most complex. The child must therefore, in short, be taken along “the paths upon which in a very real sense every human being has come in person” and the natural method of child teaching must consequently be deduced particularly from a study of the beginnings of speech and writing, books and book collections. In a sense, and in a very real sense, the key to the scientific pedagogy of the future lies in the group of studies summed up as library science, for the library is the late and complex object which sums up in itself the sciences of the book, the word, and all simpler elements of human expression and record, if there be any such. A fourth reason for the study of beginnings is, therefore, that it is the natural method of study and teaching. Finally and closely connected with the preceding reasons is the fact that the purpose of all science is prophecy. We learn not so much that we may teach, as the motto says, but we learn that we may foretell. The object of all science is to understand from what has been the relation of cause and effect in the past, what is likely to be the result of any given set of circumstances in the future. Physics, e.g. has proved a very sure prophetic guide. An engineer can tell with precision that a bridge constructed in a certain way will break if loaded beyond a certain point. Load it to that point and his prophecy becomes true. In the same way, with somewhat less precision perhaps, the biologist can prophesy results in the breeding of plants and animals, the physician can prophesy that quinine will help malaria, the farmer that planted seed under certain conditions will or will not on the average produce certain results, and so on through every branch of human activity. We study in order that we may know the conditions which will be brought about in the future by one or another set of circumstances and so that we may be able to produce the circumstances if we wish the result. The preparation for foretelling may, therefore, be labeled the fifth reason for historical study. § 3. _Definition of the Library_