the analogous facts of the present; by combining elements taken from reality at different points, we endeavour to form a mental image which shall resemble as nearly as possible that which would have been produced by direct observation of the past event. This is the first operation, inseparable in practice from the reading of the documents. Considering that it will be enough to have indicated its nature here, we have refrained from devoting a special chapter to it.
The facts having been thus imagined, we group them according to schemes of classification devised on the model of a body of facts which we have observed directly, and which we suppose analogous to the body of past facts under consideration. This is the second operation; it is performed by the aid of systematic questions, and its result is to divide the mass of historical facts into homogeneous portions which we afterwards form into groups until the entire history of the past has been systematically arranged according to a general scheme.
When we have arranged in this scheme the facts taken from the documents, there remain gaps whose extent is always considerable, and is enormous for those parts of history in regard to which documents are scanty. We endeavour to fill some of these gaps by reasoning based on the facts which are known. This is (or should be) the third operation; it increases the sum of historical knowledge by an application of logic.
We still possess nothing but a mass of facts placed side by side in a scheme of classification. We have to condense them into formulæ, in order to deduce their general characteristics and their relation to each other. This is the fourth operation; it