We have pointed out as an absurdity the idea of a strategic reserve which is not to co-operate in the capital result, and as it is so beyond a doubt, we should not have been led into such an analysis as we have made in these two chapters, were it not that, in the disguise of other ideas, it looks like something better, and frequently makes its appearance. One person sees in it the acme of strategic sagacity and foresight; another rejects it, and with it the idea of any reserve, consequently even of a tactical one. This confusion of ideas is transferred to real life, and if we would see a memorable instance of it we have only to call to mind that Prussia in 1806 left a reserve of 20,000 men cantoned in the Mark, under Prince Eugene of Wurtemberg, which could not possibly reach the Saale in time to be of any use, and that another force Of 25,000 men belonging to this power remained in East and South Prussia, destined only to be put on a war-footing afterwards as a reserve. After these examples we cannot be accused of having been fighting with windmills. CHAPTER XIV. Economy of Forces The road of reason, as we have said, seldom allows itself to be reduced to a mathematical line by principles and opinions. There remains always a certain margin. But it is the same in all the practical arts of life. For the lines of beauty there are no abscissae and ordinates; circles and ellipses are not described by means of their algebraical formulae. The actor in War therefore soon finds he must trust himself to the delicate tact of judgment which, founded on natural quickness of perception, and educated by reflection, almost unconsciously seizes upon the right; he soon finds that at one time he must simplify the law (by reducing it) to some prominent characteristic points which form his rules; that at another the adopted method must become the staff on which he leans. As one of these simplified characteristic points as a mental appliance, we look upon the principle of watching continually over the co-operation of all forces, or in other words, of keeping constantly in view that no part of them should ever be idle. Whoever has forces where the enemy does not give them sufficient employment, whoever has part of his forces on the march—that is, allows them to lie dead—while the enemy’s are fighting, he is a bad manager of his forces. In this sense there is a waste of forces, which is even worse than their employment to no purpose. If there must be action, then the first point is that all parts act, because the most purposeless activity still keeps employed and destroys a portion of the enemy’s force, whilst troops completely inactive are for the moment quite neutralised. Unmistakably this idea is bound up with the principles contained in the last three chapters, it is the same truth, but seen from a somewhat more comprehensive point of view and condensed into a single conception. CHAPTER XV. Geometrical Element