The effects of gunpowder, that great agent in our military activity, were only learnt by experience, and up to this hour experiments are continually in progress in order to investigate them more fully. That an iron ball to which powder has given a velocity of 1000 feet in a second, smashes every living thing which it touches in its course is intelligible in itself; experience is not required to tell us that; but in producing this effect how many hundred circumstances are concerned, some of which can only be learnt by experience! And the physical is not the only effect which we have to study, it is the moral which we are in search of, and that can only be ascertained by experience; and there is no other way of learning and appreciating it but by experience. In the middle ages, when firearms were first invented, their effect, owing to their rude make, was materially but trifling compared to what it now is, but their effect morally was much greater. One must have witnessed the firmness of one of those masses taught and led by Buonaparte, under the heaviest and most unintermittent cannonade, in order to understand what troops, hardened by long practice in the field of danger, can do, when by a career of victory they have reached the noble principle of demanding from themselves their utmost efforts. In pure conception no one would believe it. On the other hand, it is well known that there are troops in the service of European Powers at the present moment who would easily be dispersed by a few cannon shots. But no empirical science, consequently also no theory of the Art of War, can always corroborate its truths by historical proof; it would also be, in some measure, difficult to support experience by single facts. If any means is once found efficacious in War, it is repeated; one nation copies another, the thing becomes the fashion, and in this manner it comes into use, supported by experience, and takes its place in theory, which contents itself with appealing to experience in general in order to show its origin, but not as a verification of its truth. But it is quite otherwise if experience is to be used in order to overthrow some means in use, to confirm what is doubtful, or introduce something new; then particular examples from history must be quoted as proofs. Now, if we consider closely the use of historical proofs, four points of view readily present themselves for the purpose. First, they may be used merely as an _explanation_ of an idea. In every abstract consideration it is very easy to be misunderstood, or not to be intelligible at all: when an author is afraid of this, an exemplification from history serves to throw the light which is wanted on his idea, and to ensure his being intelligible to his reader.