These books and this method of treating naval strategy are valuable beyond measure; but officers find considerable difficulty sometimes in applying the principles set forth to present problems, because of the paucity of data, the remoteness in time and distance of many of the episodes described, and the consequent difficulty of making due allowance for them. Now, no study of naval strategy can be thoroughly satisfactory to a naval officer unless it assists him practically to decide what should be done in order to make the naval forces of his country, including himself, better in whatever will conduce to victory in the next war. Therefore, at the various war colleges, although the student is given books on strategy to study, the major part of the training is given by the applicatory method, an extension of Clerk's, in which the student applies his own skill to solving war problems, makes his own estimate of the situation, solves each problem in his own way (his solution being afterward criticised by the staff), and then takes part in the games in which the solutions presented are tried out. This procedure recognizes the fact that in any human art and science--say medicine, music, or navigation--it is the art and not the science by which one gets results; that the science is merely the foundation on which the art reposes, and that it is by practice of the art and not by knowledge of the science that skill is gained. This does not mean, of course, that we do not need as much knowledge of the science of naval strategy as we can get; for the reason that the naval profession is a growing profession, which necessitates that we keep the application of the principles of its strategy abreast of the improvements of the times, especially in mechanisms; which necessitates, in turn, that we know what those principles are. The applicatory method bears somewhat the same relation to the method of studying books and hearing lectures that exercises in practical navigation bear to the study of the theory. There is one difference, however, as applied to strategy and navigation, which is that the science of navigation is clearly stated in precise rules and formulæ, and the problems in practical navigation are solved by assigning values to quantities like _a, b, c, d_, etc., in the formulæ, and working out the results by mathematics; whereas in strategy, no exact science exists, there are no formulæ, and even the number of assured facts and principles is small. For this reason the art of strategy is more extensive and significant relatively to its science than is the art of navigation to its science.