"Part of the value of his work is due to the exceptional opportunities which he enjoyed. When the war of 1806 began he had long been the personal adjutant of one of the Prussian princes, and an intimate friend of Scharnhorst, who was probably the greatest of Napoleon's contemporaries. In the period of reorganization which followed the Peace of Tilsit he made the acquaintance of Gneisenau, and of almost all the officers who made their mark in the subsequent wars of liberation. During the years of preparation he was Scharnhorst's assistant, first in the Ministry of War and then on the General Staff. During the campaign of 1812 he served with the Russian army as a staff officer. Thus his experience during the four years of the Wars of Liberation was that of one who was continually behind the scenes, always in touch with the Governments and Generals, and therefore better able than any one not so favourably placed to see everything in its proper perspective, and to follow and appreciate the considerations which directed the decisions both of statesmen and of the commanders of armies. His personal character was of the finest mould, and his writings have the sincerity, the absence of which makes it so difficult to rely upon those of Napoleon. "The ultimate test of the value of books is time. When Clausewitz died, the two books on war which were thought the best were those of the Archduke Charles of Austria and General Jomini. To-day the book of Clausewitz, 'On War,' easily holds the first place. It is the least technical of all the great books on war; from beginning to end it is nothing but common sense applied to the subject, but for that reason it is the hardest to digest, because common sense or a man's natural instinctive judgment on any subject is exceedingly hard to analyse and put into words. An exceptionally gifted man can go through this process, but few can follow it for any length of time without a distinct effort.