A nation can hardly achieve military success without paying special heed to its _material_ of war. It is the explicit duty of a nation's constituted guardians assiduously to apply all the resources of science and art, of theory and practice, of experience and invention, of judgment and genius, to the systematic production of the best military apparatus. Ordnance and ordnance stores, arms and equipments, commissary and quartermaster supplies, the means of transportation, fortifications and engineer-trains, navies and naval appliances,--these are the material elements of military strength, which decide the fate of nations. If in these we are behind the age, our delinquency must be atoned by disaster and wasted lives. Civilization conquers barbarism chiefly by its superior skill in the construction and use of the material instruments of warfare. Courage and conduct are certainly important factors in all legitimate successes; but they must work through material means, and are emphasized or nullified by the skill or rudeness exhibited in the device and fabrication of those means. The great contest now in progress has taught us afresh the potency of those material agencies through which patriotic zeal must act, and we shall hereafter lack all good excuse for _not_ having the very best attainable system of producing, preserving, providing, and using whatever implements, supplies, and muniments our future may demand. As an aid in this direction, we welcome the truly valuable book which General Cullum has now supplied on one of the Special brandies of military _materiel_. We owe him thanks for his treatise on military bridges, which was nearly as much needed as though we had not already the works of Sir Howard Douglas, Drien, Haillot, and Meurdra, and the chapters on bridges by Laisne and Duane. General Cullum's work has more precision and is more available for practical guidance than any other. The absolute thoroughness with which the India-rubber pontoon system is described by him gives a basis for appreciating the other systems described in outline.