From the important character of these duties as connected with the means essential to a national defence, and the vast amount of money expended in these operations, it is evident that a high order of acquirements should be deemed necessary to qualify one to perform the duties of a military engineer. This officer requires a knowledge of chemistry, to guide his choice of materials for mortars, cements, and mastics; of mineralogy and geology, for selecting stone; of botany, for timber and the means of preventing its decay; of mathematics, in laying out his work and calculating the thickness and stability of his walls, embankments, &c.; of mechanical philosophy, in constructing his machinery; of military engineering, in his plans of fortifications; and of all the higher branches of military science, in selecting positions for these works, such that they shall have the proper relations to the means of national defence, and to the grand operations of armies in the field. The avenues to appointment to this corps are guarded, in most European armies, with special care, to prevent the influence of money, politics, or family connections; and in our own army it is now specified by law of Congress, that the vacancies shall be filled only from the most distinguished graduates of the military academy. Formerly our service suffered most severely from the employment of incompetent persons, introduced through political influence from civil life, and foreign charlatans, the refuse of European armies. Many of our earlier military works (as will be mentioned hereafter) were modelled upon systems for a long time discarded by the profession in Europe, and even some of those which have been constructed within the last thirty years are made of such wretched materials and workmanship, that they are already crumbling into ruins. While the existing laws and regulations seem well calculated to prevent the recurrence of similar abuses and errors, it nevertheless can be shown that the organization of this arm of our service requires modifications and extensions to give it the requisite degree of efficiency, and to economize the public expenditures.