The _chief of staff_ is a recent French imitation. The first officer assigned in that capacity was General Marcy, on the staff of General McClellan, in the fall of 1861. Previous to that time the officers of the adjutant-general's department--on account of their intimate relations with commanding officers, as their official organs and the mediums through which all orders were transmitted--had occupied it. The duties of these officers, however, being chiefly of a bureau character, allowing them little opportunity for active external supervision, it has been deemed necessary to select for heads of the staffs, officers particularly qualified to assist the commander in devising strategical plans, organizing, and moving troops, etc.; competent to oversee and direct the proceedings of the various staff departments; untrammelled with any exclusive routine of duty, and able in any emergency, when the commander may be absent, to give necessary orders. For these reasons, although the innovation has not been sanctioned by any law, or any standing rule of the War Department, and although its propriety is discussed by many, the custom of assigning officers as chiefs of staff has become universal, and will probably be permanent. The extent and character of their duties depend, however, upon themselves, being regulated by no orders, and the high responsibilities attached to the position in France have not thus far been assumed by the officers occupying it here. In the French service, the chief of staff is the actual as well as the nominal head of the organization; he supervises all its operations; he is the _alter ego_ of the commander. In the Waterloo campaign, for instance, Marshal Soult was the chief of Napoleon's staff, and the emperor attributed his disaster, in part, to some of the orders issued by the marshal. Our limits will not permit a description of the duties pertaining to the various members of the staff, but we pass to the consideration of those departments, the operations of which most directly affect the soldier, are indispensable to every army, and are most interesting to the public.