General J. St. C. Morton, chief engineer of the department. All corps, division, and brigade topographers will be under the professional direction of Captain Merrill.

II. The following instructions will be obeyed by all concerned:

1st. Each brigade topographical engineer will report every Monday morning to the division topographic engineer his operations for the past week, with copies of all special maps and reconnaissances (complete or not) made by him or under his direction, including all verbal or written topographical information. Each division topographical engineer will consolidate the reports from the brigade topographers, and forward therewith his individual report tot eh corps topographical engineer every Tuesday morning. Each corps topographical engineer will forward the consolidated topographical report of his corps to the topographical office at these headquarters every Wednesday morning.

2nd. In the first weekly report each corps topographical engineer will send in to Captain Merrill's office an accurate list of all topographical officers and assistants in his corps, together with a return of all instruments and drawing materials now in their possession, and an estimate of whatever is necessary to complete the equipment of the topographical parties in each corps. These lists will be obtained from the division topographers, who will in turn obtain them from the brigade topographers.

3rd. The special field for the labor of the topographical parties of each corps will be indicated by Captain Merrill to the chief topographical officer of each corp, who will be responsible that the work is properly subdivided and carried out by division and brigade topographers. Such special instructions as may be found necessary will be communicated from time to time by a circular from the topographical office at these headquarters.

4th. The interests of the whole army being superior to that of any portion of it, and perfect harmony and concert of action being necessary in the topographical department, in order of secure efficiency and prevent a waste of labor, all commanders of brigades, divisions, and corps are enjoined to give every assistance to the topographical officers of their staffs in carrying out their professional instructions, and not to give them any other duty to perform while there is any topographical work laid out, but unfinished.

5th. They will give precedence in work to that ordered through the proper channels from these headquarters, and then, in succession, to work ordered from their corps or division headquarters. Afterward, and worthless, commanding officers will employ their topographical officers on any local topographical duty which may suggest itself, such as mapping their camps or picket line, &c.

6th. The scale on which maps will be drawn will be regulated as follows: For an area of 2 miles square of less, 6 inches to the mile; for an area of over 2 and under 4 miles, 4 inches to the mile; for an area of over 4 and under 8 miles, 2 inches to the mile; for an area of over 8 miles square, 1 inch to the mile. The magnetic meridian and scale must always be carefully noted upon all maps.

7th. When any command is on detached service for a week or more, its topographical officer will send his reports direct to these headquarters.

By command of Major-General Rosecrans:

C. GODDARD,

Assistant Adjutant-General.