ORDERS.] HEADQUARTERS ARMY OF THE POTOMAC, July 29, 1864.

The following instructions are issued for the guidance of all concerned:

1. As soon as it is dark Major-General Burnside, commanding Ninth Corps, will withdraw his two brigades under General White, occupying the intrenchments between the plank and Norfolk roads, and bring them to his front. Care will be taken not to interfere with the troops of the Eighteenth Corps moving into their position in rear of the Ninth Corps. General Burnside will form his troops for assaulting the enemy's works at daylight of the 30th, prepare his parapets and abatis for the passage of the columns, and have the pioneers equipped for work in opening passages for artillery, destroying enemy's abatis, and the intrenching tools distributed for effecting lodgment, &c.

2. Major-General Warren, commanding Fifth Corps, will reduce the number of his troops holding the intrenchments of his front to the minimum, and concentrate all his available force on his right and hold them prepared to support the assault of Major-General Burnside. The preparations in respect to pioneers, intrenching tools, &c., enjoined upon the Ninth Corps will also be made by the Fifth Corps.

3. As soon as it is dark Major-General Ord, commanding Eighteenth Corps, will relieve his troops in the trenches by General Mott's division, of the Second Corps, and form his corps in rear of the Ninth Corps, and be prepared to support the assault of Major-General Burnside.

4. Every preparation will be made for moving forward the field artillery of each corps.

5. At dark Major-General Hancock, commanding Second Corps, will move from Deep Bottom to the rear of the intrenchments now held by the Eighteenth Corps, resume the command of Mott's division, and be prepared at daylight to follow up the assaulting and supporting columns, of for such other operations as may be found necessary.

6. Major-General Sheridan, commanding Cavalry Corps, will proceed at dark from the vicinity of Deep Bottom to Lee's Mill, and at daylight will move with his whole corps, including Wilson's division, against the enemy's troops defending Petersburg on their right, by the roads leading to that town from the southward and westward.

7. Major Duane, acting chief engineer, will have the pontoon trains parked at convenient points in the rear prepared to move. He will see that supplies of sand-bags, gabions, fascines, &c., are in depot near the lines ready for use. He will detail engineer officers for each corps.

8. At 3.30 in the morning of the 30th Major-General Burnside will spring his mine, and his assaulting columns will immediately move rapidly upon the breach, seize the crest in the rear, and effect a lodgment there. He will be followed by Major-General Ord, who will support him on the right, directing his movement to the crest indicated, and by Major-General Warren, who will support him on the left. Upon the explosion of the mine the artillery of all kinds in battery will open upon those points of the enemy's works whose fire covers the ground over which our columns must move, care being taken to avoid impeding the progress of our troops. Special instructions respecting the direction of fire will be issued through the chief of artillery.

9. Corps commanders will report to the commanding general when their preparations are complete, and will advise him of every step in the progress of the operation and of everything important that occurs.