HDQRS. NORTHERN DISTRICT, DEPT. OF THE SOUTH, Morris Island, S. C., September 2, 1864.

CAPTAIN: I have the honor to report that nothing of special interest has occurred within this district since my last communication.

On the 28th ultimo, 2 deserters from the Forty-seventh Georgia Infantry came into our lines, having crossed the marsh and swam the creeks from Secessionville to Long Island. A report of their examination is forwarded by the provost-marshal of the district. They bring no general news of any interest and represent the enemy's forces about Charleston very nearly the same as last reported by me. Their own regiment, the Forty-seventh Georgia, they state, has now only about 250 men for duty, a very large number being sick in hospital. They do not consider that any offensive operations are intended,and the fact that volunteers, were called for to se Secessionville on fire certainly indicates considerable timidity on the part of the enemy.

Parties of the enemy have shown themselves of late more frequently than usual in front of Long and Cole's Islands, but have not as yet taken the offensive. The fatigue duty is continued as before on the works along their entire line. On the 26th ultimo, a party commanded by Captain Friedle, Fifth-fourth New York Volunteers, landed at Legareville. They explored the country for over a mile from the river, but found no signs of batteries nor any force of the enemy. The party returned at evening, after having knocked down the chimneys which impeded our view.

On the night of the 28th ultimo, a pontoon-boat, fitted up for the purpose and containing about twenty hundredweight of powder, was taken out by Lieutenant G. F. Eaton, One hundred and twenty-seventh New York Volunteers, boat infantry, and floated down into the left flank of Fort Sumter. The garrison of Sumter was alarmed before the mine reached them, and opened upon our boats with musketry, without, however, doing them any injury. Owing to the fact of the officers of the boat infantry having miscalculated the rate of the current, especially near the fort, where threw seems to be nearly dead water, the mine exploded about 50 yards from the fort and did not apparently do it any injury. On the night of the 31st ultimo six torpedoes, made of barrels set in frames, each containing 100 pounds of powder, were set afloat with the flood-tide from the southeast of Sumter with the view of destroying the boom. They probably exploded too early and only injured perhaps two lengths or links of the boom, which are not now visible.

The firing form our front battery since my last report (nine days) has been as follows: At Fort Sumter, 936 shells; at the city, 298 shells. The enemy has fired during the same time from his batteries on James and Sullivan's Islands 490 shells, which have been duly responded to from Fort Strong. The enemy has thrown mortar shells at Paine's Dock for several nights past.

I have made the following alterations in the armaments of some of my smaller batteries: From Long Island I have taken away two 30-pounder Parrotts and placed there one of the 12-pounder howitzers captured from the enemy on James Island last July. From the battery on the right of Cole's Island, I have removed one 10-inch columbiad and two 10-inch mortars, leaving there two 30-pounder Parrotts, and one captured 12-pounder. In the battery on the left of Cole's Island I have placed two 10-inch columbiads. In the oystershell fort on Cole's Island I have placed two 30-pounder Parrotts.