Saturday, August 22.-No attempt to advance the sap was made to-day. The sappers and an infantry detail were employed in strengthening the fourth parallel, widening trench, and building banquette tread and loop-holes for sharpshooters.

To-day I reported in writing to the general commanding the facts above recorded, relating to the progress of the sap for the past twenty-four hours; also that--

One Requa battery* was mounted last night on the right of the first line of approach to the rear of the fourth parallel, so placed as to enfilade its face and the beach. Another battery of this kind is about 50 yards in rear of the fourth parallel, near the center of the island, and taking this parallel in reverse. Two other Requa batteries are in the third parallel. These four light defensive pieces comprise all the artillery in position in advance of the second parallel.

I think it will be impossible to continue the sap in the daytime under Wagner's artillery fire. But if our picket line continues to advance, which can only be done with considerable loss, we may make some progress each night. Should the enemy's pickets retire inside his work, which they will soon be forced to do, he will then maintain an artillery fire from his light guns in the fort, which will make it impossible for the sap to progress night or day until this fire be subdued or kept down. His light guns are now run behind the merlons of the work to avoid our shot; hence it is only by destroying the parapet of the fort with our heavy guns in the second parallel, thus uncovering them, or by rendering their service impossible by a superior fire from light pieces which can be mounted in the fourth parallel, assisted by a strong force of sharpshooters, that we can proceed with certainty. (Our light guns in the second parallel cannot be used effectively against Wagner, on account of the distance, and the fact that their endangers our own men in the advanced works; five, I am informed, have already been injured.) Destroying the parapets I consider the best plan, for, so long as the enemy is so strongly entrenched in Wagner, he will give us serious annoyance, and possess an excellent base from which to assault our works, which he must more than ever be convinced is his only hope.

The general commanding expressed himself unwilling to risk a battery of light guns in the fourth parallel, and not yet ready to spare any considerable amount of the heavy gun fire of the second parallel.

Captain W. Pratt, Fifty-fifth Massachusetts Volunteers, having been detailed by Brigadier-General Vogdes, at my request, for engineer duty, reported to-day.

The following instructions are approved by the general commanding, and take effect immediately:

HEADQUARTERS DEPARTMENT OF THE SOUTH, Engineer's Office, Morris Island, S. C., August 22, 1863.

Instructions for superintending engineer officers employed on the right and in advance of the first parallel, under direction of Captain Brooks, aide-de-camp and assistant engineer.

I. The sap+ which is in progress toward Fort Wagner is in charge of Captain Walker, assisted by Lieutenant Parsons, and Captain Suess, assisted by Lieutenant Wilcken, New York Volunteer Engineers.

Twenty-five men from Company I, under Sergeant [Cyrenius R.] Stickle and Corporals [John G.] Brooks and [Joseph] Longton as chiefs of sap; 12 men from Company B, under Sergeants [Henry] Fiene and [William] Huebbers as chiefs of sap; and 12 men from Company D, under Sergeants [Frederick] Buerkle and [Charles] Spilker as chiefs of sap, New York Volunteer Engineers, will be formed into four sapping brigades. The above-named officers will arrange their brigades, times of relief, &c., as they see fit. One-third the length of the sap must be fitted for infantry defense. The advanced guard of the trenches will furnish a constant detail of 20 infantry for duty in the sap, in accordance with written instructions given them.

Captains Walker and Suess will each report progress of themselves and assistants daily, according to inclosed form.++

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*See Note 16, p. 324.

+See Note 13, p. 323.

++Omitted.

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