The mortar schooners have been firing on Wagner yesterday and to-day. One of their shells dropped in our advanced trenches and killed 1 man.

It is anticipated that the sap will have to advance from the third parallel against an artillery fire from Wagner, more or less severe, and as it is believed that the fort has at least one rifled gun bearing this way, serious annoyance is feared. To advance under this fire, a system of blinded direct sap, or surface mining, has been considered and experimented upon. It is intended to protect the approaches from all horizontal, and from the splinters of a vertical, fire. This method could not be employed, as was afterward ascertained, because it required a depth of 4 feet of earth, which could only be found for a very small portion of the distance.

Capts. Joseph Walker and John L. Suess have been detailed on sapping duty, and are now engaged in drilling four brigades of sappers from Companies I, B, and D, New York Volunteer Engineers. The full sap, rivetted with gabions and without any rivetting material whatever, has been executed for practice.* In the latter method, the parapet is kept closed upon the sap-roller, which is moved forward but a few inches at a time. Captain Walker is the special advocate of the last plan, which was afterward chiefly used, and found to work well. It is slow, but has the advantage of not requiring instructed sappers or rivetting material.

Sunday, August 16.-To-day Lieutenant-Colonel Sleeper, Fourth New Hampshire Volunteers, with a detail of 30 men from his own regiment, is making gabions+ on Black Island. The same work is in progress on Folly Island, under Lieutenant J. H. Harrold, New York Volunteer Engineers.

Built splinter-proof shelter in rear of Battery Kearny, for use of artillerists serving its guns. Continued repairs on rivetting of second parallel. Three hundred and sixty linear yards of wide and narrow splinter-proof shelter,++ capable of accommodating over 1,000 men, are finished, and the work of its construction is suspended for the present. Corporal [Jacob] Steinhilber, Company D, New York Volunteer Engineers, assisted in its erection.

Brigadier General A. H. Terry, commanding forces on Morris Island, requested to-day that a parapet be built sufficiently strong to shelter the brigade which will be stationed near the Beacon House, as a reserve during the bombardment, which will begin to-morrow morning. The general commanding approved the plan. Accordingly, this night, Captain S. C. Eaton, New York Volunteer Engineers, with an infantry detail of 300 men, built 750 yards of splinter-proof parapet, 6 1/2 feet high, extending from the Beacon House southerly along extreme high-water line. At the same time, Captain Graef built the approach from the Beacon House to the first parallel, thus supplying a link, the want of which, for its moral effect on the men entering the trenches, has frequently been felt.

Twenty-five sand-bags for each breaching gun were filled and piled up in rear of the batteries, to be used for repairs during the fight. A large quantity of engineering material,@ consisting of sand-bags, gabions, fascines, lumber, hides, ropes, spikes, abatis material, &c., is collected at the engineer service depot@ in the second parallel, for use in repairs during the bombardment.

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*See Note 13, p. 323.

+See Note 9, p. 317.

++See Note 21, p. 331.

@See Notes 6, 7, and 8, pp. 312-316.

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