1. Federal Hill, 83 feet 6 inches above mean high tide.-It is to be immediately entrenched by order of the General-in-Chief in accordance with the suggestions in my letter of the 12th instant. Next to Fort McHenry it is the most important position in the harbor of Baltimore. It command the railroad through Pratt street to the President-street depot, the entire basin, the whole lower part of the city, and in the hands of an enemy might be dangerous to Fort Henry, from which it is 2 miles distant. The distance to Pratt street at the head of the basin is about 800 yards.

2. Patterson's Park, 124 feet 9 inches above mean high tide.-A commanding position, 2 miles from Fort McHenry, and would b very important if Numbers 3 (Potter's Race Course) were not ot be fortified. It is surrounded by a loyal population, and its present occupation is not as necessary as that of Numbers 4 (the McKim mansion). A regiment has been encamped there until recently. It has been unoccupied since the 7th instant, when the Sixth Wisconsin Regiment was ordered to Washington.

3. Potter's Race Course, 180 feet above mean high tide.-A strong work on this height is indispensable to the safety of Fort McHenry, which it commands, and from which it is less than 2 miles distant. It also commands Patterson's Park, and is the only point, with the exception of the latter and Numbers 4, from which the eighth ward, one of the most disloyal in the city, and be assailed. it is to be immediately fortified by order of the General-in-Chief.

4. McKim's Mansion, 119 feet 9 inches above mean high tide.-It is in the eighth ward, and commands that portion of the city as effectually as Federal hill commands the lower portion and the basin. For controlling the population of the city and suppressing outbreaks this position is second only to the latter. It was occupied by the Fifth Wisconsin Regiment until the 7th instant, when that regiment was ordered to Washington. If I had a regiment to spare I should place it here in preference to Paterson's Park. It has excellent and ample ground for battalion drill.

5. Steuart's Mansion, Mount Clare, 184 feet 7 inches above mean high tide.-This position is important from its vicinity to the Baltimore and Ohio Railroad and the Mount Clare depot on that road, as well as from the relation it holds to the direction from which the city is most likely to be assailed from without. It is occupied by the Fourth Pennsylvania Volunteers, numbering 823 men, and Nims' Boston Light Artillery, numbering 156. The Second Maryland Regiment (six companies) is encamped on the line of the same railroad and in the same neighborhood with 579 men. I have therefore in this locality 1,558 men.

My force is disposed as follows:

Fort McHenry, inside: Regulars, 194; outside: Third New York Volunteers, 795; Twenty-first Indiana Volunteers, 845. Total, 1,843.

Federal Hill: Fifth New York Volunteers, Colonel Duryea, 1,028.

Mount Clare: Fourth Pennsylvania, 823; Second Maryland, 579; Nims' Light Artillery, 156. Total, 1,558.

Agricultural Ground, north of the city: Two companies of Pennsylvania Cavalry, unequipped, 213. Grand total, 4,633.

My effective force is under 4,000. I need three regiments more. The first I shall place at Numbers 3 (Potter's Race Course) to work on the proposed entrenchments; the second at Numbers 4 (McKim's mansion) to take care of the eighth ward, and the third at Numbers 2. (Patterson's Park) until Numbers 3 is fortified. The home guard is in course of organizing in the city, and I think can be armed next week. It will number 850 men.