1. It is so situated as to give you the best possible position to observe the enemy and to obtain the very earliest possible information as to any movement he can make towards Washington.

2. It is the strongest and most defensible military position, except that about Shooter's Hill, that I have seen between Washington and four miles of Fairfax Court-House, and is so situated that it must be attacked and carried before it would be safe for any enemy to make and forward movement on Ball's Cross-Roads or Bailey's Cross-Roads, as a movement on Baily's Cross-roads would expose the enemy to a flank attack from the troops situated at Falls Church and a movement on Ball's Cross-Roads to a rear attack, and neither of these crossings is more than two and a half miles from Falls Chruch.

3. As the enemy's pickets before our arrival here were in possession of the ground in our front, I am satisfied the moment we leave the position it will be occupied, and, in connection with the possession of Vienna, will give him the possession of a line that it will cost us thousands of men to drive him from it, and we shall have to do it if is strong enough to sustain an advance.

4. A retrograde, if followed by the occupation of the Falls Church position, as it will be, will enable the enemy to control the entire valley of the Four Mile Run, from Vienna to within two miles of roach's Mills, and if they have twenty thousand men, everything else being equal fifty thousand men cannot drive them out.

5. A retrograde movement (I will no consider its effects on the country) will have a most injurious effect on the Union men in this vicinity (and they are in considerable number), and thus must necessarily leave with us or be killed.

The above, general, are only some of the reasons that present themselves to my mind in opposition to a retrograde movement, which I think can be prevented and our position here perfectly secured by posting three regiments at Ball's Cross-Roads and as many at Bailey' Cross-Road,which will bring the whole front from Georgetown, Falls Church, and Alexandria within short supporting positions. With a single battery of light artillery and a couple of hundred of cavalry, with two Connecticut and the two Ohio regiments, I can hold our position at Falls Church for two hours against ten thousand men, counting time from the moment our pickets will notify us of the approach of the enemy, and that will give us time to be supported from Ball's and Bailey's Cross-Roads and the New Jersey regiments at Roach's Mills, leaving the troops at Alexandria and those in the vicinity of Arlington, Georgetown, and Washington near enough to sustain us in case we should be overmatched,which I do not think we should be. At all events, we would give time enough for these troops to come to our relief.

Before a retrograde movement is made I would like to canvass this matter with yourself and General Scott. Since I came here any mind has been constantly occupied with the subject of my position here, and I think I understand as well as any engineer officer or officers who may come out here and pass half and hour examining it and then return to Washington with a report. I know that these things must be, but I must confess that I felt mortified that two gentleman of the Engineers should come into my camp under instructions, as I now find, to examine and pass upon the most important military positions in our whole line, which had been selected by me, and not have the courtesy to invite my attendance or call my attention to the fact that they were on any official duty.

When I had the honor to have a commission in the line of the United