Captain SIMPSON, Topographical Engineers: The difficulty of our present position arises from the great facility the enemy has to concentrate troops at Winchester from Manassas Junction. By the railroad 12,000 men could be sent there in a day, and again sent back to Manassas. Our forces should combine with the forces at Washington.

Captain NEWTON, Engineers: Our present position is a very exposed one. General Johnston can keep us where we are as long as he pleases, and at any time make a demonstration on our rear. Our whole line is a false one. We have no business here except for the purpose of making a demonstration. He threatens us now. We should be in a position to threaten him. We should to to Charlestown, Harper's Ferry, Shepherdstown, and flank him.

Colonel STONE: It is mainly a question for the staff. Our enemy has great facility of movement, and to extend our line would be accompanied with great danger. Johnston should be threatened from some other point. We might leave two regiments here, two guns at Shepherdstown, and proceed to Charlestown, and threaten from that point.

General NEGLEY: Ditto to Captain Newton.

Colonel THOMAS: Approves of a flank movement to Charlestown.

Colonel ABERCROMBIE: The same.

General KEIM: The same.

General CADWALADER: Opposed to a forward movement.

WASHINGTON, July 11, 1861.

Major General PATTERSON, Martinsburg, Va.:

The author of the following is known, and he believes it authentic:

WASHINGTON, July 9, 1861.

The plan of operations of the secession army in Virginia contemplates the reverse of the proceedings and movements announced in the Express of yesterday and Saturday. A schedule that has come to light meditates a stand and an engagement by Johnston when he shall have drawn Patterson sufficiently far back from the river to render impossible his retreat across it on being vanquished, and an advance then by Johnston and Wise conjointly upon McClellan, and after the conquest of him, a march in this direction, to unite in one attack upon the Federal forces across the Potomac with the army under Beauregard at Manassas Junction and the wing of that army, the South Carolina regiments chiefly, now nine miles from Alexandria. Success in each of these three several movements is anticipated, and thereby not only the possession of the capital is thought to be assured, but an advance of the Federal troops upon Richmond prevented.

The plan supposes that this success will give the Confederate cause such prestige and inspire in it such faith as will insure the recognition of its Government abroad, and at the same time so impair confidence in the Federal Government as to render it impossible for it to procure loans abroad, and very difficult for it to raise means at home.

Real retreats, which have been anticipated, it will be seen, are by this plan altogether ignored. According to it, fighting and conquest are the orders.

W. SCOTT.

MARTINSBURG, VA., July 12, 1861.

Colonel E. D. TOWNSEND, Assistant Adjutant-General:

Dispatch of 11th received and confirms my impression expressed on 9th instant. To properly strengthen my position and secure line of communication, now insecure, and more so as wee advance; to insure expedition and continued success, I ask permission and a little time to transfer my depot to Harper's Ferry, and my forces on line of operations