HEADQUARTERS DEPARTMENT OF PENNSYLVANIA,
Chambersburg, Pa., June 15, 1861.

Captain JOHN NEWTON,

Engineer Corps, en route to Williamsport:

CAPTAIN: In reply to your note of this date, I have, by direction of the commanding general, hastily addressed a letter to General Cadwalader authorizing him to throw a force beyond Williamsport, and to send in advance towards Martinsburg parties to secure against surprise, provided the report you send that Harper's Ferry is vacated be true. He is advised to send you to reconnoiter carefully, and as you know the wishes of the commanding general and the momentous interests at stake, which would suffer even from a check, which would be constructed into a victory, to take your advice into consideration and act upon it, knowing, as does the commanding general, that he can rely upon your judgment and prudence not to compromise our present position. You understand the condition of the Army and the impossibility of advancing far with any large portion of our force, and the danger of having a portion cut off. If the enemy has abandoned Harper's Ferry, the commanding general wishes it occupied as soon as it can be done safely.

I am, captain, very respectfully, your obedient servant,

F. J. PORTER,

Assistant Adjutant-General.

P. S.-We will be at Hagerstown to-night. Keep the general well informed by expresses.

CHAMBERSBURG, PA., June 15, 1861.

Major General GEORGE CADWALADER,

Commanding First Division, en route to Williamsport:

GENERAL: The commanding general desires you to give Captain Newton the necessary aid to carefully reconnoiter the position of the enemy beyond Williamsport, to ascertain if he is really vacating the borders of the Potomac in your vicinity. If the has vacated, the commanding general wishes you to throw a portion, if not the whole, of your division over the river, and send parts well in advance to secure against surprise, and, if it can safely be done, to annoy their retreat. Captain Newton will advise you of the wishes of the commanding general, and his advice you are desired to take into careful consideration for the purpose of acting upon. If you find the enemy gone, the general wishes General Wynkoop placed as soon as possible near the river, on your line, and General Williams advanced towards Sheperdstown.

I am, general, very respectfully, your obedient servant,

F. J. PORTER,

Assistant Adjutant-General.

P. S.-If Harper's Ferry is abandoned, send a force there. Keep the general well advised by expresses. If it be possible, the general will be at Hagerstown to-night.

CHAMBERSBURG, PA, June 15, 1861.

Brevet Major General GEORGE CADWALADER,

Commanding First Division, Pennsylvania Volunteers:

GENERAL: Cumberland is threatened by a large force (three thousand men) and asks for aid. If you are certain that the enemy has