The following letter was forwarded to Colonel Piatt, chief of staff:

Headquarters, Maryland Heights, June 26, 1863.

Lieutenant-Colonel Donn Piatt. Chief of Staff:

SIR: With all our telegraphing you cannot be fully posted up as to our doings here, and as the mails I think are safe, I shall write you fully up to this time . I will not attempt a description of the state in which I found matters here on assuming command . I am thankful I was not attacked then, and am fully indifferent as to whether I am attacked now. Colonel Raynols has been very busily engaged, and has, by various constructions, added very considerably to the defenses of the place. He is still at work, and in a few days the outline and essential parts of the fortifications will be so far finished as to be defensible, and they will be improved and completed by constant application of all the labor than can be employed on then. Since Colonel Raynolds arrived, the position of many of the guns has been shifted, and at this moment I believe all the artillery is posted in the best possible manner. As to the condition of the troops, it has considerably improved during the week and is fast improving. The men enter with spirit into the labor of throwing up the fortifications, and I see a growing confidence among officers and men that the works can be held against any force that will be probably brought against us. The men from Milroy's command are brigades with Smith 's men from Martinsburg, and are under the command of Brigadier-General Elliott, a complete officer, who is getting the brigade into the good fighting trim. In quartermaster's supplies we are short, the quartermaster having sent everything to Baltimore. We wants tents, camp equipage, clothing, &c., which are furnished by that department, and must have them. AS to commissary stores, we are, as I think, well enough off, having fifteen days ratios, and I deem this amount enough to keep here, for the reason that we have no store -house to receive them, and suppose the road between here and Baltimore can be so held that we cannot use it if absolutely necessary. I note what you as to the want of troops in Pe nnsylavnia ; still my impression is that the best place to reorganize Milroy's command here, even if you transfer to Pennsylvania a certain part of our garrison to replace them, I would willingly give one for two as fast as they came here. I do not think at this moment I would be gainer by the exchange, but I think the service would be greatly benefitted by the more speedy reorganization of Milroy's men, bringing the men of the different regiments of that command at once together. My telegrams have kept you posted as to the movements in my front. I am satisfied by this time that the Government is convinced that this is a movements of the bulk of Lee's army with Lee in command into Maryland and Pennsylvania. I am satisfied Ewell, Longstreet, and A. P. Hill, all Lee's corps commanders, are mow between Charlestown, Va., and Harrisburg, PA., and I think all those on this side of the Potomac. Colonel Jewett; s brigade, 1, 7000 strong, reported this morning. He belongs to Heintzelman; s corps, and is ordered here by Hooker. With it, I have force enough, and will hold myself responsible for this position. Colonel Jewett had orders to report me . I do not understand General Hooker's object, but probably shall through Major-General French.

With great respect, your obedient servant,

Dan. Tyler,

Brigadier-General.

Major-General French arrived, and issued the following orders:

General Orders, No. 14

Headquarters, Troops, Harper's Ferry, W. Va., June 26, 1863.

By virtue of Special Orders, No. 171, headquarters Army of Potomac, June 24, 1863 the undersigned assumes command of the troops at Harper's Ferry.

WM. H. French.

Major-General, U. S. Volunteers.

Special Orders, No. 12

Headquarters Troops, Harper's Ferry, W. Va., June 26, 1863.

Brigadier -General Tyler is relieved from duty with this command, and will report to Major- General French:

H. Y. Russell.

Lieutenant, and Aide-de-Camp.