drawing of which you have in your office. For deep and narrow streams, for torrents, or where ice may be encountered, I have not a doubt but that the suspension principle is the correct one. Three or four spans of this bridge might be ordered, and I should suppose could soon be made. It appears to me, however, that manila rope ought to replace the wire rope for all running rigging, and in all cases, except for the suspension cables. It is easier repaired, and our troops will more readily understand it. We can go to New York and get 10,000 men to splice or put a thimble in a manila rope. By going to Mr. Roebling's establishment in Trenton it is possible that we might find 20 men who could do the same thing with a wire rope.

These would give us half a dozen complete bridges, adapted to different circumstances. The experience acquired in their construction would lead to improvements and perhaps to the adoption of other bridges. It should not be forgotten that in any advance of our army we ought to avail ourselves of the mechanical skill of our soldiers and the timber of the country to replace all such bridges, where it is possible, by more permanent structures. In many cases ferry-boats may be made to take the place of bridges if we carry the necessary tools with which to construct them and the necessary rigging with which to maneuver them in the engineer trains.

After we shall have obtained the necessary engineer troops, and provided bridge equipages, entrenching and siege tools, we will be prepared to commence the instruction of our troops in the operations of a siege-in making fascines, gabions, and sap-rollers, and in the method of laying out and constructing approaches.

But as I did not propose to enter into any discussion of this subject at present, I will close with only this allusion to is, which will serve to remind us how much we have to do and how much we have to learn before can place ourselves in a condition to commence the siege of any fortified place.

Very respectfully, your obedient servant,

B. S. ALEXANDER,

Lieutenant-Colonel Engineers.

HEADQUARTERS ARMY OF THE POTOMAC,
Washington, October 14, 1861.

Honorable THOMAS A. SCOTT,

Assistant Secretary of War:

SIR: On Friday last [October 12] I had the honor to address to the War Department a communication, in which I requested authority to cause the construction of from ten to fifteen of the Birago bridge trains, referring also to other matters pertaining to the engineer service. A more full consideration of the subject has convinced me that we may not have time enough to construct the necessary numbers of bridge trains of that peculiar pattern, although it is the best now in use in Europe. As the exigency of the case admits of no delay, I would respectfully suggest to be immediately empowered to have bridge trains constructed in such numbers and of such kinds as may prove to be best adapted to our wants. It is necessary to avail ourselves at once of all the refurnish in this matter. As much time is necessary to prepare these trains, I would respectfully request an immediate answer to this communication, as well as to the other requests embodied in my letter of Friday.