My own prepossessions had been in favor of the Birago system of sectional pontoons and Birago (so called) trestles. The experience we had proved the wisdom which adopted the system in question. Not to advance, by any means, that nothing better can be found (the substitution of iron for wood was one of the probable improvements well understood by the officers named, but not at that time adopted for substantial reasons), it is enough to say that the French pontoon was found to be most excellent, useful, and reliable for all military purposes. They were used by the quartermaster's department in discharging transports, were precisely what was needed for the disembarkation of General Franklin's division, constituted a portion of the numerous bridges built over Wormley's Creek during the siege of Yorktown, and were of the highest use on the Chickahominy, while over the Lower Chickahominy some 75,000 men, some 300 pieces of artillery, and the immense baggage trains of the army passed over a bridge of the extraordinary length of nearly 650 yards-a feat scarcely surpassed in military history.

The Birago trestle, of which I had formed so high an opinion, proved itself dangerous and unreliable-useful for an advance guard or detachment, unfit in general for a military bridge. Of the American Indiarubber and the Russian canvas pontoon we had no fair experiment. they may both be useful, but, again, I think not reliable for a military bridge, considered in all its aspects and uses.

The weight of the French pontoons is objected to, but a certain floatation power is required which it is not easy to get, nor are the ways unobjectionable which seek to get it which less weight, and the vehicle which carries it is not heavier loaded than other vehicles of an army train. Less length would certainly make it more manageable on our narrow roads, while for advance guards and dashing minor enterprises greater lightness is requisite. Perhaps an iron sectional pontoon may be contrived which will meet these requirements, but prudence demands that the safety of an army shall not be jeopardized by giving it a bridge which experiment has not fully tested.

American genius is fertile in this as in all other expedients, but no genius can provide for an object which is not understood. The numerous proposers of flying bridges forget that if a military bridge is intended to be carried with an army it is also intended to carry an army, its columns of men, its cavalry, its countless heavy wagons, and its ponderous artillery. It must carry all these, and it must do it with certainty and safety, even though a demoralized corps should rush upon it in throngs. No make-shift expedient, no ingenious inventions not tested by severe experiment, nor light affair, of which the chief merit alleged is that it is light, will be likely to do what is required, and what the French pontoon has so often done.

Here, perhaps, I might close, but it occurs to me that this paper, purporting to give a history of the operations of engineers from the organization of the Army of the Potomac to the close of its campaign on the Peninsula, can hardly be considered complete without a retrospect, pointing out the mistakes that were made, and thus tracing the causes of its failure to their true sources.

One of the prominent among the causes of the ultimate failure was the inaction of eight months, from August, 1861, to April, 1862. More than any other wars, rebellion demands rapid measures. In November, 1861, the Army of the Potomac, if not fully supplied with all the material, yet was about as complete in numbers, discipline, and organization as it ever became. For four months the great marine avenue to