ONE of the greatest secret forces in the Civil War was the electric telegraph. Wires were uncoiled as the army moved on its march toward the enemy and over them passed the hurried words that frequently saved hundreds and thousands of lives. While England was the first to experiment with the new science on the battlefield, the war in America demonstrated its permanent importance in the maneuvers of armies. Brady was much interested in the development of telegraphy as a factor in war and never missed any opportunity to take a photograph of the field telegraph corps as they passed him on marches. This picture shows one of the construction corps in operation. The wires were laid as each column advanced, keeping the General in command fully informed of every movement and enabling him to communicate from his headquarters in the rear of the army with his officers in charge of the wings. The military construction corps laid and took up these wires as fast as an infantry regiment marches. An instant's intelligence may cause a charge, a flank or a retreat. By connecting with the semi-permanent lines strung through woods and fields, into which the enemy would have little reason to venture unless aroused by suspicion, the commander on the field is kept informed of the transportation of troops and supplies and the approach of reinforcements. It was also the duty of the military construction corps to seize all wires discovered by them and to utilize them for their own army or tear them down. Constant watch is kept for these secret lines. Great care must also be taken that false messages do not pass over them. Their destruction is generally left to the cavalry. The heavy construction wagons, carrying many miles of telegraph wire in coils, were drawn by four horses. [Illustration: PHOTOGRAPH TAKEN AS MILITARY TELEGRAPH WAS BEING STRUNG] [Illustration: PHOTOGRAPH TAKEN AS FIELD TELEGRAPH WAGON WAS SENDING MESSAGE]