It was a light structure, on wheels, carrying reels, from which there could be spun out insulated wire. It was fitted with telegraphic instruments of a kind before unused. it had been intended that the reels of this train should carry 10 miles of wire, so prepared that it might be laid on the ground and used anywhere without the escape of the electric current.
Different hindrances had made it impossible to furnish more than 4 miles of a copper were, coated with gutta-percha, and of a rather inferior quality. The magnetic electric instruments, devised for the train by a mechanic of New York,were of new invention. The working current for these instruments when placed on telegraphic line is generated by a pile of magnets-a part of the instrument itself. The letters of the alphabet are plainly on the dial. To cause the letters of the alphabet are plainly marked on the dial. To cause the letters to be indicated at either end of the line, or to read them are operations so simple as to be within the power, with little practice, of almost any soldier who can easily read and write. The instrument is used without fluids, without galvanic batteries of any kind, and is compact, strong, and portable. For use with flying telegraph trains on the field of battle, and for military telegraphing in general, I have regarded such instruments as necessary. I am of the opinion that it will be recalled at some time hereafter, with no little pride, that field telegraphic trains of this character and thus equipped were first brought into use by the Signal Corps of the Army, and were first used with the Army of the Potomac. The remains of this train, to which some historic interest already attaches, are now preserved at signal camp of instruction, Georgetown, D. C.
In the first attempts to experiment with and use this train an unexpected difficulty was encountered. The soldiers, unused to the coated wire, and seeing it stretched for miles along fences or lying on the ground near the road, would cut it and break it to examine its character. Some of them thought it an invention of the enemy.
On the 13th of May general headquarters were established at Cumberland. When, soon after our arrival here, the alarm was given that the headquarters train was endangered and that the enemy's forces were advancing, the general commanding, with his staff, started for the field in person. A detachment of five signal officers, equipped, accompanied him. The alarm was groundless.
There was some communication here by signals with the vessels in the river. A line of five signal stations was also established from this place to the advance guard under General Stoneman, the occupying White House. A few messages were sent to and from over this line, but its principal use was for practice.
On the 16th of may headquarters camp moved to White House, on the Pamunkey River. Among the reconnaissances made by signal officers from this place was one to the Chickahominy, near Bottom's Bridge, at, perhaps, the first time the waters of that stream were seen by any of our army.
On the ensuing day the corps commanded by General Keyes moving up to occupy a position near Bottom's Bridge, Lieutenant H. L. Johnson, acting signal officer, with a detachment of signal officers and their men, was ordered to report to and remain with him for duty. From that time until after the passage of the Chickahominy this detachment served under General Keyes, and always with the advance of the corps.
A station of observation was at once established near Bottom's Bridge whence the movements of the enemy whose pickets were now in sight