Doc. 129.-the Morse magnetic telegraph. Its Utility to General McClellan.The following letter from Parker Spring, Superintendent Construction of United States Military Telegraph Lines, gives an interesting account of the services of the Morse telegraph to the army, and of Gen. McClellan's use of it:
United States military telegraph, headquarters Department Potomac, Gaines's Hill, seven miles from Richmond, June 2.From the time the army of the Potomac first left Washington the United States Military Telegraph has never for an hour been allowed to remain in the rear. Before reaching his new headquarters Gen. McClellan almost invariably learns that the wire is on the advance; that an office has already been opened at the point designated before he left his old camp, and that communication to the War Department at Washington is open for him. In several instances when the army had marched fifteen miles in one day, the telegraph had reached the new quarters two hours in advance. When our troops are obliged to remain a few days in one position, wires are immediately run from Gen. McClellan's quarters to the headquarters of all commanders of divisions, thereby placing the entire section of country occupied by our troops under his instant control Assistance like this is surely valuable to our glorious cause, and, I am happy to say, it is fully appreciated by the General. Saturday previous to the evacuation of Yorktown, Gen. McClellan ordered me to run a wire into our Battery No. 6, in order to give him telegraphic communication from his headquarters, which were distant about one and a half miles. This battery laid half a mile in front of General Heintzelman, and within half a mile of a long chain of rebel batteries. The office at Battery No. 6 was to be located under ground, in a bombproof arrangement, in order to save the precious life of the manipulator, who would be in his hole before day break the next morning. I was informed by Gen. Heintzelman's aids that it was a very hazardous experiment; that from the point where the line must cross the fields the rebel officers could be heard distinctly giving command; that the rebel pickets were within two hundred and fifty yards of us, and if we attempted to distribute poles with our wagon we would be fired upon. Of these facts I informed all our men. Regardless of danger, they unanimously voted for the extension. Fortunately that night was dark, and promptly at nine P. M. we were in readiness to commence operations. After cautioning all hands to work quietly, I detailed the men as follows: Cosgrove, Hoover, Greiner and McGuire to dig holes; Rote, Keiler, Benedict and Jones to distribute poles on their shoulders, who had to carry them a full mile. John Tryer I posted as guard. His duty was to watch the flash of the rebel guns, and notify the men, who were working and could not see, when to fall on the sod, should the rebels hear us and open. Thus far all was quiet in the secesh quarters. Scarcely had our operations commenced when a compliment from Gen. Magruder in the shape of a shell was sent us. Through the timely notice received from our guard, Mr. Tryer, that “he saw a flash, and that something with a flery tail was coming toward us,” we were enabled to drop. It came within fifty yards of us, bursted, but did no damage. After that shot and shell followed in rapid succession, until we completed our task, which, owing to loss of time in dodging, occupied fully five hours. A number of these missiles fell within thirty feet of us, showing conclusively that the rebel pickets had discovered our operations, and were directing the fire of their artillery. We have preserved pieces of a shell that knocked down a pole behind us, which had been erected not five minutes before the shot was fired. The line was run through a soft corn-field, and it was amusing next day, after the evacuation, when we returned to this field, to see the life-like pictures of Tryer, Cosgrove, and several others, nicely portrayed in the mud, and which no artist in the world could excel. They were at once recognized by all hands, and I promised to give you the particulars. The telegraph has been called upon to perform a still more mysterious wonder. For some time past I have been ordered by Col. Eckert (our superintendent of military telegraphs) to try a telegraphic experiment from a balloon. Saturday  morning, when we heard that a great battle must be fought, Professor Lowe notified me that I should extend the wire to his balloon, and we would try it. In one hour we had brought the wire a mile and a half, and I was ready to ascend with the Professor. The battle had commenced. When it had reached its zenith, Professor Lowe and myself, with the telegraph, had reached an altitude of two thousand feet. With the aid of good glasses we were enabled to view the whole affair between these powerful contending armies. As the fight progressed, hasty observations were made by the Professor and given to me verbally, all of which I instantly forwarded to General McClellan and division commanders through the agency of the obedient field instrument which stood by our side in the bottom of the car. Occasionally a masked rebel battery would open upon our brave fellows. In such cases the occupants of the balloon would inform our artillerists of its position, and the next shot or two would, in every case, silence the masked and annoying customers. For hours, and until quite dark, we remained in the air, the telegraph keeping up constant communication with some point. From the balloon to Fortress Monroe, a distance of over a hundred miles, this wire worked beautifully. A number of messages were sent and received between these two points, and had it not been for the tremendous rush of business on the wire, I should have telegraphed you directly from the balloon, while the battle was raging. Sunday morning, at daybreak, we again ascended. Early in the morning the battle was renewed, and with more fierceness than the day before. Incessant firing of musketry and artillery was kept up until noon, when I had the extreme pleasure to announce by telegraph from the balloon, that we could see the enemy retreating rapidly toward Richmond. At this time we could see firing on James River, to the left of Richmond, distance from the balloon, some said, fifteen miles. This fire was of short duration. The streets of Richmond in the morning presented a deserted appearance, but very few people to be seen in the streets. During the afternoon and evening of Sunday nothing of interest transpired beyond the removal of the rebel dead and wounded, all of which we could distinctly see from the balloon. Every available machine that had wheels was brought into requisition for this purpose. From the scene of battle into the city of Richmond, the road was literally lined with ambulances, wagons and carts, conveying dead and wounded. About twilight we saw eamp-fires innumerable around the city; smoke issued from all their hospitals and barracks, which showed us to a certainty that the main body of their army had fallen back to Richmond. Monday morning we made several ascensions, and found a small force near the last scene of action, and thousands of troops marching out from the city, so you may look momentarily for a report of another severe battle. I am going to continue my ascensions with Professor Lowe, and should I have an opportunity to give you a telegraphic report from the balloon without a violation of the General's Order to correspondents, you shall have it. Our experiments have met the approbation of all officers. Balloon telegraphing is fully established, and I am very happy to inform you that we are the first who have established it successfully. A feeble attempt to telegraph from a balloon was made in Washington last summer, of which I will give you a correct description, and bring good testimony to show it was a complete fizzle. Newspapers were filled with accounts of this wonderful experiment. Messages appeared as having been sent to the President and other distinguished individuals. The balloon ascended — so did the telegraph. Not until they had descended as low as the house-tops was the message started. Two thirds of it was sent after the balloon had delivered its passengers safely on terra firma. It was such a complete failure that the operator, W. B. Wilson, then at the War Department, who was to receive the despatch, refused to copy it, he having himself seen the balloon landed on the ground, after receiving the first few words. To this Professor Lowe himself will certify.--Lancaster, Pa., Express.