It is a curious fact that the two factors most important in warfare were found to be two inventions designed primarily for the interests of peace, namely, the railroad and the electric telegraph. Steam and electricity had both been used in the Crimean and Italian wars; but it was in the War of Secession that they received their first great and systematic application. The effect of the use of railroads in war not only enables armies to be more rapidly concentrated than was formerly the case, but renders it possible to supply them to an extent and with a certainty that would otherwise be out of the question. The difference between the supply of an army by wagon and by rail was clearly shown in the siege of Paris, in 1870–71, where six trains a day fed the whole besieging army, while it is estimated that nearly ten thousand wagons would have been required for the same purpose. Moreover, the force of troops necessarily detached to protect a line of railroad communications is not nearly so great as the force that would be necessary to guard the innumerable wagon or pack trains that would otherwise be required. In the opinion of the best military authorities, railroads, had they been in existence, would have enabled Napoleon to conquer Russia, and with it the world; while, without the aid of railroads, the successful invasion of the South by the armies of the Union would have been an impossibility. It is only while it keeps moving that an army can “live on the country.” It is like a swarm of locusts, consuming everything within reach; and if it be compelled to halt, whether for battle or from other cause, it must be supplied from bases in the rear, or it will speedily disintegrate from hunger alone. This fact was fully appreciated by General Sherman, when he left Atlanta in his famous “march to the sea;” for though he expected to, and did, live upon the country, he nevertheless took the precaution to carry with him a wagon train containing twenty days’ rations for his entire army. In the War of Secession the electric telegraph first appeared on the field of battle. The telegraph train became a prominent feature of all our armies; and the day’s march was hardly ended before the electric wire, rapidly established by an expert corps, connected the headquarters of the army with those of each army corps, division, and brigade. But it was not in its employment on the actual field of battle that the telegraph found its most valuable military use. It enabled generals, separated by hundreds of miles, to be in constant communication with each other, and rendered it possible for Grant to control from his headquarters hut at City Point the movements of the armies of Sherman, Thomas, and Sheridan in combined operations, which enabled each to perform, in harmony with the others, its part in the mighty plan. [Illustration: SPENCER CARBINE.]