Once upon a time a man hollowed a tree, and, launching it upon the water, found that it would bear him up.  After this a few little floats, creeping cautiously near the land, were all on which men were wont to venture. Now there are sails fluttering on every sea, prodigious steamers throbbing like leviathans against wind and wave; harbors are built, and rocks and shoals removed; lighthouses gleam nightly from ten thousand stations on the shore; the great deep itself is sounded by plummet and diving-bell; the submarine world is disclosed; and man is gathering into his hands the laws of the very winds that toss its surface.

Once the earth had a single rude, mud-built hamlet, in which human dwellings were first clustered together. Now it is studded with splendid cities, strewn thick with towns and villages, diversified by infinite varieties of architecture:  sumptuous buildings, unlike in every clime, each as if sprung from its own soil and made out of its air.

Once there were only the elementary discoveries of the lever, the wedge, the bended bow, the wheel; Tubal worked in iron and copper, and Naamah twisted threads.  Since then what a jump the mechanical arts have made!  These primitive elements are now so intricately combined that we can hardly recognize them; new forces have been added, new principles evolved; ponderous engines, like moving mountains of iron, shake the very earth; many-windowed factories, filled with complex machinery driven by water or its vapor, clatter night and day, weaving the plain garments of the poor man and the rich robes of the prince, the curtains of the cottage and the upholstery of the palace.

Once there were but the spear and bow and shield, and hand-to-hand conflicts of brute strength.  See now the whole enginery of war, the art of fortification, the terrific perfection of artillery, the mathematical transfer of all from the body to the mind, till the battlefield is but a chess-board, and the battle is really waged in the brains of the generals.  How astonishing was that last European field of Solferino, ten miles in sweep,—­with the balloon floating above it for its spy and scout,—­with the thread-like wire trailing in the grass, and the lightning coursing back and forth, Napoleon’s ubiquitous aide-de-camp,—­with railway-trains, bringing reinforcements into the midst of the melee, and their steam-whistle shrieking amid the thunders of battle!  And what a picture of even greater magnificence, in some respects, is before us to-day!  A field not of ten, but ten thousand miles in sweep!  McClellan, standing on the eminence of present scientific achievement, is able to overlook half the breadth of a continent, and the widely scattered detachments of a host of six hundred thousand men.  The rail connects city with city; the wire hangs between camp and camp, and reaches from army to army.  Steam is hurling his legions from one point to another; electricity brings him intelligence, and carries his