These air-lines are of two kinds: the anchored and the independent. The former are hung, by revolving wheels, upon great wires suspended in the air; the wires held in place by metallic balloons, fish-shaped, made of aluminium, and constructed to turn with the wind so as to present always the least surface to the air-currents. These balloons, where the lines cross the oceans, are secured to huge floating islands of timber, which are in turn anchored to the bottom of the sea by four immense metallic cables, extending north, south, east and west, and powerful enough to resist any storms. These artificial islands contain dwellings, in which men reside, who keep up the supply of gas necessary for the balloons. The independent air-lines are huge cigar-shaped balloons, unattached to the earth, moving by electric power, with such tremendous speed and force as to be as little affected by the winds as a cannon ball. In fact, unless the wind is directly ahead the sails of the craft are so set as to take advantage of it like the sails of a ship; and the balloon rises or falls, as the birds do, by the angle at which it is placed to the wind, the stream of air forcing it up, or pressing it down, as the case may be. And just as the old-fashioned steam-ships were provided with boats, in which the passengers were expected to take refuge, if the ship was about to sink, so the upper decks of these air-vessels are supplied with parachutes, from which are suspended boats; and in case of accident two sailors and ten passengers are assigned to each parachute; and long practice has taught the bold craftsmen to descend gently and alight in the sea, even in stormy weather, with as much adroitness as a sea-gull. In fact, a whole population of air-sailors has grown up to manage these ships, never dreamed of by our ancestors. The speed of these aerial vessels is, as you know, very great--thirty-six hours suffices to pass from New York to London, in ordinary weather. The loss of life has been less than on the old-fashioned steamships; for, as those which go east move at a greater elevation than those going west, there is no danger of collisions; and they usually fly above the fogs which add so much to the dangers of sea-travel. In case of hurricanes they rise at once to the higher levels, above the storm; and, with our increased scientific knowledge, the coming of a cyclone is known for many days in advance; and even the stratum of air in which it will move can be foretold.