Chapter V.Contents
DR. CORTLANDT'S HISTORY CONTINUED.
"In marine transportation we have two methods, one for freight and another for passengers. The old-fashioned deeply immersed ship has not changed radically from the steam and sailing vessels of the last century, except that electricity has superseded all other motive powers. Steamers gradually passed through the five hundred-, six hundred-, and seven hundred-foot-long class, with other dimensions in proportion, till their length exceeded one thousand feet. These were very fast ships, crossing the Atlantic in four and a half days, and were almost as steady as houses, in even the roughest weather.
"Ships at this period of their development had also passed through the twin and triple screw stage to the quadruple, all four together developing one hundred and forty thousand indicated horse-power, and being driven by steam. This, of course, involved sacrificing the best part of the ship to her engines, and a very heavy idle investment while in port. Storage batteries, with plates composed of lead or iron, constantly increasing in size, had reached a fair state of development by the close of the nineteenth century.
"During the second decade of the twentieth century the engineers decided to try the plan of running half of a transatlantic liner's screws by electricity generated by the engines for driving the others while the ship was in port, this having been a success already on a smaller scale. For a time this plan gave great satisfaction, since it diminished the amount of coal to be carried and the consequent change of displacement at sea, and enabled the ship to be worked with a smaller number of men. The batteries could also, of course, be distributed along the entire length, and placed where space was least valuable.
"The construction of such huge vessels called for much governmental river and harbour dredging, and a ship drawing thirty-five feet can now enter New York at any state of the tide. For ocean bars, the old system of taking the material out to sea and discharging it still survives, though a jet of water from force-pumps directed against the obstruction is also often employed with quick results. For river work we have discovered a better method. All the mud is run back, sometimes over a mile from the river bank, where it is used as a fertilizer, by means of wire railways strung from poles. These wire cables combine in themselves the functions of trolley wire and steel rail, and carry the suspended cars, which empty themselves and return around the loop for another load. Often the removed material entirely fills small, saucer-shaped valleys or low places, in which case it cannot wash back. This improvement has ended the necessity of building jetties.
"The next improvement in sea travelling was the 'marine spider.' As the name shows, this is built on the principle of an insect. It is well known that a body can be carried over the water much faster than through it. With this in mind, builders at first constructed light framework decks on large water-tight wheels or drums, having paddles on their circumferences to provide a hold on the water. These they caused to revolve by means of machinery on the deck, but soon found that the resistance offered to the barrel wheels themselves was too great. They therefore made them more like centipeds with large, bell-shaped feet, connected with a superstructural deck by ankle-jointed pipes, through which, when necessary, a pressure of air can be forced down upon the enclosed surface of water. Ordinarily, however, they go at great speed without this, the weight of the water displaced by the bell feet being as great as that resting upon them. Thus they swing along like a pacing horse, except that there are four rows of feet instead of two, each foot being taken out of the water as it is swung forward, the first and fourth and second and third rows being worked together. Although, on account of their size, which covers several acres, they can go in any water, they give the best results on Mediterraneans and lakes that are free from ocean rollers, and, under favourable conditions, make better speed than the nineteenth-century express trains, and, of course, going straight as the crow flies, and without stopping, they reach a destination in considerably shorter time.
"Some passengers and express packages still cross the Atlantic on 'spiders,' but most of these light cargoes go in a far pleasanter and more rapid way. The deep-displacement vessels, for heavy freight, make little better speed than was made by the same class a hundred years ago. But they are also run entirely by electricity, largely supplied by wind, and by the tide turning their motors, which become dynamos while at anchor in any stream. They therefore need no bulky boilers, engines, sails, or coal-bunkers, and consequently can carry unprecedentedly large cargoes with comparatively small crews. The officers on the bridge and the men in the crow's nest--the way to which is by a ladder INSIDE the mast, to protect the climber from the weather--are about all that is needed; while disablement is made practically impossible, by having four screws, each with its own set of automatically lubricating motors.
"This change, like other labour-saving appliances, at first resulted in laying off a good many men, the least satisfactory being the first to go; but the increase in business was so great that the intelligent men were soon reemployed as officers at higher rates of pay and more interesting work than before, while they as consumers were benefited as much as any one else by the decreased cost of production and transportation.
"With a view to facilitating interchange still further, our Government has gradually completed the double coast-line that Nature gave us in part. This was done by connecting islands separated from shore by navigable water, and leaving openings for ingress and exit but a few hundred yards wide. The breakwaters required to do this were built with cribbing of incorrodible metal, affixed to deeply driven metallic piles, and filled with stones along coasts where they were found in abundance or excess. This, while clearing many fields and improving them for cultivation, provided just the needed material; since irregular stones bind together firmly, and, while also insoluble, combine considerable bulk with weight. South of Hatteras, where stones are scarce, the sand dredged from parts of the channel was filled into the crib, the surface of which has a concave metallic cover, a trough of still water being often the best barrier against the passage of waves. This double coast-line has been a great benefit, and propelled vessels of moderate draught can range in smooth water, carrying very full loads, from Labrador to the Orinoco. The exits are, of course, protected by a line of cribbing a few hundred feet to seaward.
"The rocks have been removed from all channels about New York and other commercial centres, while the shallow places have been dredged to a uniform depth. This diminishes the dangers of navigation and considerably decreases the speed with which the tides rush through. Where the obstructions consisted of reefs surrounded by deep water, their removal with explosives was easy, the shattered fragments being allowed to sink to the bottom and remain there beneath the danger line.
"Many other great works have also been completed. The canals at Nicaragua have been in operation many years, it having been found best to have several sizes of locks, and to use the large ones only for the passage of large vessels. The improved Erie and Champlain Canals also enable ships four hundred feet long to reach New York from the Great Lakes via the Hudson River.
"For flying, we have an aeroplane that came in when we devised a suitable motor power. This is obtained from very light paper-cell batteries that combine some qualities of the primary and secondary type, since they must first be charged from a dynamo, after which they can supply full currents for one hundred hours--enough to take them around the globe--while partly consuming the elements in the cells. The power