produce only a certain amount of work--that is, the weight of a clock in descending or a spring in uncoiling returns theoretically the amount of work expended in raising or coiling it, and in no possible way can it do more. In practice, on account of friction, etc., we know it does less. This law, being invariable, of course limits us, as it did Archimedes and Pythagoras; we have simply utilized sources of power that their clumsy workmen allowed to escape. Of the four principal sources--food, fuel, wind, and tide--including harnessed waterfalls, the last two do by far the most work. Much of the electrical energy in every thunderstorm is also captured and condensed in our capacious storage batteries, as natural hygeia in the form of rain was and is still caught in our country cisterns. Every exposed place is crowned by a cluster of huge windmills that lift water to some pond or reservoir placed as high as possible. Every stiff breeze, therefore, raises millions of tons of water which operate hydraulic turbines as required. Incidentally these storage reservoirs, by increasing the surface exposed to evaporation and the consequent rainfall, have a very beneficial effect on the dry regions in the interior of the continent, and in some cases have almost superseded irrigation. The windmill and dynamo thus utilize bleak mountain-tops that, till their discovery, seemed to be but indifferent successes in Dame Nature's domain. The electricity generated by these, in connection with that obtained by waterfalls, tidal dynamos, thunderstorms, chemical action, and slow-moving quadruple-expansion steam engines, provides the power required to run our electric ships and water-spiders, railways, and stationary and portable motors, for heating the cables laid along the bottom of our canals to prevent their freezing in winter, and for almost every conceivable purpose. Sometimes a man has a windmill on his roof for light and heat; then, the harder the wintry blasts may blow the brighter and warmer becomes the house, the current passing through a storage battery to make it more steady. The operation of our ordinary electric railways is very simple: the current is taken from an overhead, side, or underneath wire, directly through the air, without the intervention of a trolley, and the fast cars, for they are no longer run in trains, make five miles a minute. The entire weight of each car being used for its own traction, it can ascend very steep grades, and can attain high speed or stop very quickly.
"Another form is the magnetic railway, on which the cars are wedge-shaped at both ends, and moved by huge magnets weighing four thousand tons each, placed fifty miles apart. On passing a magnet, the nature of the electricity charging a car is automatically changed from positive to negative, or vice versa, to that of the magnet just passed, so that it repels while the next attracts. The successive magnets are charged oppositely, the sections being divided halfway between by insulators, the nature of the electricity in each section being governed by the charge in the magnet. To prevent one kind of electricity from uniting with and neutralizing that in the next section by passing through the car at the moment of transit, there is a "dead stretch" of fifty yards with rails not charged at all between the sections. This change in the nature of the electricity is repeated automatically every fifty miles, and obviates the necessity of revolving machinery, the rails aiding communication. "Magnetism being practically as instantaneous as gravitation, the only limitations to speed are the electrical pressure at the magnets, the resistance of the air, and the danger of the wheels bursting from centrifugal force. The first can seemingly be increased without limit; the atmospheric resistance is about to be reduced by running the cars hermetically sealed through a partial vacuum in a steel and toughened glass tube; while the third has been removed indefinitely by the use of galvanized aluminum, which bears about the same relation to ordinary aluminum that steel does to iron, and which has twice the tensile strength and but one third the weight of steel. In some cases the rails are made turned in, so that it would be impossible for a car to leave the track without the road-bed's being totally demolished; but in most cases this is found to be unnecessary, for no through line has a curve on its vast stretches with a radius of less than half a mile. Rails, one hundred and sixty pounds to the yard, are set in grooved steel ties, which in turn are held by a concrete road-bed consisting of broken stone and cement, making spreading rails and loose ballast impossible. A large increase in capital was necessary for these improvements, the elimination of curves being the most laborious part, requiring bridges, cuttings, and embankments that dwarf the Pyramids and would have made the ancient Pharaohs open their eyes; but with the low rate of interest on bonds, the slight cost of power, and great increase in business, the venture was a success, and we are now in sight of further advances that will enable a traveller in a high latitude moving west to keep pace with the sun, and, should he wish it, to have unending day."
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
