"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.
