the history of the telephone-第15节
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emergencies； began in 1882 a series of actual experiments at Attleborough； Massachusetts； to find out exactly what could； and what could not； be done with wires that were buried in the earth。
A five…mile trench was dug beside a railway track。 The work was done handily and cheaply by the labor…saving plan of hitching a locomotive to a plough。 Five ploughs were jerked apart before the work was finished。 Then； into this trench were laid wires with every known sort of covering。 Most of them； naturally； were wrapped with rubber or gutta…percha； after the fashion of a submarine cable。 When all were in place； the willing locomotive was harnessed to a huge wooden drag； which threw the ploughed soil back into the trench and covered the wires a foot deep。 It was the most professional cable… laying that any one at that time could do； and it succeeded； not brilliantly； but well enough to encourage the telephone engineers to go ahead。
Several weeks later； the first two cables for actual use were laid in Boston and Brooklyn； and in 1883 Engineer J。 P。 Davis was set to grapple with the Herculean labor of putting a
complete underground system in the wire…bound city of New York。 This he did in spite of a bombardment of explosions from leaky gas… pipes； and with a woeful lack of experts and standard materials。 All manner of makeshifts had to be tried in place of tile ducts； which were not known in 1883。 Iron pipe was used at first； then asphalt； concrete； boxes of sand and creosoted wood。 As for the wires； they were first wrapped in cotton； and then twisted into cables； usually of a hundred wires each。 And to prevent the least taint of moisture； which means sudden death to a telephone current； these cables were invariably soaked in oil。
This oil…filled type of cable carried the telephone business safely through half a dozen years。 But it was not the final type。 It was preliminary only； the best that could be made at that time。 Not one is in use to…day。 In 1888 Theodore Vail set on foot a second series of experiments； to see if a cable could be made that was better suited as a highway for the delicate electric currents of the telephone。 A young engineer named John A。 Barrett； who had already made his mark as an expert； by finding a way to twist and transpose the wires； was set apart to tackle this problem。 Being an economical Vermonter； Barrett went to work in a little wooden shed in the backyard of a Brooklyn foundry。 In this foundry he had seen a unique machine that could be made to mould hot lead around a rope of twisted wires。 This was a notable discovery。 It meant TIGHT COVERINGS。 It meant a victory over that most troublesome of enemiesmoisture。 Also； it meant that cables could henceforth be made longer； with fewer sleeves and splices； and without the oil； which had always been an unmitigated nuisance。
Next； having made the cable tight； Barrett set out to produce it more cheaply and by accident stumbled upon a way to make it immensely more efficient。 All wires were at that time wrapped with cotton； and his plan was to find some less costly material that would serve the same purpose。 One of his workmen； a Virginian； suggested the use of paper twine； which had been used in the South during the Civil War； when cotton was scarce and expensive。 Barrett at once searched the South for paper twine and found it。 He bought a barrel of it from a small factory in Richmond； but after a trial it proved to be too flimsy。 If such paper could be put on flat； he reasoned； it would be stronger。 Just then he heard of an erratic genius who had an invention for winding paper tape on wire for the use of milliners。
Paper…wound bonnet…wire！ Who could imagine any connection between this and the telephone？ Yet this hint was exactly what Barrett needed。 He experimented until he had devised a machine that crumpled the paper around the wire； instead of winding it tightly。 This was the finishing touch。 For a time these paper…wound cables were soaked in oil； but in 1890 Engineer F。 A。 Pickernell dared to trust to the tightness of the lead sheathing； and laid a 〃dry core〃 cable； the first of the modern type； in one of the streets of Philadelphia。 This cable was the event of the year。 It was not only cheaper。 It was the best…talking cable that had ever been harnessed to a telephone。
What Barrett had done was soon made clear。 By wrapping the wire with loose paper； he had in reality cushioned it with AIR； which is the best possible insulator。 Not the paper； but the air in the paper； had improved the cable。 More air was added by the omission of the oil。 And presently Barrett perceived that he had merely reproduced in a cable； as far as possible； the conditions of the overhead wires； which are separated by nothing but air。
By 1896 there were two hundred thousand miles of wire snugly wrapped in paper and lying in leaden caskets beneath the streets of the cities； and to…day there are six million miles of it owned by the affiliated Bell companies。 Instead of blackening the streets； the wire nerves of the telephone are now out of sight under the roadway； and twining into the basements of buildings like a new sort of metallic ivy。 Some cables are so large that a single spool of cable will weigh twenty…six tons and require a giant truck and a sixteen…horse team to haul it to its resting…place。 As many as twelve hundred wires are often bunched into one sheath； and each cable lies loosely in a little duct of its own。 It is reached by manholes where it runs under the streets and in little switching…boxes placed at intervals it is frayed out into separate pairs of wires that blossom at length into telephones。
Out in the open country there are still the open wires； which in point of talking are the best。 In the suburbs of cities there are neat green posts with a single gray cable hung from a heavy wire。 Usually； a telephone pole is made from a sixty…year…old tree； a cedar； chestnut； or juniper。 It lasts twelve years only； so that the one item of poles is still costing the telephone companies several millions a year。 The total number of poles now in the United States； used by telephone and telegraph companies； once covered an area； before they were cut down； as large as the State of Rhode Island。
But the highest triumph of wire…laying came when New York swept into the Skyscraper Age； and when hundreds of tall buildings； as high as the fall of the waters of Niagara； grew up like a range of magical cliffs upon the precious rock of Manhattan。 Here the work of the telephone engineer has been so well done that although every room in these cliff…buildings has its telephone； there is not a pole in sight； not a cross…arm； not a wire。 Nothing but the tip…ends of an immense system are visible。 No sooner is a new skyscraper walled and roofed； than the telephones are in place； at once putting the tenants in touch with the rest of the city and the greater part of the United States。 In a single one of these monstrous buildings； the Hudson Terminal； there is a cable that runs from basement to roof and ravels out to reach three thousand desks。 This mighty geyser of wires is fifty tons in weight and would； if straightened out into a single line； connect New York with Chicago。 Yet it is as invisible as the nerves and muscles of a human body。
During this evolution of the cable； even the wire itself was being remade。 Vail and others had noticed that of all the varieties of wire that were for sale； not one was exactly suitable for a telephone system。 The first telephone wire was of galvanized iron； which had at least the primitive virtue of being cheap。 Then came steel wire； stronger but less durable。 But these wires were noisy and not good conductors of electricity。 An ideal telephone wire； they found； must be made of either silver or copper。 Silver was out of the question； and copper wire was too soft and weak。 It would not carry its own weight。
The problem； therefore； was either to make steel wire a better conductor； or to produce a copper wire that would be strong enough。 Vail chose the latter； and forthwith gave orders to a Bridgeport manufacturer to begin experiments。 A young expert named Thomas B。 Doolittle was at once set to work； and presently appeared the first hard…drawn copper wire； made tough… skinned by a fairly simple process。 Vail bought thirty pounds of it and scattered it in various parts of the United States； to note the effect upon it of different climates。 One length of it may still be seen at the Vail homestead in Lyndonville； Vermont。 Then this hard…drawn wire was put to a severe test by being strung between Boston and New York。 This line was a brilliant success； and the new wire was hailed with great delight as the ideal servant of the telephone。
Since then there has been little trouble with copper wire； except its price。 It was four times as good as iron wire； and four times as expensive。 Every mile of it； doubled； weighed two hundred pounds and cost thirty dollars。 On the long lines； where it had to be as thick as a lead pencil； the expense seemed to be ruinously great。 When the first pair of wires was strung between New York and Chicago； for instance； it was found to weigh 870；000 poundsa full load for a twenty…two…car freight train； and the cost of the bar
