heroes of the telegraph-第50章

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ted　powers　of　hearing。　　By　these　three　instruments　we　have　thus　received　a　remarkable　extension　of　the　capacity　of　the　human　ear；　and　a　growth　of　dominion　over　the　sounds　of　Nature。　　We　have　now　a　command　over　sound　such　as　we　have　over　light。　　For　the　telephone　is　to　the　ear　what　the　telescope　is　to　the　eye；　the　phonograph　is　for　sound　what　the　photograph　is　for　light；　and　the　microphone　finds　its　analogue　in　the　microscope。　　As　the　microscope　reveals　to　our　wondering　sight　the　rich　meshes　of　creation；　so　the　microphone　can　interpret　to　our　ears　the　jarr　of　molecular　vibrations　for　ever　going　on　around　us；　perchance　the　clash　of　atoms　as　they　shape　themselves　into　crystals；　the　murmurous　ripple　of　the　sap　in　trees；　which　Humboldt　fancied　to　make　a　continuous　music　in　the　ears　of　the　tiniest　insects；　the　fall　of　pollen　dust　on　flowers　and　grasses；　the　stealthy　creeping　of　a　spider　upon　his　silken　web；　and　even　the　piping　of　a　pair　of　love…sick　butterflies；　or　the　trumpeting　of　a　bellicose　gnat；　like　the　'horns　of　elf…land　faintly　blowing。'

The　success　of　the　Hughes　type…printer　may　be　said　to　have　covered　its　author　with　titles　and　scientific　honours；　and　placed　him　above　the　necessity　of　regular　employment。　　He　left　America；　and　travelled　from　place　to　place。　　For　many　years　past；　however；　he　has　resided　privately　in　London；　an　eminent　example　of　that　modesty　and　simplicity　which　is　generally　said　to　accompany　true　genius。

Mechanical　invention　is　influenced　to　a　very　high　degree　by　external　circumstances。　　It　may　sound　sensational；　but　it　is　nevertheless　true；　that　we　owe　the　microphone　to　an　attack　of　bronchitis。　　During　the　thick　foggy　weather　of　November　1877；　Professor　Hughes　was　confined　to　his　home　by　a　severe　cold；　and　in　order　to　divert　his　thoughts　he　began　to　amuse　himself　with　a　speaking　telephone。　　Then　it　occurred　to　him　that　there　might　be　some　means　found　of　making　the　wire　of　the　telephone　circuit　speak　of　itself　without　the　need　of　telephones　at　all；　or　at　least　without　the　need　of　one　telephone；　namely；　that　used　in　transmitting　the　sounds。　　The　distinguished　physicist　Sir　William　Thomson；　had　lately　discovered　the　peculiar　fact　that　when　a　current　of　electricity　is　passed　through　a　wire；　the　current　augments　when　the　wire　is　extended；　and　diminishes　when　the　wire　is　compressed；　because　in　the　former　case　the　resistance　of　the　material　of　the　wire　to　the　passage　of　the　current　is　lessened；　and　in　the　latter　case　it　becomes　greater。

Now　it　occurred　to　Professor　Hughes　that；　if　this　were　so；　it　might　be　possible　to　cause　the　air…vibrations　of　sound　to　so　act　upon　a　wire　conveying　a　current　as　to　stretch　and　contract　it　in　sympathy　with　themselves；　so　that　the　sound…waves　would　create　corresponding　electric　waves　in　the　current；　and　these　electric　waves；　passed　through　a　telephone　connected　to　the　wire；　would　cause　the　telephone　to　give　forth　the　original　sounds。　　He　first　set　about　trying　the　effect　of　vibrating　a　wire　in　which　a　current　flowed；　to　see　if　the　stretching　and　compressing　thereby　produced　would　affect　the　current　so　as　to　cause　sounds　in　a　telephone　connected　up　in　circuit　with　the　wirebut　without　effect。　　He　could　hear　no　sound　whatever　in　the　telephone。　　Then　he　stretched　the　wire　till　it　broke　altogether；　and　as　the　metal　began　to　rupture　he　heard　a　distinct　grating　in　the　telephone；　followed　by　a　sharp　'click；'　when　the　wire　sundered；　which　indicated　a　'rush'　of　electricity　through　the　telephone。　　This　pointed　out　to　him　that　the　wire　might　be　sensitive　to　sound　when　in　a　state　of　fracture。　　Acting　on　the　hint；　he　placed　the　two　broken　ends　of　the　wire　together　again；　and　kept　them　so　by　the　　application　of　a　definite　pressure。　　To　his　joy　he　found　that　he　had　discovered　what　he　had　been　in　search　of。　　The　imperfect　contact　between　the　broken　ends　of　the　wire　proved　itself　to　be　a　means　of　transmitting　sounds；　and　in　addition　it　was　found　to　possess　a　faculty　which　he　had　not　anticipatedit　proved　to　be　sensitive　to　very　minute　sounds；　and　was　in　fact　a　rude　microphone。　Continuing　his　researches；　he　soon　found　that　he　had　discovered　a　prin…　ciple　of　wide　application；　and　that　it　was　not　necessary　to　confine　his　experiments　to　wires；　since　any　substance　which　conducted　an　electric　current　would　answer　the　purpose。　　All　that　was　necessary　was　that　the　materials　employed　should　be　in　contact　with　each　other　under　a　slight　but　definite　pressure；　and；　for　the　continuance　of　the　effects；　that　the　materials　should　not　oxidise　in　air　so　as　to　foul　the　contact。　　For　different　materials　a　different　degree　of　pressure　gives　the　best　results；　and　for　different　sounds　to　be　transmitted　a　different　degree　of　pressure　is　required。　　Any　loose；　crazy　　unstable　structure；　of　conducting　bodies；　inserted　in　a　telephone　circuit；　will　act　as　a　microphone。　　Such；　for　example；　as　a　glass　tube　filled　with　lead…shot　or　black　oxide　of　iron；　or　'white　bronze'　powder　under　pressure；　a　metal　watch…chain　piled　in　a　heap。　　Surfaces　of　platinum；　gold；　or　even　iron；　pressed　lightly　together　give　excellent　results。　　Three　French　nails；　two　parallel　beneath　and　one　laid　across　them；　or　better　still　a　log…　hut　of　French　nails；　make　a　perfect　transmitter　of　audible　sounds；　and　a　good　microphone。　　Because　of　its　cheapness；　its　conducting　power；　and　its　　non…oxidisability；　carbon　is　the　most　select　material。　　A　piece　of　charcoal　no　bigger　than　a　pin's　head　is　quite　sufficient　to　produce　articulate　speech。　　Gas…carbon　operates　admirably；　but　the　best　carbon　is　that　known　as　willow…charcoal；　used　by　artists　in　sketching；　and　when　this　is　impregnated　with　minute　globules　of　mercury　by　heating　it　white…　hot　and　quenching　it　in　liquid　mercury；　it　is　in　a　highly　sensitive　microphonic　condition。　　The　same　kind　of　charcoal　permeated　by　platinum；　tin；　zinc；　or　other　unoxidisable　metal　is　also　very　suitable；　and　it　is　a　significant　fact　that　the　most　resonant　woods；　such　as　pine；　poplar；　and　willow；　yield　the　charcoals　best　adapted　for　the　microphone。　Professor　Hughes'　experimental　apparatus　is　of　an　amusingly　simple　description。　　He　has　no　laboratory　at　home；　and　all　his　experiments　were　made　in　the　drawing…room。　　His　first　microphones　were　formed　of　bits　of　carbon　and　scraps　of　metal；　mounted　on　slips　of　match…boxes　by　means　of　sealing…wax；　and　the　resonance　pipes　on　which　they　were　placed　to　reinforce　the　effect　of　minute　sounds；　were　nothing　more　than　children's　toy　money　boxes；　price　one　halfpenny；　having　one　of　the　ends　knocked　out。　　With　such　childish　and　worthless　materials　he　has　conquered　Nature　in　her　strongholds；　and　shown　how　great　discoveries　can　be　made。　　The　microphone　is　a　striking　illustration　of　the　truth　that　in　science　any　phenomenon　whatever　may　be　rendered　useful。　　The　trouble　of　one　generation　of　scientists　may　be　turned　to　the　honour　and　service　of　the　next。　　Electricians　have　long　had　sore　reasons　for　regarding　a　'bad　contact'　as　an　unmitigated　nuisance；　the　instrument　of　the　evil　one；　with　no　conceivable　good　in　it；　and　no　conceivable　purpose　except　to　annoy　and　tempt　them　into　wickedness　and　an　expression　of　hearty　but　ignominious　emotion。　　Professor　Hughes；　however；　has　with　a　wizard's　power　transformed　this　electrician's　bane　into　a　professional　glory　and　a　public　boon。　Verily　there　is　a　soul　of　virtue　in　things　evil。

The　commonest　and　at　the　same　time　one　of　the　most　sensitive　forms　of　the　instrument　is　called　the　'pencil　microphone；'　from　the　pencil　or　crayon　of　carbon　which　forms　the　principal　part　of　it。　　This　pencil　may　be　of　mercurialised　charcoal；　but　the　ordinary　gas…carbon；　which　incrusts　the　interior　of　the　retorts　in　gas…works；　is　usually　employed。　The　crayon　is　supported　in　an　upright　position　by　two　little　brackets　of　carbon；　hollowed　out　so　as　to　receive　the　pointed　ends　in　shallow　cups。　The　weight　of　the　crayon　suffices　to　give　the　required　pressure　on　the　contacts；　both　upper　and　lower；　for　the　upper　end　of　the　Pencil　should　lean　against　the　inner　wall　of　the　cup　in　the　upper　bracket。　　The　brackets　are　fixed　to　an　upright　board　of　light；　dry；　resonant　pine…　wood；　let　into　a　solid　base　of　the　same　timber。　　The　baseboard　　is　with　advantage　borne　by　four　rounded　india…rubber　　feet；　which　insulate