heroes of the telegraph-第45部分

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ng　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　it　from　the　table　on　which　it　may　be　placed。　　To　connect　the　microphone　up　for　use；　a　small　voltaic　battery；　say　three　cells　（though　a　single　cell　will　give　surprising　results）；　and　a　Bell　speaking　telephone　are　necessary。　　A　wire　is　led　from　one　of　the　carbon　brackets　to　one　pole　of　the　battery；　and　another　wire　is　led　from　the　other　bracket　to　one　terminal　screw　of　the　telephone；　and　the　circuit　is　completed　by　a　wire　from　the　other　terminal　of　the　telephone　to　the　other　pole　of　the　battery。　　If　now　the　slightest　mechanical　jar　be　given　to　the　wooden　frame　of　the　microphone；　to　the　table；　or　even　to　the　walls　of　the　room　in　which　the　experiment　takes　place；　a　corresponding　noise　will　be　heard　in　the　microphone。　　By　this　delicate　arrangement　we　can　play　the　eavesdropper　on　those　insensible　vibrations　in　the　midst　of　which　we　exist。　　If　a　feather　or　a　camel…hair　pencil　be　stroked　along　the　base…　board；　we　hear　a　harsh　grating　sound；　if　a　pin　be　laid　upon　it；　we　hear　a　blow　like　a　blacksmith's　hammer；　and；　more　astonishing　than　all；　if　a　fly　walk　across　it　we　hear　it　tramping　like　a　charger；　and　even　its　peculiar　cry；　which　has　been　likened；　with　some　allowance　for　imagination；　to　the　snorting　of　an　elephant。　　Moreover　it　should　not　be　forgotten　that　the　wires　connecting　up　the　telephone　may　be　lengthened　to　any　desired　extent；　so　that；　in　the　words　of　Professor　Hughes；　'the　beating　of　a　pulse；　the　tick　of　a　watch；　the　tramp　of　a　fly　can　then　be　heard　at　least　a　hundred　miles　from　the　source　of　sound。'　If　we　whisper　or　speak　distinctly　in　a　monotone　to　the　pencil；　our　words　will　be　heard　in　the　telephone；　but　with　this　defect；　that　the　TIMBRE　or　quality　is；　in　this　particular　form　of　the　instrument；　apt　to　be　lost；　making　it　difficult　to　recognise　the　speaker's　voice。　　But　although　a　single　pencil　microphone　will　under　favourable　circumstances　transmit　these　varied　sounds；　the　best　effect　for　each　kind　of　sound　is　obtained　by　one　specially　adjusted。　There　is　one　pressure　best　adapted　for　minute　sounds；　another　for　speech；　and　a　third　for　louder　sounds。　　A　simple　spring　arrangement　for　adjusting　the　pressure　of　the　contacts　is　therefore　an　advantage；　and　it　can　easily　be　applied　to　a　microphone　formed　of　a　small　rod　of　carbon　pivoted　at　its　middle；　with　one　end　resting　on　a　block　or　anvil　of　carbon　underneath。　The　contact　between　the　rod　and　the　block　in　this　'hammer…and…anvil'　form　is；　of　course；　the　portion　which　is　sensitive　to　sound。

The　microphone　is　a　discovery　as　well　as　an　invention；　and　the　true　explanation　of　its　action　is　as　yet　merely　an　hypothesis。　　It　is　supposed　that　the　vibrations　put　the　carbons　in　a　tremor　and　cause　them　to　approach　more　or　less　nearly；　thus　closing　or　opening　the　breach　between　them；　which　is；　as　it　were；　the　floodgate　of　the　current。

The　applications　of　the　microphone　were　soon　of　great　importance。　　Dr。　B。　W。　Richardson　succeeded　in　fitting　it　for　auscultation　of　the　heart　and　lungs；　while　Sir　Henry　Thompson　has　effectively　used　it　in　those　surgical　operations；　such　as　probing　wounds　for　bullets　or　fragments　of　bone；　in　which　the　surgeon　has　hitherto　relied　entirely　on　his　delicacy　of　touch　for　detecting　the　jar　of　the　probe　on　the　foreign　body。　There　can　be　no　doubt　that　in　the　science　of　physiology；　in　the　art　of　surgery；　and　in　many　other　walks　of　life；　the　microphone　has　proved　a　valuable　aid。

Professor　Hughes　communicated　his　results　to　the　Royal　Society　in　the　early　part　of　1878；　and　generously　gave　the　microphone　to　the　world。　For　his　own　sake　it　would　perhaps　have　been　better　had　he　patented　and　thus　protected　it；　for　Mr。　Edison；　recognising　it　as　a　rival　to　his　carbon…transmitter；　then　a　valuable　property；　claimed　it　as　an　infringement　of　his　patents　and　charged　him　with　plagiarism。　　A　spirited　controversy　arose；　and　several　bitter　lawsuits　were　the　consequence；　in　none　of　which；　however；　Professor　Hughes　took　part；　as　they　were　only　commercial　trials。　　It　was　clearly　shown　that　Clerac；　and　not　Edison；　had　been　the　first　to　utilise　the　variable　resistance　of　powdered　carbon　or　plumbage　under　pressure；　a　property　on　which　the　Edison　transmitter　was　founded；　and　that　Hughes　had　discovered　a　much　wider　principle；　which　embraced　not　only　the　so…called　'semi…conducting'　bodies；　such　as　carbon；　but　even　the　best　conductors；　such　as　gold；　silver；　and　other　metals。　　This　principle　was　not　a　mere　variation　of　electrical　conductivity　in　a　mass　of　material　brought　about　by　compression；　but　a　mysterious　variation　in　some　unknown　way　of　the　strength　of　an　electric　current　in　traversing　a　loose　joint　or　contact　between　two　conductors。　　This　discovery　of　Hughes　really　shed　a　light　on　the　behaviour　of　Edison's　own　transmitter；　whose　action　he　had　until　then　misunderstood。　　It　was　now　seen　that　the　particles　of　carbon　dust　in　contact　which　formed　the　button　were　a　congeries　of　minute　micro…　phones。　　Again　it　was　proved　that　the　diaphragm　or　tympanum　to　receive　the　impression　of　the　sound　and　convey　it　to　the　carbon　button；　on　which　Edison　had　laid　considerable　stress；　was　　non…essential；