heroes of the telegraph-第41部分

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e　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；　for　the　microphone；　pure　and　simple；　was　operated　by　the　direct　impact　of　the　sonorous　waves；　and　required　no　tympanum。　　Moreover；　the　　microphone；　as　its　name　implies；　could　magnify　a　feeble　sound；　and　render　audible　the　vibrations　which　would　otherwise　escape　the　ear。　　The　discovery　of　these　remarkable　and　subtle　properties　of　a　delicate　contact　had　indeed　confronted　Edison；　he　had　held　them　in　his　grasp；　they　had　stared　him　in　the　face；　but　not…withstanding　all　his　matchless　ingenuity　and　acumen；　he；　blinded　perhaps　by　a　false　hypothesis；　entirely　failed　to　discern　them。　　The　significant　proof　of　it　lies　in　the　fact　that　after　the　researches　of　Professor　Hughes　were　published　the　carbon　transmitter　was　promptly　modified；　and　finally　abandoned　for　practical　work　as　a　telephone；　in　favour　of　a　variety　of　new　transmitters；　such　as　the　Blake；　now　employed　in　the　United　Kingdom；　in　all　of　which　the　essential　part　is　a　microphone　of　hard　carbon　and　metal。　　The　button　of　soot　has　vanished　into　the　limbo　of　superseded　inventions。

Science　appears　to　show　that　every　physical　process　is　reciprocal；　and　may　be　reversed。　　With　this　　principle　in　our　minds；　we　need　not　be　surprised　that　the　microphone　should　not　only　act　as　a　TRANSMITTER　of　sounds；　but　that　it　should　also　act　as　a　RECEIVER。　　Mr。　James　Blyth；　of　Edinburgh；　was　the　first　to　announce　that　he　had　heard　sounds　and　even　speech　given　out　by　a　microphone　itself　when　substituted　for　the　telephone。　　His　transmitting　microphone　and　his　receiving　one　were　simply　jelly…cans　filled　with　cinders　from　the　grate。　　It　then　transpired　that　Professor　Hughes　had　previously　obtained　the　same　remarkable　effects　from　his　ordinary　'pencil'　microphones。　　The　sounds　were　extremely　feeble；　however；　but　the　transmitting　microphones　proved　the　best　articulating　ones。　　Professor　Hughes　at　length　constructed　an　adjustable　　hammer…and…anvil　microphone　of　gas…carbon；　fixed　to　the　top　of　a　resonating　drum；　which　articulated　fairly　well；　although　not　so　perfectly　as　a　Bell　telephone。　　Perhaps　a　means　of　improving　both　the　volume　and　distinctness　　of　the　articulation　will　yet　be　forthcoming　and　we　may　be　able　to　speak　solely　by　the　microphone；　if　it　is　found　desirable。　　The　marvellous　fact　that　a　little　piece　of　charcoal　can；　as　it　were；　both　listen　and　speak；　that　a　person　may　talk　to　it　so　that　his　friend　can　hear　him　at　a　similar　piece　a　hundred　miles　away；　is　a　miracle　of　nineteenth　century　science　which　far　transcends　the　oracles　of　antiquity。

The　articulating　telephone　was　the　forerunner　of　the　phonograph　and　microphone；　and　led　to　their　discovery。　　They　in　turn　will　doubtless　lead　to　other　new　inventions；　which　it　is　now　impossible　to　foresee。　We　ask　in　vain　for　an　answer　to　the　question　which　is　upon　the　lips　of　every　one…What　next？　The　　microphone　has　proved　itself　highly　useful　in　strengthening　the　sounds　given　out　by　the　telephone；　and　it　is　probable　that　we　shall　soon　see　those　three　inventions　working　unitedly；　for　the　microphone　might　make　the　telephone　sounds　so　powerful　as　to　enable　them　to　be　printed　by　phonograph　as　they　are　received；　and　thus　a　durable　record　of　telephonic　messages　would　be　obtained。　　We　can　now　transmit　sound　by　wire；　but　it　may　yet　be　possible　to　transmit　light；　and　see　by　telegraph。　　We　are　apparently　on　the　eve　of　other　wonderful　inventions；　and　there　are　symptoms　that　before　many　years　a　great　fundamental　discovery　will　be　made；　which　will　elucidate　the　connection　of　all　the　physical　forces；　and　will　illumine　the　very　frame…work　of　Nature。

In　1879；　Professor　Hughes　endowed　the　scientific　world　with　another　beautiful　apparatus；　his　'induction　balance。'　　Briefly　described；　it　is　an　arrangement　of　coils　whereby　the　currents　inducted　by　a　primary　circuit　in　the　secondary　are　opposed　to　each　other　until　they　balance；　so　that　a　telephone　connected　in　the　secondary　circuit　is　quite　silent。　Any　disturbance　of　this　delicate　balance；　however；　say　by　the　movement　of　a　coil　or　a　metallic　body　in　the　neighbourhood　of　the　apparatus；　will　be　at　once　reported　by　the　induction　currents　in　the　telephone。　　Being　sensitive　to　the　presence　of　minute　masses　of　metal；　the　apparatus　was　applied　by　Professor　Graham　Bell　to　indicate　the　whereabouts　of　the　missing　bullet　in　the　frame　of　President　Garfield；　as　already　mentioned；　and　also　by　Captain　McEvoy　to　detect　the　position　of　submerged　torpedoes　or　lost　anchors。　　Professor　Roberts…Austen；　the　Chemist　to　the　Mint；　has　also　employed　it　with　success　in　analysing　the　purity　and　temper　of　coins；　for；　strange　to　say；　the　induction　is　affected　as　well　by　the　molecular　quality　as　the　quantity　of　the　disturbing　metal。　Professor　Hughes　himself　has　modified　it　for　the　purpose　of　sonometry；　and　the　measurement　of　the　hearing　powers。

To　the　same　year；　1879；　belong　his　laborious　investigations　on　current　induction；　and　some　ingenious　plans　for　eliminating　its　effects　on　telegraph　and　telephone　circuits。

Soon　after　his　discovery　of　the　microphone　he　was　invited　to　become　a　Fellow　of　the　Royal　Society；　and　a　few　years　later；　in　1885　he　re