heroes of the telegraph-第4章

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und　conductors；　like　to　gas　in　pipes。　'And　if　music　be　capable　of　being　thus　conducted；'　he　observes；'perhaps　the　words　of　speech　may　be　susceptible　of　the　same　means　of　propagation。　The　eloquence　of　counsel；　the　debates　of　Parliament；　instead　of　being　read　the　next　day　only；But　we　shall　lose　ourselves　in　the　pursuit　of　this　curious　subject。'

Besides　transmitting　sounds　to　a　distance；　Wheatstone　devised　a　simple　instrument　for　augmenting　feeble　sounds；　to　which　he　gave　the　name　of　'Microphone。'　It　consisted　of　two　slender　rods；　which　conveyed　the　mechanical　vibrations　to　both　ears；　and　is　quite　different　from　the　electrical　microphone　of　Professor　Hughes。

In　1823；　his　uncle；　the　musical　instrument　maker；　died；　and　Wheatstone；　with　his　elder　brother；　William；　took　over　the　business。　Charles　had　no　great　liking　for　the　commercial　part；　but　his　ingenuity　found　a　vent　in　making　improvements　on　the　existing　instruments；　and　in　devising　philosophical　toys。　　At　the　end　of　six　years　he　retired　from　the　undertaking。

In　1827；　Wheatstone　introduced　his　'kaleidoscope；'　a　device　for　rendering　the　vibrations　of　a　sounding　body　apparent　to　the　eye。　　It　consists　of　a　metal　rod；　carrying　at　its　end　a　silvered　bead；　which　reflects　a　'spot'　of　light。　　As　the　rod　vibrates　the　spot　is　seen　to　describe　complicated　figures　in　the　air；　like　a　spark　whirled　about　in　the　darkness。　　His　photometer　was　probably　suggested　by　this　appliance。　It　enables　two　lights　to　be　compared　by　the　relative　brightness　of　their　reflections　in　a　silvered　bead；　which　describes　a　narrow　ellipse；　so　as　to　draw　the　spots　into　parallel　lines。

In　1828；　Wheatstone　improved　the　German　wind　instrument；　called　the　MUND　HARMONICA；　till　it　became　the　popular　concertina；　patented　on　June　19；　1829　The　portable　harmonium　is　another　of　his　inventions；　which　gained　a　prize　medal　at　the　Great　Exhibition　of　1851。　　He　also　improved　the　speaking　machine　of　De　Kempelen；　and　endorsed　the　opinion　of　Sir　David　Brewster；　that　before　the　end　of　this　century　a　singing　and　talking　apparatus　would　be　among　the　conquests　of　science。

In　1834；　Wheatstone；　who　had　won　a　name　for　himself；　was　appointed　to　the　Chair　of　Experimental　Physics　in　King's　College；　London；　But　his　first　course　of　lectures　on　Sound　were　a　complete　failure；　owing　to　an　invincible　repugnance　to　public　speaking；　and　a　distrust　of　his　powers　in　that　direction。　　In　the　rostrum　he　was　tongue…tied　and　incapable；　sometimes　turning　his　back　on　the　audience　and　mumbling　to　the　diagrams　on　the　wall。　　In　the　laboratory　he　felt　himself　at　home；　and　ever　after　confined　his　duties　mostly　to　demonstration。

He　achieved　renown　by　a　great　experimentthe　measurement　of　the　velocity　of　electricity　in　a　wire。　　His　method　was　beautiful　and　ingenious。　　He　cut　the　wire　at　the　middle；　to　form　a　gap　which　a　spark　might　leap　across；　and　connected　its　ends　to　the　poles　of　a　Leyden　jar　filled　with　electricity。　　Three　sparks　were　thus　produced；　one　at　either　end　of　the　wire；　and　another　at　the　middle。　　He　mounted　a　tiny　mirror　on　the　works　of　a　watch；　so　that　it　revolved　at　a　high　velocity；　and　observed　the　reflections　of　his　three　sparks　in　it。　　The　points　of　the　wire　were　so　arranged　that　if　the　sparks　were　instantaneous；　their　reflections　would　appear　in　one　straight　line；　but　the　middle　one　was　seen　to　lag　behind　the　others；　because　it　was　an　instant　later。　　The　electricity　had　taken　a　certain　time　to　travel　from　the　ends　of　the　wire　to　the　middle。　　This　time　was　found　by　measuring　the　amount　of　lag；　and　comparing　it　with　the　known　velocity　of　the　mirror。　　Having　got　the　time；　he　had　only　to　compare　that　with　the　length　of　half　the　wire；　and　he　found　that　the　velocity　of　electricity　was　288；000　miles　a　second。

Till　then；　many　people　had　considered　the　electric　discharge　to　be　instantaneous；　but　it　was　afterwards　found　that　its　velocity　depended　on　the　nature　of　the　conductor；　its　resistance；　and　its　electro…static　capacity。　　Faraday　showed；　for　example；　that　its　velocity　in　a　submarine　wire；　coated　with　insulator　and　surrounded　with　water；　is　only　144；000　miles　a　second；　or　still　less。　　Wheatstone's　device　of　the　revolving　mirror　was　afterwards　employed　by　Foucault　and　Fizeau　to　measure　the　velocity　of　light。

In　1835；　at　the　Dublin　meeting　of　the　British　Association；　Wheatstone　showed　that　when　metals　were　volatilised　in　the　electric　spark；　their　light；　examined　through　a　prism；　revealed　certain　rays　which　were　characteristic　of　them。　　Thus　the　kind　of　metals　which　formed　the　sparking　points　could　be　determined　by　analysing　the　light　of　the　spark。　This　suggestion　has　been　of　great　service　in　spectrum　analysis；　and　as　applied　by　Bunsen；　Kirchoff；　and　others；　has　led　to　the　discovery　of　several　new　elements；　such　as　rubidium　and　thallium；　as　well　as　increasing　our　knowledge　of　the　heavenly　bodies。　　Two　years　later；　he　called　attention　to　the　value　of　thermo…electricity　as　a　mode　of　generating　a　current　by　means　of　heat；　and　since　then　a　variety　of　thermo…piles　have　been　invented；　some　of　which　have　proved　of　considerable　advantage。

Wheatstone　abandoned　his　idea　of　transmitting　intelligence　by　the　mechanical　vibration　of　rods；　and　took　up　the　electric　telegraph。　　In　1835　he　lectured　on　the　system　of　Baron　Schilling；　and　declared　that　the　means　were　already　known　by　which　an　electric　telegraph　could　be　made　of　great　service　to　the　world。　　He　made　experiments　with　a　plan　of　his　own；　and　not　only　proposed　to　lay　an　experimental　line　across　the　Thames；　but　to　establish　it　on　the　London　and　Birmingham　Railway。　　Before　these　plans　were　carried　out；　however；　he　received　a　visit　from　Mr。　Fothergill　Cooke　at　his　house　in　Conduit　Street　on　February　27；　1837；　which　had　an　important　influence　on　his　future。

Mr。　Cooke　was　an　officer　in　the　Madras　army；　who；　being　home　on　furlough；　was　attending　some　lectures　on　anatomy　at　the　University　of　Heidelberg；　where；　on　March　6；　1836；　he　witnessed　a　demonstration　with　the　telegraph　of　Professor　Moncke；　and　was　so　impressed　with　its　importance；　that　he　forsook　his　medical　studies　and　devoted　all　his　efforts　to　the　work　of　introducing　the　telegraph。　　He　returned　to　London　soon　after；　and　was　able　to　exhibit　a　telegraph　with　three　needles　in　January；　1837。　　Feeling　his　want　of　scientific　knowledge；　he　consulted　Faraday　and　Dr。　Roget；　the　latter　of　whom　sent　him　to　Wheatstone。

At　a　second　interview；　Mr。　Cooke　told　Wheatstone　of　his　intention　to　bring　out　a　working　telegraph；　and　explained　his　method。　　Wheatstone；　according　to　his　own　statement；　remarked　to　Cooke　that　the　method　would　not　act；　and　produced　his　own　experimental　telegraph。　　Finally；　Cooke　proposed　that　they　should　enter　into　a　partnership；　but　Wheatstone　was　at　first　reluctant　to　comply。　　He　was　a　well…known　man　of　science；　and　had　meant　to　publish　his　results　without　seeking　to　make　capital　of　them。　　Cooke；　on　the　other　hand；　declared　that　his　sole　object　was　to　make　a　fortune　from　the　scheme。　　In　May　they　agreed　to　join　their　forces；　Wheatstone　contributing　the　scientific；　and　Cooke　the　administrative　talent。　　The　deed　of　partnership　was　dated　November　19；　1837。　　A　joint　patent　was　taken　out　for　their　inventions；　including　the　five…needle　telegraph　of　Wheatstone；　and　an　alarm　worked　by　a　relay；　in　which　the　current；　by　dipping　a　needle　into　mercury；　completed　a　local　circuit；　and　released　the　detent　of　a　clockwork。

The　five…needle　telegraph；　which　was　mainly；　if　not　entirely；　due　to　Wheatstone；　was　similar　to　that　of　Schilling；　and　based　on　the　principle　enunciated　by　Amperethat　is　to　say；　the　current　was　sent　into　the　line　by　completing　the　circuit　of　the　battery　with　a　make　and　break　key；　and　at　the　other　end　it　passed　through　a　coil　of　wire　surrounding　a　magnetic　needle　free　to　turn　round　its　centre。　　According　as　one　pole　of　the　battery　or　the　other　was　applied　to　the　line　by　means　of　the　key；　the　current　deflected　the　needle　to　one　side　or　the　other。　　There　were　five　separate　circuits　actuating　five　different　needles。　　The　latter　were　pivoted　in　rows　across　the　middle　of　a　dial　shaped　like　a　diamond；　and　having　the　letters　of　the　alphabet　arranged　upon　it　in　such　a　way　that　a　letter　was　literally　pointed　out　by　the　current　deflecting　two　o