the age of invention-第24部分

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It　may　startle　some　reader　to　be　told　that　the　foundations　of　modern　electrical　science　were　definitely　established　in　the　Elizabethan　Age。　The　England　of　Elizabeth；　of　Shakespeare；　of　Drake　and　the　sea…dogs；　is　seldom　thought　of　as　the　cradle　of　the　science　of　electricity。　Nevertheless；　it　was；　just　as　surely　as　it　was　the　birthplace　of　the　Shakespearian　drama；　of　the　Authorized　Version　of　the　Bible；　or　of　that　maritime　adventure　and　colonial　enterprise　which　finally　grew　and　blossomed　into　the　United　States　of　America。

The　accredited　father　of　the　science　of　electricity　and　magnetism　is　William　Gilbert；　who　was　a　physician　and　man　of　learning　at　the　court　of　Elizabeth。　Prior　to　him；　all　that　was　known　of　these　phenomena　was　what　the　ancients　knew；　that　the　lodestone　possessed　magnetic　properties　and　that　amber　and　jet；　when　rubbed；　would　attract　bits　of　paper　or　other　substances　of　small　specific　gravity。　Gilbert's　great　treatise　〃On　the　Magnet〃；　printed　in　Latin　in　1600；　containing　the　fruits　of　his　researches　and　experiments　for　many　years；　indeed　provided　the　basis　for　a　new　science。

On　foundations　well　and　truly　laid　by　Gilbert　several　Europeans；　like　Otto　von　Guericke　of　Germany；　Du　Fay　of　France；　and　Stephen　Gray　of　England；　worked　before　Benjamin　Franklin　and　added　to　the　structure　of　electrical　knowledge。　The　Leyden　jar；　in　which　the　mysterious　force　could　be　stored；　was　invented　in　Holland　in　1745　and　in　Germany　almost　simultaneously。

Franklin's　important　discoveries　are　outlined　in　the　first　chapter　of　this　book。　He　found　out；　as　we　have　seen；　that　electricity　and　lightning　are　one　and　the　same；　and　in　the　lightning　rod　he　made　the　first　practical　application　of　electricity。　Afterwards　Cavendish　of　England；　Coulomb　of　France；　Galvani　of　Italy；　all　brought　new　bricks　to　the　pile。　Following　them　came　a　group　of　master　builders；　among　whom　may　be　mentioned：　Volta　of　Italy；　Oersted　of　Denmark；　Ampere　of　France；　Ohm　of　Germany；　Faraday　of　England；　and　Joseph　Henry　of　America。

Among　these　men；　who　were；　it　should　be　noted；　theoretical　investigators；　rather　than　practical　inventors　like　Morse；　or　Bell；　or　Edison；　the　American　Joseph　Henry　ranks　high。　Henry　was　born　at　Albany　in　1799　and　was　educated　at　the　Albany　Academy。　Intending　to　practice　medicine；　he　studied　the　natural　sciences。　He　was　poor　and　earned　his　daily　bread　by　private　tutoring。　He　was　an　industrious　and　brilliant　student　and　soon　gave　evidence　of　being　endowed　with　a　powerful　mind。　He　was　appointed　in　1824　an　assistant　engineer　for　the　survey　of　a　route　for　a　State　road；　three　hundred　miles　long；　between　the　Hudson　River　and　Lake　Erie。　The　experience　he　gained　in　this　work　changed　the　course　of　his　career；　he　decided　to　follow　civil　and　mechanical　engineering　instead　of　medicine。　Then　in　1826　he　became　teacher　of　mathematics　and　natural　philosophy　in　the　Albany　Academy。

It　was　in　the　Albany　Academy　that　he　began　that　wide　series　of　experiments　and　investigations　which　touched　so　many　phases　of　the　great　problem　of　electricity。　His　first　discovery　was　that　a　magnet　could　be　immensely　strengthened　by　winding　it　with　insulated　wire。　He　was　the　first　to　employ　insulated　wire　wound　as　on　a　spool　and　was　able　finally　to　make　a　magnet　which　would　lift　thirty…five　hundred　pounds。　He　first　showed　the　difference　between　〃quantity〃　magnets　composed　of　short　lengths　of　wire　connected　in　parallel；　excited　by　a　few　large　cells；　and　〃intensity〃　magnets　wound　with　a　single　long　wire　and　excited　by　a　battery　composed　of　cells　in　series。　This　was　an　original　discovery；　greatly　increasing　both　the　immediate　usefulness　of　the　magnet　and　its　possibilities　for　future　experiments。

The　learned　men　of　Europe；　Faraday；　Sturgeon；　and　the　rest；　were　quick　to　recognize　the　value　of　the　discoveries　of　the　young　Albany　schoolmaster。　Sturgeon　magnanimously　said：　〃Professor　Henry　has　been　enabled　to　produce　a　magnetic　force　which　totally　eclipses　every　other　in　the　whole　annals　of　magnetism；　and　no　parallel　is　to　be　found　since　the　miraculous　suspension　of　the　celebrated　Oriental　imposter　in　his　iron　coffin。〃*

*　Philosophical　Magazine；　vol。　XI；　p。　199　（March；　1832）。


Henry　also　discovered　the　phenomena　of　self　induction　and　mutual　induction。　A　current　sent　through　a　wire　in　the　second　story　of　the　building　induced　currents　through　a　similar　wire　in　the　cellar　two　floors　below。　In　this　discovery　Henry　anticipated　Faraday　though　his　results　as　to　mutual　induction　were　not　published　until　he　had　heard　rumors　of　Faraday's　discovery；　which　he　thought　to　be　something　different。

The　attempt　to　send　signals　by　electricity　had　been　made　many　times　before　Henry　became　interested　in　the　problem。　On　the　invention　of　Sturgeon's　magnet　there　had　been　hopes　in　England　of　a　successful　solution；　but　in　the　experiments　that　followed　the　current　became　so　weak　after　a　few　hundred　feet　that　the　idea　was　pronounced　impracticable。　Henry　strung　a　mile　of　fine　wire　in　the　Academy；　placed　an　〃intensity〃　battery　at　one　end；　and　made　the　armature　strike　a　bell　at　the　other。　Thus　he　discovered　the　essential　principle　of　the　electric　telegraph。　This　discovery　was　made　in　1831；　the　year　before　the　idea　of　a　working　electric　telegraph　flashed　on　the　mind　of　Morse。　There　was　no　occasion　for　the　controversy　which　took　place　later　as　to　who　invented　the　telegraph。　That　was　Morse's　achievement；　but　the　discovery　of　the　great　fact；　which　startled　Morse　into　activity；　was　Henry's　achievement。　In　Henry's　own　words：　〃This　was　the　first　discovery　of　the　fact　that　a　galvanic　current　could　be　transmitted　to　a　great　distance　with　so　little　a　diminution　of　force　as　to　produce　mechanical　effects；　and　of　the　means　by　which　the　transmission　could　be　accomplished。　I　saw　that　the　electric　telegraph　was　now　practicable。〃　He　says　further；　however：　〃I　had　not　in　mind　any　particular　form　of　telegraph；　but　referred　only　to　the　general　fact　that　it　was　now　demonstrated　that　a　galvanic　current　could　be　transmitted　to　great　distances；　with　sufficient　power　to　produce　mechanical　effects　adequate　to　the　desired　object。〃*

*　Deposition　of　Joseph　Henry；　September　7；　1849；　printed　in　Morse；　〃The　Electra…Magnetic　Telegraph〃；　p。　91。


Henry　next　turned　to　the　possibility　of　a　magnetic　engine　for　the　production　of　power　and　succeeded　in　making　a　reciprocating…bar　motor；　on　which　he　installed　the　first　automatic　pole　changer；　or　commutator；　ever　used　with　an　electric　battery。　He　did　not　succeed　in　producing　direct　rotary　motion。　His　bar　oscillated　like　the　walking　beam　of　a　steamboat。

Henry　was　appointed　in　1839。　Professor　of　Natural　Philosophy　in　the　College　of　New　Jersey；　better　known　today　as　Princeton　University。　There　he　repeated　his　old　experiments　on　a　larger　scale；　confirmed　Steinheil's　experiment　of　using　the　earth　as　return　conductor；　showed　how　a　feeble　current　would　be　strengthened；　and　how　a　small　magnet　could　be　used　as　a　circuit　maker　and　breaker。　Here　were　the　principles　of　the　telegraph　relay　and　the　dynamo。

Why；　then；　if　the　work　of　Henry　was　so　important；　is　his　name　almost　forgotten；　except　by　men　of　science；　and　not　given　to　any　one　of　the　practical　applications　of　electricity？　The　answer　is　plain。　Henry　was　an　investigator；　not　an　inventor。　He　states　his　position　very　clearly：　〃I　never　myself　attempted　to　reduce　the　principles　to　practice；　or　to　apply　any　of　my　discoveries　to　processes　in　the　arts。　My　whole　attention　exclusive　of　my　duties　to　the　College；　was　devoted　to　original　scientific　investigations；　and　I　left　to　others　what　I　considered　in　a　scientific　view　of　subordinate　importancethe　application　of　my　discoveries　to　useful　purposes　in　the　arts。　Besides　this　I　partook　of　the　feeling　common　to　men　of　science；　which　disinclines　them　to　secure　to　themselves　the　advantages　of　their　discoveries　by　a　patent。〃

Then；　too；　his　talents　were　soon　turned　to　a　wider　field。　The　bequest　of　James　Smithson；　that　farsighted　Englishman；　who　left　his　fortune　to　the　United　States　to　found　〃the　Smithsonian　Institution；　for　the　increase　and　diffusion　of　knowledge　among　men；〃　was　responsible　for　the　diffusion　of　Henry's　activities。　The　Smithsonian　Institution　was　founded　at　Washington　in　1846；　and　Henry　was　fittingly　chosen　its　Secretary；　that　is；　its　chief　executive　officer。　And　from　that　time　until　his　death　in　1878；　over　thirty　years；　he　devoted　himself　to　science　in　general。

He　studied　terrestrial　magnetism　and　building　materials。　He　reduced　meteorology　to　a　science；　collecting　reports　by　telegraph；　made　the　first　weather　map；　and　issued　forecasts　of　the　weather　based　upon　definite　knowledge　rather　than　upon　signs。　He　became　a　member　of　the　Lighthouse　Board　in　1852　and　was　the　head　after　1871。　The　excellence　of　marine　illuminants　and　fog　signals　today　is　largely　due　to　his　efforts。　Though　he　was　later　drawn　into　a　controversy　with　Morse　over　the　credit　for　the　invention　of　the　telegraph；　he　used　his　influence　to　procure　the　renewal　of　Morse's　patent。　He　listened　with　attention　to　Alexander　Graham　Bell；　who　had　the　idea　that　electric　wires　might　be　made　to　carry　the　human　voice；　and　encouraged　him　to　proceed　with　his　experiments。　〃He　said；〃　Bell　writes；　〃that　he　thought　it　was　the　germ　of　a　great　invention　and　advised　me　to　work　at　it　without　publishing。　I　said　that　I　recognized　the　fact　that　there　were　mechanical　difficulties　in　the　way　that　rendered　the　plan　impracticable　at　the　present　time。　I　added　that　I　felt　that　I　had　not　the　electrical　knowledge　necessary　to　overcome　the　difficulties。　His　laconic　answer　was；　'GET　IT！'　I　cannot　tell　you　how　much　these　two　words　have　encouraged　me。〃

Henry　had　blazed　the　way　for　others　to　work　out　the　principles　of　the　electric　motor；　and　a　few　experimenters　attempted　to　follow　his　lead。　Thomas　Davenport；　a　blacksmith　of　Brandon；　Vermont；　built　an　electric　car　in　1835；　which　he　was　able　to　drive　on　the　road；　and　so　made　himself　the　pioneer　of　the　automobile　in　America。　Twelve　years　later　Moses　G。　Farmer　exhibited　at　various　places　in　New　England　an　electric…driven　locomotive；　and　in　1851　Charles　Grafton　Page　drove　an　electric　car；　on　the　tracks　of　the　Baltimore　and　Ohio　Railroad；　from　Washington　to　Bladensburg；　at　the　rate　of　nineteen　miles　an　hour。　But　the　cost　of　batter