the age of invention-第27节

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！



*　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　batteries　was　too　great　and　the　use　of　the　electric　motor　in　transportation　not　yet　practicable。

The　great　principle　of　the　dynamo；　or　electric　generator；　was　discovered　by　Faraday　and　Henry　but　the　process　of　its　development　into　an　agency　of　practical　power　consumed　many　years；　and　without　the　dynamo　for　the　generation　of　power　the　electric　motor　had　to　stand　still　and　there　could　be　no　practicable　application　of　electricity　to　transportation；　or　manufacturing；　or　lighting。　So　it　was　that；　except　for　the　telegraph；　whose　story　is　told　in　another　chapter；　there　was　little　more　American　achievement　in　electricity　until　after　the　Civil　War。

The　arc　light　as　a　practical　illuminating　device　came　in　1878。　It　was　introduced　by　Charles　F。　Brush；　a　young　Ohio　engineer　and　graduate　of　the　University　of　Michigan。　Others　before　him　had　attacked　the　problem　of　electric　lighting；　but　lack　of　suitable　carbons　stood　in　the　way　of　their　success。　Brush　overcame　the　chief　difficulties　and　made　several　lamps　to　burn　in　series　from　one　dynamo。　The　first　Brush　lights　used　for　street　illumination　were　erected　in　Cleveland；　Ohio；　and　soon　the　use　of　arc　lights　became　general。　Other　inventors　improved　the　apparatus；　but　still　there　were　drawbacks。　For　outdoor　lighting　and　for　large　halls　they　served　the　purpose；　but　they　could　not　be　used　in　small　rooms。　Besides；　they　were　in　series；　that　is；　the　current　passed　through　every　lamp　in　turn；　and　an　accident　to　one　threw　the　whole　series　out　of　action。　The　whole　problem　of　indoor　lighting　was　to　be　solved　by　one　of　America's　most　famous　inventors。

The　antecedents　of　Thomas　Alva　Edison　in　America　may　be　traced　back　to　the　time　when　Franklin　was　beginning　his　career　as　a　printer　in　Philadelphia。　The　first　American　Edisons　appear　to　have　come　from　Holland　about　1730　and　settled　on　the　Passaic　River　in　New　Jersey。　Edison's　grandfather；　John　Edison；　was　a　Loyalist　in　the　Revolution　who　found　refuge　in　Nova　Scotia　and　subsequently　moved　to　Upper　Canada。　His　son；　Samuel　Edison；　thought　he　saw　a　moral　in　the　old　man's　exile。　His　father　had　taken　the　King's　side　and　had　lost　his　home；　Samuel　would　make　no　such　error。　So；　when　the　Canadian　Rebellion　of　1837　broke　out；　Samuel　Edison；　aged　thirty…three；　arrayed　himself　on　the　side　of　the　insurgents。　This　time；　however；　the　insurgents　lost；　and　Samuel　was　obliged　to　flee　to　the　United　States；　just　as　his　father　had　fled　to　Canada。　He　finally　settled　at　Milan；　Ohio；　and　there；　in　1847；　in　a　little　brick　house；　which　is　still　standing；　Thomas　Alva　Edison　was　born。

When　the　boy　was　seven　the　family　moved　to　Port　Huron；　Michigan。　The　fact　that　he　attended　school　only　three　months　and　soon　became　self…supporting　was　not　due　to　poverty。　His　mother；　an　educated　woman　of　Scotch　extraction；　taught　him　at　home　after　the　schoolmaster　reported　that　he　was　〃addled。〃　His　desire　for　money　to　spend　on　chemicals　for　a　laboratory　which　he　had　fitted　up　in　the　cellar　led　to　his　first　venture　in　business。　〃By　a　great　amount　of　persistence；〃　he　says；　〃I　got　permission　to　go　on　the　local　train　as　newsboy。　The　local　train