a history of science-2-第51章

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lly　demonstrated　to　his　own　and　the　world's　satisfaction　that　his　theory　was　correct。　Taking　his　kite　out　into　an　open　common　on　the　approach　of　a　thunder…storm；　he　flew　it　well　up　into　the　threatening　clouds；　and　then；　touching；　the　suspended　key　with　his　knuckle；　received　the　electric　spark；　and　a　little　later　he　charged　a　Leyden　jar　from　the　electricity　drawn　from　the　clouds　with　his　kite。　In　a　brief　but　direct　letter；　he　sent　an　account　of　his　kite　and　his　experiment　to　England：　〃Make　a　small　cross　of　two　light　strips　of　cedar；〃　he　wrote；　〃the　arms　so　long　as　to　reach　to　the　four　corners　of　a　large；　thin；　silk　handkerchief　when　extended；　tie　the　corners　of　the　handkerchief　to　the　extremities　of　the　cross　so　you　have　the　body　of　a　kite；　which　being　properly　accommodated　with　a　tail；　loop；　and　string；　will　rise　in　the　air　like　those　made　of　paper；　but　this　being　of　silk　is　fitter　to　bear　the　wind　and　wet　of　a　thunder…gust　without　tearing。　To　the　top　of　the　upright　stick　of　the　cross　is　to　be　fixed　a　very　sharp…pointed　wire；　rising　a　foot　or　more　above　the　wood。　To　the　end　of　the　twine；　next　the　hand；　is　to　be　tied　a　silk　ribbon；　where　the　silk　and　twine　join　a　key　may　be　fastened。　This　kite　is　to　be　raised　when　a　thunder…gust　appears　to　be　coming　on；　and　the　person　who　holds　the　string　must　stand　within　a　door　or　window　or　under　some　cover；　so　that　the　silk　ribbon　may　not　be　wet；　and　care　must　be　taken　that　the　twine　does　not　touch　the　frame　of　the　door　or　window。　As　soon　as　any　of　the　thunder…clouds　come　over　the　kite；　the　pointed　wire　will　draw　the　electric　fire　from　them；　and　the　kite；　with　all　the　twine；　will　be　electrified　and　the　loose　filaments　will　stand　out　everywhere　and　be　attracted　by　the　approaching　finger；　and　when　the　rain　has　wet　the　kite　and　twine　so　that　it　can　conduct　the　electric　fire　freely；　you　will　find　it　stream　out　plentifully　from　the　key　on　the　approach　of　your　knuckle；　and　with　this　key　the　phial　may　be　charged；　and　from　electric　fire　thus　obtained　spirits　may　be　kindled　and　all　other　electric　experiments　performed　which　are　usually　done　by　the　help　of　a　rubbed　glass　globe　or　tube；　and　thereby　the　sameness　of　the　electric　matter　with　that　of　lightning　completely　demonstrated。〃＇5＇　In　experimenting　with　lightning　and　Franklin's　pointed　rods　in　Europe；　several　scientists　received　severe　shocks；　in　one　case　with　a　fatal　result。　Professor　Richman；　of　St。　Petersburg；　while　experimenting　during　a　thunder…storm；　with　an　iron　rod　which　he　had　erected　on　his　house；　received　a　shock　that　killed　him　instantly。　About　1733；　as　we　have　seen；　Dufay　had　demonstrated　that　there　were　two　apparently　different　kinds　of　electricity；　one　called　VITREOUS　because　produced　by　rubbing　glass；　and　the　other　RESINOUS　because　produced　by　rubbed　resinous　bodies。　Dufay　supposed　that　these　two　apparently　different　electricities　could　only　be　produced　by　their　respective　substances；　but　twenty　years　later；　John　Canton　（1715…1772）；　an　Englishman；　demonstrated　that　under　certain　conditions　both　might　be　produced　by　rubbing　the　same　substance。　Canton's　experiment；　made　upon　a　glass　tube　with　a　roughened　surface；　proved　that　if　the　surface　of　the　tube　were　rubbed　with　oiled　silk；　vitreous　or　positive　electricity　was　produced；　but　if　rubbed　with　flannel；　resinous　electricity　was　produced。　He　discovered　still　further　that　both　kinds　could　be　excited　on　the　same　tube　simultaneously　with　a　single　rubber。　To　demonstrate　this　he　used　a　tube；　one…half　of　which　had　a　roughened　the　other　a　glazed　surface。　With　a　single　stroke　of　the　rubber　he　was　able　to　excite　both　kinds　of　electricity　on　this　tube。　He　found　also　that　certain　substances；　such　as　glass　and　amber；　were　electrified　positively　when　taken　out　of　mercury；　and　this　led　to　his　important　discovery　that　an　amalgam　of　mercury　and　tin；　when　used　on　the　surface　of　the　rubber；　was　very　effective　in　exciting　glass。

XV。　NATURAL　HISTORY　TO　THE　TIME　OF　LINNAeUS　Modern　systematic　botany　and　zoology　are　usually　held　to　have　their　beginnings　with　Linnaeus。　But　there　were　certain　precursors　of　the　famous　Swedish　naturalist；　some　of　them　antedating　him　by　more　than　a　century；　whose　work　must　not　be　altogether　ignoredsuch　men　as　Konrad　Gesner　（1516…1565）；　Andreas　Caesalpinus　（1579…1603）；　Francisco　Redi　（1618…1676）；　Giovanni　Alfonso　Borelli　（1608…1679）；　John　Ray　（1628…1705）；　Robert　Hooke　（1635…1703）；　John　Swammerdam　（1637…1680）；　Marcello　Malpighi　（1628…1694）；　Nehemiah　Grew　（1628…1711）；　Joseph　Tournefort　（1656…1708）；　Rudolf　Jacob　Camerarius　（1665…1721）；　and　Stephen　Hales　（1677…1761）。　The　last　named　of　these　was；　to　be　sure；　a　contemporary　of　Linnaeus　himself；　but　Gesner　and　Caesalpinus　belong；　it　will　be　observed；　to　so　remote　an　epoch　as　that　of　Copernicus。　Reference　has　been　made　in　an　earlier　chapter　to　the　microscopic　investigations　of　Marcello　Malpighi；　who；　as　there　related；　was　the　first　observer　who　actually　saw　blood　corpuscles　pass　through　the　capillaries。　Another　feat　of　this　earliest　of　great　microscopists　was　to　dissect　muscular　tissue；　and　thus　become　the　father　of　microscopic　anatomy。　But　Malpighi　did　not　confine　his　observations　to　animal　tissues。　He　dissected　plants　as　well；　and　he　is　almost　as　fully　entitled　to　be　called　the　father　of　vegetable　anatomy；　though　here　his　honors　are　shared　by　the　Englishman　Grew。　In　1681；　while　Malpighi's　work；　Anatomia　plantarum；　was　on　its　way　to　the　Royal　Society　for　publication；　Grew's　Anatomy　of　Vegetables　was　in　the　hands　of　the　publishers；　making　its　appearance　a　few　months　earlier　than　the　work　of　the　great　Italian。　Grew's　book　was　epoch…marking　in　pointing　out　the　sex…differences　in　plants。　Robert　Hooke　developed　the　microscope；　and　took　the　first　steps　towards　studying　vegetable　anatomy；　publishing　in　1667；　among　other　results；　the　discovery　of　the　cellular　structure　of　cork。　Hooke　applied　the　name　〃cell〃　for　the　first　time　in　this　connection。　These　discoveries　of　Hooke；　Malpighi；　and　Grew；　and　the　discovery　of　the　circulation　of　the　blood　by　William　Harvey　shortly　before；　had　called　attention　to　the　similarity　of　animal　and　vegetable　structures。　Hales　made　a　series　of　investigations　upon　animals　to　determine　the　force　of　the　blood　pressure；　and　similarly　he　made　numerous　statical　experiments　to　determine　the　pressure　of　the　flow　of　sap　in　vegetables。　His　Vegetable　Statics；　published　in　1727；　was　the　first　important　work　on　the　subject　of　vegetable　physiology；　and　for　this　reason　Hales　has　been　called　the　father　of　this　branch　of　science。　In　botany；　as　well　as　in　zoology；　the　classifications　of　Linnaeus　of　course　supplanted　all　preceding　classifications；　for　the　obvious　reason　that　they　were　much　more　satisfactory；　but　his　work　was　a　culmination　of　many　similar　and　more　or　less　satisfactory　attempts　of　his　predecessors。　About　the　year　1670　Dr。　Robert　Morison　（1620…1683）；　of　Aberdeen；　published　a　classification　of　plants；　his　system　taking　into　account　the　woody　or　herbaceous　structure；　as　well　as　the　flowers　and　fruit。　This　classification　was　supplanted　twelve　years　later　by　the　classification　of　Ray；　who　arranged　all　known　vegetables　into　thirty…three　classes；　the　basis　of　this　classification　being　the　fruit。　A　few　years　later　Rivinus；　a　professor　of　botany　in　the　University　of　Leipzig；　made　still　another　classification；　determining　the　distinguishing　character　chiefly　from　the　flower；　and　Camerarius　and　Tournefort　also　made　elaborate　classifications。　On　the　Continent　Tournefort's　classification　was　the　most　popular　until　the　time　of　Linnaeus；　his　systematic　arrangement　including　about　eight　thousand　species　of　plants；　arranged　chiefly　according　to　the　form　of　the　corolla。　Most　of　these　early　workers　gave　attention　to　both　vegetable　and　animal　kingdoms。　They　were　called　naturalists；　and　the　field　of　their　investigations　was　spoken　of　as　〃natural　history。〃　The　specialization　of　knowledge　had　not　reached　that　later　stage　in　which　botanist；　zoologist；　and　physiologist　felt　their　labors　to　be　sharply　divided。　Such　a　division　was　becoming　more　and　more　necessary　as　the　field　of　knowledge　extended；　but　it　did　not　become　imperative　until　long　after　the　time　of　Linnaeus。　That　naturalist　himself；　as　we　shall　see；　was　equally　distinguished　as　botanist　and　as　zoologist。　His　great　task　of　organizing　knowledge　was　applied　to　the　entire　range　of　living　things。　Carolus　Linnaeus　was　born　in　the　town　of　Rashult；　in　Sweden；　on　May　13；　1707。　As　a　child　he　showed　great　aptitude　in　learning　botanical　names；　and　remembering　facts　about　various　plants　as　told　him　by　his　father。　His　eagerness　for　knowledge　did　not　extend　to　the　ordinary　primary　studies；　however；　and；　aside　from　the　single　exception　of　the　study　of　physiology；　he　proved　himself　an　indifferent　pupil。　His　backwardness　was　a　sore　trial　to　his　father；　who　was　desirous　that　his　son　should　enter　the　ministry；　but　as　the　young　Linnaeus　showed　no　liking　for　that　calling；　and　as　he　had　acquitted　himself　well　in　his　study　of　physiology；　his　father　at　last　decided　to　allow　him　to　take　up　the　study　of　medicine。　Here　at　last　was　a　field　more　to　the　liking　of　the　boy；　who　soon　vied　with　the　best　of　his　fellow…students　for　first　honors。　Meanwhile　he　kept　steadily　at　work　in　his　study　of　natural　history；　acquiring　considerabl