a history of science-4-第12节

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ver　the　style　of　architecture　it　helps　to　construct；　it　never　becomes　a　stone。　And　just　as　closely　does　each　atom　retain　its　own　peculiar　properties；　regardless　of　its　surroundings。

Thus；　for　example；　the　carbon　atom　may　take　part　in　the　formation　at　one　time　of　a　diamond；　again　of　a　piece　of　coal；　and　yet　again　of　a　particle　of　sugar；　of　wood　fibre；　of　animal　tissue；　or　of　a　gas　in　the　atmosphere；　but　from　first　to　lastfrom　glass…cutting　gem　to　intangible　gasthere　is　no　demonstrable　change　whatever　in　any　single　property　of　the　atom　itself。　So　far　as　we　know；　its　size；　its　weight；　its　capacity　for　vibration　or　rotation；　and　its　inherent　affinities；　remain　absolutely　unchanged　throughout　all　these　varying　fortunes　of　position　and　association。　And　the　same　thing　is　true　of　every　atom　of　all　of　the　seventy…odd　elementary　substances　with　which　the　modern　chemist　is　acquainted。　Every　one　appears　always　to　maintain　its　unique　integrity；　gaining　nothing　and　losing　nothing。

All　this　being　true；　it　would　seem　as　if　the　position　of　the　Daltonian　atom　as　a　primordial　bit　of　matter；　indestructible　and　non…transmutable；　had　been　put　to　the　test　by　the　chemistry　of　our　century；　and　not　found　wanting。　Since　those　early　days　of　the　century　when　the　electric　battery　performed　its　miracles　and　seemingly　reached　its　limitations　in　the　hands　of　Davy；　many　new　elementary　substances　have　been　discovered；　but　no　single　element　has　been　displaced　from　its　position　as　an　undecomposable　body。　Rather　have　the　analyses　of　the　chemist　seemed　to　make　it　more　and　more　certain　that　all　elementary　atoms　are　in　truth　what　John　Herschel　called　them；　〃manufactured　articles〃primordial；　changeless；　indestructible。

And　yet；　oddly　enough；　it　has　chanced　that　hand　in　hand　with　the　experiments　leading　to　such　a　goal　have　gone　other　experiments　arid　speculations　of　exactly　the　opposite　tenor。　In　each　generation　there　have　been　chemists　among　the　leaders　of　their　science　who　have　refused　to　admit　that　the　so…called　elements　are　really　elements　at　all　in　any　final　sense；　and　who　have　sought　eagerly　for　proof　which　might　warrant　their　scepticism。　The　first　bit　of　evidence　tending　to　support　this　view　was　furnished　by　an　English　physician；　Dr。　William　Prout；　who　in　1815　called　attention　to　a　curious　relation　to　be　observed　between　the　atomic　weight　of　the　various　elements。　Accepting　the　figures　given　by　the　authorities　of　the　time　（notably　Thomson　and　Berzelius）；　it　appeared　that　a　strikingly　large　proportion　of　the　atomic　weights　were　exact　multiples　of　the　weight　of　hydrogen；　and　that　others　differed　so　slightly　that　errors　of　observation　might　explain　the　discrepancy。　Prout　felt　that　it　could　not　be　accidental；　and　he　could　think　of　no　tenable　explanation；　unless　it　be　that　the　atoms　of　the　various　alleged　elements　are　made　up　of　different　fixed　numbers　of　hydrogen　atoms。　　Could　it　be　that　the　one　true　elementthe　one　primal　matteris　hydrogen；　and　that　all　other　forms　of　matter　are　but　compounds　of　this　original　substance？

Prout　advanced　this　startling　idea　at　first　tentatively；　in　an　anonymous　publication；　but　afterwards　he　espoused　it　openly　and　urged　its　tenability。　　Coming　just　after　Davy's　dissociation　of　some　supposed　elements；　the　idea　proved　alluring；　and　for　a　time　gained　such　popularity　that　chemists　were　disposed　to　round　out　the　observed　atomic　weights　of　all　elements　into　whole　numbers。　But　presently　renewed　determinations　of　the　atomic　weights　seemed　to　discountenance　this　practice；　and　Prout's　alleged　law　fell　into　disrepute。　　It　was　revived；　however；　about　1840；　by　Dumas；　whose　great　authority　secured　it　a　respectful　hearing；　and　whose　careful　redetermination　of　the　weight　of　carbon；　making　it　exactly　twelve　times　that　of　hydrogen；　aided　the　cause。

Subsequently　Stas；　the　pupil　of　Dumas；　undertook　a　long　series　of　determinations　of　atomic　weights；　with　the　expectation　of　confirming　the　Proutian　hypothesis。　　But　his　results　seemed　to　disprove　the　hypothesis；　for　the　atomic　weights　of　many　elements　differed　from　whole　numbers　by　more；　it　was　thought；　than　the　limits　of　error　of　the　experiments。　It　was　noteworthy；　however；　that　the　confidence　of　Dumas　was　not　shaken；　though　he　was　led　to　modify　the　hypothesis；　and；　in　accordance　with　previous　suggestions　of　Clark　and　of　Marignac；　to　recognize　as　the　primordial　element；　not　hydrogen　itself；　but　an　atom　half　the　weight；　or　even　one…fourth　the　weight；　of　that　of　hydrogen；　of　which　primordial　atom　the　hydrogen　atom　itself　is　compounded。　But　even　in　this　modified　form　the　hypothesis　found　great　opposition　from　experimental　observers。

In　1864；　however；　a　novel　relation　between　the　weights　of　the　elements　and　their　other　characteristics　was　called　to　the　attention　of　chemists　by　Professor　John　A。　R。　Newlands；　of　London；　who　had　noticed　that　if　the　elements　are　arranged　serially　in　the　numerical　order　of　their　atomic　weights；　there　is　a　curious　recurrence　of　similar　properties　at　intervals　of　eight　elements　This　so…called　〃law　of　octaves〃　attracted　little　immediate　attention；　but　the　facts　it　connotes　soon　came　under　the　observation　of　other　chemists；　notably　of　Professors　Gustav　Hinrichs　in　America；　Dmitri　Mendeleeff　in　Russia；　and　Lothar　Meyer　in　Germany。　　Mendeleeff　gave　the　discovery　fullest　expression；　explicating　it　in　1869；　under　the　title　of　〃the　periodic　law。〃

Though　this　early　exposition　of　what　has　since　been　admitted　to　be　a　most　important　discovery　was　very　fully　outlined；　the　generality　of　chemists　gave　it　little　heed　till　a　decade　or　so　later；　when　three　new　elements；　gallium；　scandium；　and　germanium；　were　discovered；　which；　on　being　analyzed；　were　quite　unexpectedly　found　to　fit　into　three　gaps　which　Mendeleeff　had　left　in　his　periodic　scale。　In　effect　the　periodic　law　had　enabled　Mendeleeff　to　predicate　the　existence　of　the　new　elements　years　before　they　were　discovered。　Surely　a　system　that　leads　to　such　results　is　no　mere　vagary。　So　very　soon　the　periodic　law　took　its　place　as　one　of　the　most　important　generalizations　of　chemical　science。

This　law　of　periodicity　was　put　forward　as　an　expression　of　observed　relations　independent　of　hypothesis；　but　of　course　the　theoretical　bearings　of　these　facts　could　not　be　overlooked。　As　Professor　J。　H。　Gladstone　has　said；　it　forces　upon　us　〃the　conviction　that　the　elements　are　not　separate　bodies　created　without　reference　to　one　another；　but　that　they　have　been　originally　fashioned；　or　have　been　built　up；　from　one　another；　according　to　some　general　plan。〃　　It　is　but　a　short　step　from　that　proposition　to　the　Proutian　hypothesis。


NEW　WEAPONSSPECTROSCOPE　AND　CAMERA

But　the　atomic　weights　are　not　alone　in　suggesting　the　compound　nature　of　the　alleged　elements。　　Evidence　of　a　totally　different　kind　has　contributed　to　the　same　end；　from　a　source　that　could　hardly　have　been　imagined　when　the　Proutian　hypothesis；　was　formulated；　through　the　tradition　of　a　novel　weapon　to　the　armamentarium　of　the　chemistthe　spectroscope。　　The　perfection　of　this　instrument；　in　the　hands　of　two　German　scientists；　Gustav　Robert　Kirchhoff　and　Robert　Wilhelm　Bunsen；　came　about　through　the　investigation；　towards　the　middle　of　the　century；　of　the　meaning　of　the　dark　lines　which　had　been　observed　in　the　solar　spectrum　by　Fraunhofer　as　early　as　1815；　and　by　Wollaston　a　decade　earlier。　It　was　suspected　by　Stokes　and　by　Fox　Talbot　in　England；　but　first　brought　to　demonstration　by　Kirchhoff　and　Bunsen；　that　these　lines；　which　were　known　to　occupy　definite　positions　in　the　spectrum；　are　really　indicative　of　particular　elementary　substances。　By　means　of　the　spectroscope；　which　is　essentially　a　magnifying　lens　attached　to　a　prism　of　glass；　it　is　possible　to　locate　the　lines　with　great　accuracy；　and　it　was　soon　shown　that　here　was　a　new　means　of　chemical　analysis　of　the　most　exquisite　delicacy。　It　was　found；　for　example；　that　the　spectroscope　could　detect　the　presence　of　a　quantity　of　sodium　so　infinitesimal　as　the　one　two…hundred…thousandth　of　a　grain。　　But　what　was　even　more　important；　the　spectroscope　put　no　limit　upon　the　distance　of　location　of　the　substance　it　tested；　provided　only　that　sufficient　light　came　from　it。　The　experiments　it　recorded　might　be　performed　in　the　sun；　or　in　the　most　distant　stars　or　nebulae；　indeed；　one　of　the　earliest　feats　of　the　instrument　was　to　wrench　from　the　sun　the　secret　of　his　chemical　constitution。

To　render　the　utility　of　the　spectroscope　complete；　however；　it　was　necessary　to　link　with　it　another　new　chemical　agencynamely；　photography。　　This　now　familiar　process　is　based　on　the　property　of　light　to　decompose　certain　unstable　compounds　of　silver；　and　thus　alter　their　chemical　composition。　Davy　and　Wedgwood　barely　escaped　the　discovery　of　the　value　of　the　photographic　method　early　in　the　nineteenth　century。　Their　successors　quite　overlooked　it　until　about　1826；　when　Louis　J。　M。　Daguerre；　the　French　chemist；　took　the　matter　in　hand；　and　after　many　years　of　experimentation　brought　it　to　relative　perfection　in　1839；　in　which　year　the　famous　daguerreotype　first　brought　the　matter　to　popular　attention。　In　the　same　year　Mr。　Fox　Talbot　read　a　paper　on　the　subject　before　the　Royal　Society；　and　soon　afterwards　the　efforts　of　Herschel　and　numerous　o