a history of science-1-第2章

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rimitive　man　must　have　conceived　that　the　earth　is　flat　and　of　limitless　extent。　By　this　it　is　not　meant　to　imply　that　he　had　a　distinct　conception　of　infinity；　but；　for　that　matter；　it　cannot　be　said　that　any　one　to…day　has　a　conception　of　infinity　that　could　be　called　definite。　But；　reasoning　from　experience　and　the　reports　of　travellers；　there　was　nothing　to　suggest　to　early　man　the　limit　of　the　earth。　He　did；　indeed；　find　in　his　wanderings；　that　changed　climatic　conditions　barred　him　from　farther　progress；　but　beyond　the　farthest　reaches　of　his　migrations；　the　seemingly　flat　land…surfaces　and　water…surfaces　stretched　away　unbroken　and；　to　all　appearances；　without　end。　It　would　require　a　reach　of　the　philosophical　imagination　to　conceive　a　limit　to　the　earth；　and　while　such　imaginings　may　have　been　current　in　the　prehistoric　period；　we　can　have　no　proof　of　them；　and　we　may　well　postpone　consideration　of　man's　early　dreamings　as　to　the　shape　of　the　earth　until　we　enter　the　historical　epoch　where　we　stand　on　firm　ground。　2。　Primitive　man　must；　from　a　very　early　period；　have　observed　that　the　sun　gives　heat　and　light；　and　that　the　moon　and　stars　seem　to　give　light　only　and　no　heat。　It　required　but　a　slight　extension　of　this　observation　to　note　that　the　changing　phases　of　the　seasons　were　associated　with　the　seeming　approach　and　recession　of　the　sun。　This　observation；　however；　could　not　have　been　made　until　man　had　migrated　from　the　tropical　regions；　and　had　reached　a　stage　of　mechanical　development　enabling　him　to　live　in　subtropical　or　temperate　zones。　Even　then　it　is　conceivable　that　a　long　period　must　have　elapsed　before　a　direct　causal　relation　was　felt　to　exist　between　the　shifting　of　the　sun　and　the　shifting　of　the　seasons；　because；　as　every　one　knows；　the　periods　of　greatest　heat　in　summer　and　greatest　cold　in　winter　usually　come　some　weeks　after　the　time　of　the　solstices。　Yet；　the　fact　that　these　extremes　of　temperature　are　associated　in　some　way　with　the　change　of　the　sun's　place　in　the　heavens　must；　in　time；　have　impressed　itself　upon　even　a　rudimentary　intelligence。　It　is　hardly　necessary　to　add　that　this　is　not　meant　to　imply　any　definite　knowledge　of　the　real　meaning　of；　the　seeming　oscillations　of　the　sun。　We　shall　see　that；　even　at　a　relatively　late　period；　the　vaguest　notions　were　still　in　vogue　as　to　the　cause　of　the　sun's　changes　of　position。　That　the　sun；　moon；　and　stars　move　across　the　heavens　must　obviously　have　been　among　the　earliest　scientific　observations。　It　must　not　be　inferred；　however；　that　this　observation　implied　a　necessary　conception　of　the　complete　revolution　of　these　bodies　about　the　earth。　It　is　unnecessary　to　speculate　here　as　to　how　the　primitive　intelligence　conceived　the　transfer　of　the　sun　from　the　western　to　the　eastern　horizon；　to　be　effected　each　night；　for　we　shall　have　occasion　to　examine　some　historical　speculations　regarding　this　phenomenon。　We　may　assume；　however；　that　the　idea　of　the　transfer　of　the　heavenly　bodies　beneath　the　earth　（whatever　the　conception　as　to　the　form　of　that　body）　must　early　have　presented　itself。　It　required　a　relatively　high　development　of　the　observing　faculties；　yet　a　development　which　man　must　have　attained　ages　before　the　historical　period；　to　note　that　the　moon　has　a　secondary　motion；　which　leads　it　to　shift　its　relative　position　in　the　heavens；　as　regards　the　stars；　that　the　stars　themselves；　on　the　other　hand；　keep　a　fixed　relation　as　regards　one　another；　with　the　notable　exception　of　two　or　three　of　the　most　brilliant　members　of　the　galaxy；　the　latter　being　the　bodies　which　came　to　be　known　finally　as　planets；　or　wandering　stars。　The　wandering　propensities　of　such　brilliant　bodies　as　Jupiter　and　Venus　cannot　well　have　escaped　detection。　We　may　safely　assume；　however；　that　these　anomalous　motions　of　the　moon　and　planets　found　no　explanation　that　could　be　called　scientific　until　a　relatively　late　period。　3。　Turning　from　the　heavens　to　the　earth；　and　ignoring　such　primitive　observations　as　that　of　the　distinction　between　land　and　water；　we　may　note　that　there　was　one　great　scientific　law　which　must　have　forced　itself　upon　the　attention　of　primitive　man。　This　is　the　law　of　universal　terrestrial　gravitation。　The　word　gravitation　suggests　the　name　of　Newton；　and　it　may　excite　surprise　to　hear　a　knowledge　of　gravitation　ascribed　to　men　who　preceded　that　philosopher　by；　say；　twenty…five　or　fifty　thousand　years。　Yet　the　slightest　consideration　of　the　facts　will　make　it　clear　that　the　great　central　law　that　all　heavy　bodies　fall　directly　towards　the　earth；　cannot　have　escaped　the　attention　of　the　most　primitive　intelligence。　The　arboreal　habits　of　our　primitive　ancestors　gave　opportunities　for　constant　observation　of　the　practicalities　of　this　law。　And；　so　soon　as　man　had　developed　the　mental　capacity　to　formulate　ideas；　one　of　the　earliest　ideas　must　have　been　the　conception；　however　vaguely　phrased　in　words；　that　all　unsupported　bodies　fall　towards　the　earth。　The　same　phenomenon　being　observed　to　operate　on　water…surfaces；　and　no　alteration　being　observed　in　its　operation　in　different　portions　of　man's　habitat；　the　most　primitive　wanderer　must　have　come　to　have　full　faith　in　the　universal　action　of　the　observed　law　of　gravitation。　Indeed；　it　is　inconceivable　that　he　can　have　imagined　a　place　on　the　earth　where　this　law　does　not　operate。　On　the　other　hand；　of　course；　he　never　grasped　the　conception　of　the　operation　of　this　law　beyond　the　close　proximity　of　the　earth。　To　extend　the　reach　of　gravitation　out　to　the　moon　and　to　the　stars；　including　within　its　compass　every　particle　of　matter　in　the　universe；　was　the　work　of　Newton；　as　we　shall　see　in　due　course。　Meantime　we　shall　better　understand　that　work　if　we　recall　that　the　mere　local　fact　of　terrestrial　gravitation　has　been　the　familiar　knowledge　of　all　generations　of　men。　It　may　further　help　to　connect　us　in　sympathy　with　our　primeval　ancestor　if　we　recall　that　in　the　attempt　to　explain　this　fact　of　terrestrial　gravitation　Newton　made　no　advance；　and　we　of　to…day　are　scarcely　more　enlightened　than　the　man　of　the　Stone　Age。　Like　the　man　of　the　Stone　Age；　we　know　that　an　arrow　shot　into　the　sky　falls　back　to　the　earth。　We　can　calculate；　as　he　could　not　do；　the　arc　it　will　describe　and　the　exact　speed　of　its　fall；　but　as　to　why　it　returns　to　earth　at　all；　the　greatest　philosopher　of　to…day　is　almost　as　much　in　the　dark　as　was　the　first　primitive　bowman　that　ever　made　the　experiment。　Other　physical　facts　going　to　make　up　an　elementary　science　of　mechanics；　that　were　demonstratively　known　to　prehistoric　man；　were　such　as　these：　the　rigidity　of　solids　and　the　mobility　of　liquids；　the　fact　that　changes　of　temperature　transform　solids　to　liquids　and　vice　versathat　heat；　for　example；　melts　copper　and　even　iron；　and　that　cold　congeals　water；　and　the　fact　that　friction；　as　illustrated　in　the　rubbing　together　of　two　sticks；　may　produce　heat　enough　to　cause　a　fire。　The　rationale　of　this　last　experiment　did　not　receive　an　explanation　until　about　the　beginning　of　the　nineteenth　century　of　our　own　era。　But　the　experimental　fact　was　so　well　known　to　prehistoric　man　that　he　employed　this　method；　as　various　savage　tribes　employ　it　to　this　day；　for　the　altogether　practical　purpose　of　making　a　fire；　just　as　he　employed　his　practical　knowledge　of　the　mutability　of　solids　and　liquids　in　smelting　ores；　in　alloying　copper　with　tin　to　make　bronze；　and　in　casting　this　alloy　in　molds　to　make　various　implements　and　weapons。　Here；　then；　were　the　germs　of　an　elementary　science　of　physics。　Meanwhile　such　observations　as　that　of　the　solution　of　salt　in　water　may　be　considered　as　giving　a　first　lesson　in　chemistry；　but　beyond　such　altogether　rudimentary　conceptions　chemical　knowledge　could　not　have　goneunless；　indeed；　the　practical　observation　of　the　effects　of　fire　be　included；　nor　can　this　well　be　overlooked；　since　scarcely　another　single　line　of　practical　observation　had　a　more　direct　influence　in　promoting　the　progress　of　man　towards　the　heights　of　civilization。　4。　In　the　field　of　what　we　now　speak　of　as　biological　knowledge；　primitive　man　had　obviously　the　widest　opportunity　for　practical　observation。　We　can　hardly　doubt　that　man　attained；　at　an　early　day；　to　that　conception　of　identity　and　of　difference　which　Plato　places　at　the　head　of　his　metaphysical　system。　We　shall　urge　presently　that　it　is　precisely　such　general　ideas　as　these　that　were　man's　earliest　inductions　from　observation；　and　hence　that　came　to　seem　the　most　universal　and　〃innate〃　ideas　of　his　mentality。　It　is　quite　inconceivable；　for　example；　that　even　the　most　rudimentary　intelligence　that　could　be　called　human　could　fail　to　discriminate　between　living　things　and；　let　us　say；　the　rocks　of　the　earth。　The　most　primitive　intelligence；　then；　must　have　made　a　tacit　classification　of　the　natural　objects　about　it　into　the　grand　divisions　of　animate　and　inanimate　nature。　Doubtless　the　nascent　scientist　may　have　imagined　life　animating　many　bodies　that　we　should　call　inanimatesuch　as　the　sun；　wandering　planets；　the　winds；　and　lightning；　and；　on　the　other　hand；　he　may　quite　likely　have　relegated　such　objects　as　trees　to　the　ranks　of　the　non…living；　but　that　he　recognized　a　fundamental