a history of science-1-第3章

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ved　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　distinction　between；　let　us　say；　a　wolf　and　a　granite　bowlder　we　cannot　well　doubt。　A　step　beyond　thisa　step；　however；　that　may　have　required　centuries　or　millenniums　in　the　takingmust　have　carried　man　to　a　plane　of　intelligence　from　which　a　primitive　Aristotle　or　Linnaeus　was　enabled　to　note　differences　and　resemblances　connoting　such　groups　of　things　as　fishes；　birds；　and　furry　beasts。　This　conception；　to　be　sure；　is　an　abstraction　of　a　relatively　high　order。　We　know　that　there　are　savage　races　to…day　whose　language　contains　no　word　for　such　an　abstraction　as　bird　or　tree。　We　are　bound　to　believe；　then；　that　there　were　long　ages　of　human　progress　during　which　the　highest　man　had　attained　no　such　stage　of　abstraction；　but；　on　the　other　hand；　it　is　equally　little　in　question　that　this　degree　of　mental　development　had　been　attained　long　before　the　opening　of　our　historical　period。　The　primeval　man；　then；　whose　scientific　knowledge　we　are　attempting　to　predicate；　had　become；　through　his　conception　of　fishes；　birds；　and　hairy　animals　as　separate　classes；　a　scientific　zoologist　of　relatively　high　attainments。　In　the　practical　field　of　medical　knowledge；　a　certain　stage　of　development　must　have　been　reached　at　a　very　early　day。　Even　animals　pick　and　choose　among　the　vegetables　about　them；　and　at　times　seek　out　certain　herbs　quite　different　from　their　ordinary　food；　practising　a　sort　of　instinctive　therapeutics。　The　cat's　fondness　for　catnip　is　a　case　in　point。　The　most　primitive　man；　then；　must　have　inherited　a　racial　or　instinctive　knowledge　of　the　medicinal　effects　of　certain　herbs；　in　particular　he　must　have　had　such　elementary　knowledge　of　toxicology　as　would　enable　him　to　avoid　eating　certain　poisonous　berries。　Perhaps；　indeed；　we　are　placing　the　effect　before　the　cause　to　some　extent；　for；　after　all；　the　animal　system　possesses　marvellous　powers　of　adaption；　and　there　is　perhaps　hardly　any　poisonous　vegetable　which　man　might　not　have　learned　to　eat　without　deleterious　effect；　provided　the　experiment　were　made　gradually。　To　a　certain　extent；　then；　the　observed　poisonous　effects　of　numerous　plants　upon　the　human　system　are　to　be　explained　by　the　fact　that　our　ancestors　have　avoided　this　particular　vegetable。　Certain　fruits　and　berries　might　have　come　to　have　been　a　part　of　man's　diet；　had　they　grown　in　the　regions　he　inhabited　at　an　early　day；　which　now　are　poisonous　to　his　system。　This　thought；　however；　carries　us　too　far　afield。　For　practical　purposes；　it　suffices　that　certain　roots；　leaves；　and　fruits　possess　principles　that　are　poisonous　to　the　human　system；　and　that　unless　man　had　learned　in　some　way　to　avoid　these；　our　race　must　have　come　to　disaster。　In　point　of　fact；　he　did　learn　to　avoid　them；　and　such　evidence　implied；　as　has　been　said；　an　elementary　knowledge　of　toxicology。　Coupled　with　this　knowledge　of　things　dangerous　to　the　human　system；　there　must　have　grown　up；　at　a　very　early　day；　a　belief　in　the　remedial　character　of　various　vegetables　as　agents　to　combat　disease。　Here；　of　course；　was　a　rudimentary