a history of science-1-第39章

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！


m　books　that　it　is　difficult　to　distinguish　the　one　from　the　other。　Nor　does　this　greatly　matter；　for　whether　as　closet…student　or　field…naturalist；　Pliny's　trait　of　mind　is　essentially　that　of　the　compiler。　He　was　no　philosophical　thinker；　no　generalizer；　no　path…maker　in　science。　He　lived　at　the　close　of　a　great　progressive　epoch　of　thought；　in　one　of　those　static　periods　when　numberless　observers　piled　up　an　immense　mass　of　details　which　might　advantageously　be　sorted　into　a　kind　of　encyclopaedia。　Such　an　encyclopaedia　is　the　so…called　Natural　History　of　Pliny。　It　is　a　vast　jumble　of　more　or　less　uncritical　statements　regarding　almost　every　field　of　contemporary　knowledge。　The　descriptions　of　animals　and　plants　predominate；　but　the　work　as　a　whole　would　have　been　immensely　improved　had　the　compiler　shown　a　more　critical　spirit。　As　it　is；　he　seems　rather　disposed　to　quote　any　interesting　citation　that　he　comes　across　in　his　omnivorous　readings；　shielding　himself　behind　an　equivocal　〃it　is　said；〃　or　〃so　and　so　alleges。〃　A　single　illustration　will　suffice　to　show　what　manner　of　thing　is　thought　worthy　of　repetition。　〃It　is　asserted；〃　he　says；　〃that　if　the　fish　called　a　sea…star　is　smeared　with　the　fox's　blood　and　then　nailed　to　the　upper　lintel　of　the　door；　or　to　the　door　itself；　with　a　copper　nail；　no　noxious　spell　will　be　able　to　obtain　admittance；　or；　at　all　events；　be　productive　of　any　ill　effects。〃　It　is　easily　comprehensible　that　a　work　fortified　with　such　practical　details　as　this　should　have　gained　wide　popularity。　Doubtless　the　natural　histories　of　our　own　day　would　find　readier　sale　were　they　to　pander　to　various　superstitions　not　altogether　different　from　that　here　suggested。　The　man；　for　example；　who　believes　that　to　have　a　black　cat　cross　his　path　is　a　lucky　omen　would　naturally　find　himself　attracted　by　a　book　which　took　account　of　this　and　similar　important　details　of　natural　history。　Perhaps；　therefore；　it　was　its　inclusion　of　absurdities；　quite　as　much　as　its　legitimate　value；　that　gave　vogue　to　the　celebrated　work　of　Pliny。　But　be　that　as　it　may；　the　most　famous　scientist　of　Rome　must　be　remembered　as　a　popular　writer　rather　than　as　an　experimental　worker。　In　the　history　of　the　promulgation　of　scientific　knowledge　his　work　is　important；　in　the　history　of　scientific　principles　it　may　virtually　be　disregarded。

PTOLEMY；　THE　LAST　GREAT　ASTRONOMER　OF　ANTIQUITY　Almost　the　same　thing　may　be　said　of　Ptolemy；　an　even　more　celebrated　writer；　who　was　born　not　very　long　after　the　death　of　Pliny。　The　exact　dates　of　Ptolemy's　life　are　not　known；　but　his　recorded　observations　extend　to　the　year　151　A。D。　He　was　a　working　astronomer；　and　he　made　at　least　one　original　discovery　of　some　significancenamely；　the　observation　of　a　hitherto　unrecorded　irregularity　of　the　moon's　motion；　which　came　to　be　spoken　of　as　the　moon's　evection。　This　consists　of　periodical　aberrations　from　the　moon's　regular　motion　in　its　orbit；　which；　as　we　now　know；　are　due　to　the　gravitation　pull　of　the　sun；　but　which　remained　unexplained　until　the　time　of　Newton。　Ptolemy　also　made　original　observations　as　to　the　motions　of　the　planets。　He　is；　therefore；　entitled　to　a　respectable　place　as　an　observing　astronomer；　but　his　chief　fame　rests　on　his　writings。　His　great　works　have　to　do　with　geography　and　astronomy。　In　the　former　field　he　makes　an　advance　upon　Strabo；　citing　the　latitude　of　no　fewer　than　five　thousand　places。　In　the　field　of　astronomy；　his　great　service　was　to　have　made　known　to　the　world　the　labors　of　Hipparchus。　Ptolemy　has　been　accused　of　taking　the　star…chart　of　his　great　predecessor　without　due　credit；　and　indeed　it　seems　difficult　to　clear　him　of　this　charge。　Yet　it　is　at　least　open　to　doubt　whether　be　intended　any　impropriety；　inasmuch　as　be　all　along　is　sedulous　in　his　references　to　his　predecessor。　Indeed；　his　work　might　almost　be　called　an　exposition　of　the　astronomical　doctrines　of　Hipparchus。　No　one　pretends　that　Ptolemy　is　to　be　compared　with　the　Rhodesian　observer　as　an　original　investigator；　but　as　a　popular　expounder　his　superiority　is　evidenced　in　the　fact　that　the　writings　of　Ptolemy　became　practically　the　sole　astronomical　text…book　of　the　Middle　Ages　both　in　the　East　and　in　the　West；　while　the　writings　of　Hipparchus　were　allowed　to　perish。　The　most　noted　of　all　the　writings　of　Ptolemy　is　the　work　which　became　famous　under　the　Arabic　name　of　Almagest。　This　word　is　curiously　derived　from　the　Greek　title　；　〃the　greatest　construction；〃　a　name　given　the　book　to　distinguish　it　from　a　work　on　astrology　in　four　books　by　the　same　author。　For　convenience　of　reference　it　came　to　be　spoken　of　merely　as　；　from　which　the　Arabs　form　the　title　Tabair　al　Magisthi；　under　which　title　the　book　was　published　in　the　year　827。　From　this　it　derived　the　word　Almagest；　by　which　Ptolemy's　work　continued　to　be　known　among　the　Arabs；　and　subsequently　among　Europeans　when　the　book　again　became　known　in　the　West。　Ptolemy's　book；　as　has　been　said；　is　virtually　an　elaboration　of　the　doctrines　of　Hipparchus。　It　assumes　that　the　earth　is　the　fixed　centre　of　the　solar　system；　and　that　the　stars　and　planets　revolve　about　it　in　twenty…four　hours；　the　earth　being；　of　course；　spherical。　It　was　not　to　be　expected　that　Ptolemy　should　have　adopted　the　heliocentric　idea　of　Aristarchus。　Yet　it　is　much　to　be　regretted　that　he　failed　to　do　so；　since　the　deference　which　was　accorded　his　authority　throughout　the　Middle　Ages　would　doubtless　have　been　extended　in　some　measure　at　least　to　this　theory　as　well；　had　he　championed　it。　Contrariwise；　his　unqualified　acceptance　of　the　geocentric　doctrine　sufficed　to　place　that　doctrine　beyond　the　range　of　challenge。　The　Almagest　treats　of　all　manner　of　astronomical　problems；　but　the　feature　of　it　which　gained　it　widest　celebrity　was　perhaps　that　which　has　to　do　with　eccentrics　and　epicycles。　This　theory　was；　of　course；　but　an　elaboration　of　the　ideas　of　Hipparchus；　but；　owing　to　the　celebrity　of　the　expositor；　it　has　come　to　be　spoken　of　as　the　theory　of　Ptolemy。　We　have　sufficiently　detailed　the　theory　in　speaking　of　Hipparchus。　It　should　be　explained；　however；　that；　with　both　Hipparchus　and　Ptolemy；　the　theory　of　epicycles　would　appear　to　have　been　held　rather　as　a　working　hypothesis　than　as　a　certainty；　so　far　as　the　actuality　of　the　minor　spheres　or　epicycles　is　concerned。　That　is　to　say；　these　astronomers　probably　did　not　conceive　either　the　epicycles　or　the　greater　spheres　as　constituting　actual　solid　substances。　Subsequent　generations；　however；　put　this　interpretation　upon　the　theory；　conceiving　the　various　spheres　as　actual　crystalline　bodies。　It　is　difficult　to　imagine　just　how　the　various　epicycles　were　supposed　to　revolve　without　interfering　with　the　major　spheres；　but　perhaps　this　is　no　greater　difficulty　than　is　presented　by　the　alleged　properties　of　the　ether；　which　physicists　of　to…day　accept　as　at　least　a　working　hypothesis。　We　shall　see　later　on　how　firmly　the　conception　of　concentric　crystalline　spheres　was　held　to；　and　that　no　real　challenge　was　ever　given　that　theory　until　the　discovery　was　made　that　comets　have　an　orbit　that　must　necessarily　intersect　the　spheres　of　the　various　planets。　Ptolemy's　system　of　geography　in　eight　books；　founded　on　that　of　Marinus　of　Tyre；　was　scarcely　less　celebrated　throughout　the　Middle　Ages　than　the　Almagest。　It　contained　little；　however；　that　need　concern　us　here；　being　rather　an　elaboration　of　the　doctrines　to　which　we　have　already　sufficiently　referred。　None　of　Ptolemy's　original　manuscripts　has　come　down　to　us；　but　there　is　an　alleged　fifth…century　manuscript　attributed　to　Agathadamon　of　Alexandria　which　has　peculiar　interest　because　it　contains　a　series　of　twenty…seven　elaborately　colored　maps　that　are　supposed　to　be　derived　from　maps　drawn　up　by　Ptolemy　himself。　In　these　maps　the　sea　is　colored　green；　the　mountains　red　or　dark　yellow；　and　the　land　white。　Ptolemy　assumed　that　a　degree　at　the　equator　was　500　stadia　instead　of　604　stadia　in　length。　We　are　not　informed　as　to　the　grounds　on　which　this　assumption　was　made；　but　it　has　been　suggested　that　the　error　was　at　least　partially　instrumental　in　leading　to　one　very　curious　result。　〃Taking　the　parallel　of　Rhodes；〃　says　Donaldson；＇5＇　〃he　calculated　the　longitudes　from　the　Fortunate　Islands　to　Cattigara　or　the　west　coast　of　Borneo　at　180　degrees；　conceiving　this　to　be　one…half　the　circumference　of　the　globe。　The　real　distance　is　only　125　degrees　or　127　degrees；　so　that　his　measurement　is　wrong　by　one　third　of　the　whole；　one…sixth　for　the　error　in　the　measurement　of　a　degree　and　one…sixth　for　the　errors　in　measuring　the　distance　geometrically。　These　errors；　owing　to　the　authority　attributed　to　the　geography　of　Ptolemy　in　the　Middle　Ages；　produced　a　consequence　of　the　greatest　importance。　They　really　led　to　the　discovery　of　America。　For　the　design　of　Columbus　to　sail　from　the　west　of　Europe　to　the　east　of　Asia　was　founded　on　the　supposition　that　the　distance　was　less　by　one　third　than　it　really　was。〃　This　view　is　perhaps　a　trifle　fanciful；　since　there　is　nothing　to　suggest　that　the　courage　of　Columbus　would　have　balked　at　the　greater　distance；　and　since　the　protests　of　the　sailors；　which　nearly　thwarted　his　efforts；　were　made　long　before　the　distance　as　estimated　by　Ptolemy　had　been　covered；　nevertheless　it　is　interesting　to　recall　that　the　great　geographical　doctrines；　upon　which　Columbus　must　chiefly　have　based　his　arguments；　had　been　before　the　world　in　an　authoritative　form　practically　unheeded　for　more　than　twelve　hundred　years；　awaiting　a　champion　with　courage　enough　to　put　them　to　the　test。

GALENTHE　LAST　GREAT　ALEXANDRIAN　There　is　one　other　field　of　scientific　investigation　to　which　we　must　give　brief　attention　before　leaving　the　antique　world。　This　is　the　field　of　physiology　and　medicine。　In　considering　it　we　shall　have　to　do　with　the　very　last　great　scientist　of　the　Alexandrian　school。　This　was　Claudius　Galenus；　commonly　known　as　Galen；　a　man　whose　fame　was　destined　to　eclipse　that　of　all　other　physicians　of　antiquity　except　Hippocrates；　and　whose　doctrines　were　to　have　the　same　force　in　their　field　throughout　the　Middle　Ages　that　the　doctrines　of　Aristotle　had　for　physical　science。　But　before　we　take　up　Galen's　specific　labors；　it　will　be　well　to　inquire　briefly　as　to　the　state　of　medical　art　and　science　in　the　Roman　world　at　the　time　when　the　last　great　physician　of　antiquity　came　upon　the　scene。　The　Romans；　it　would　appear；　had　done　little　in　the　way　of　scientific　discoveries　in　the　field　of　medicine；　but；　nevertheless；　with　their　practicality　of　mind；　they　had　turned　to　better　account　many　more　of　the　scientific　discoveries　of　the　Greeks　than　did　the　discoverers　themselves。　The　practising　physicians　in　early　Rome　were　mostly　men　of　Greek　origin；　who　came　to　the　capital　after　the　overthrow　of　the　Greeks　by　the　Romans。　Many　of　them　were　slaves；　as　earning　money　by　either　bodily　or　mental　labor　was　considered　beneath　the　dignity　of　a　Roman　citizen。　The　wealthy　Romans；　who　owned　large　estates　and　numerous　slaves；　were　in　the　habit　of　purchasing　some　of　these　slave　doctors；　and　thus　saving　medical　fees　by　having　them　attend　to　the　health　of　their　families。　By　the　beginning　of　the　Christian　era　medici