a history of science-1-第47节

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ded　Pytheas　as　regards　this　observation；　claiming　that　it　was　Hipparchus　and　not　Pytheas　who　made　the　second　observation　from　which　the　faulty　induction　was　drawn。　The　point　is　of　no　great　significance；　however；　except　as　showing　that　a　correct　method　of　determining　the　problems　of　latitude　had　thus　early　been　suggested。　That　faulty　observations　and　faulty　application　of　the　correct　principle　should　have　been　made　is　not　surprising。　Neither　need　we　concern　ourselves　with　the　details　as　to　the　geographical　distances；　which　Strabo　found　so　worthy　of　criticism　and　controversy。　But　in　leaving　the　great　geographer　we　may　emphasize　his　point　of　view　and　that　of　his　contemporaries　by　quoting　three　fundamental　principles　which　he　reiterates　as　being　among　the　〃facts　established　by　natural　philosophers。〃　He　tells　us　that　〃（1）　The　earth　and　heavens　are　spheroidal。　（2）　The　tendency　of　all　bodies　having　weight　is　towards　a　centre。　（3）　Further；　the　earth　being　spheroidal　and　having　the　same　centre　as　the　heavens；　is　motionless；　as　well　as　the　axis　that　passes　through　both　it　and　the　heavens。　The　heavens　turn　round　both　the　earth　and　its　axis；　from　east　to　west。　The　fixed　stars　turn　round　with　it　at　the　same　rate　as　the　whole。　These　fixed　stars　follow　in　their　course　parallel　circles；　the　principal　of　which　are　the　equator；　two　tropics；　and　the　arctic　circles；　while　the　planets；　the　sun；　and　the　moon　describe　certain　circles　comprehended　within　the　zodiac。〃＇4＇　Here；　then；　is　a　curious　mingling　of　truth　and　error。　The　Pythagorean　doctrine　that　the　earth　is　round　had　become　a　commonplace；　but　it　would　appear　that　the　theory　of　Aristarchus；　according　to　which　the　earth　is　in　motion；　has　been　almost　absolutely　forgotten。　Strabo　does　not　so　much　as　refer　to　it；　neither；　as　we　shall　see；　is　it　treated　with　greater　respect　by　the　other　writers　of　the　period。

TWO　FAMOUS　EXPOSITORSPLINY　AND　PTOLEMY　While　Strabo　was　pursuing　his　geographical　studies　at　Alexandria；　a　young　man　came　to　Rome　who　was　destined　to　make　his　name　more　widely　known　in　scientific　annals　than　that　of　any　other　Latin　writer　of　antiquity。　This　man　was　Plinius　Secundus；　who；　to　distinguish　him　from　his　nephew；　a　famous　writer　in　another　field；　is　usually　spoken　of　as　Pliny　the　Elder。　There　is　a　famous　story　to　the　effect　that　the　great　Roman　historian　Livy　on　one　occasion　addressed　a　casual　associate　in　the　amphitheatre　at　Rome；　and　on　learning　that　the　stranger　hailed　from　the　outlying　Spanish　province　of　the　empire；　remarked　to　him；　〃Yet　you　have　doubtless　heard　of　my　writings　even　there。〃　〃Then；〃　replied　the　stranger；　〃you　must　be　either　Livy　or　Pliny。〃　The　anecdote　illustrates　the　wide　fame　which　the　Roman　naturalist　achieved　in　his　own　day。　And　the　records　of　the　Middle　Ages　show　that　this　popularity　did　not　abate　in　succeeding　times。　Indeed；　the　Natural　History　of　Pliny　is　one　of　the　comparatively　few　bulky　writings　of　antiquity　that　the　efforts　of　copyists　have　preserved　to　us　almost　entire。　It　is；　indeed；　a　remarkable　work　and　eminently　typical　of　its　time；　but　its　author　was　an　industrious　compiler；　not　a　creative　genius。　As　a　monument　of　industry　it　has　seldom　been　equalled；　and　in　this　regard　it　seems　the　more　remarkable　inasmuch　as　Pliny　was　a　practical　man　of　affairs　who　occupied　most　of　his　life　as　a　soldier　fighting　the　battles　of　the　empire。　He　compiled　his　book　in　the　leisure　hours　stolen　from　sleep；　often　writing　by　the　light　of　the　camp…fire。　Yet　he　cites　or　quotes　from　about　four　thousand　works；　most　of　which　are　known　to　us　only　by　his　references。　Doubtless　Pliny　added　much　through　his　own　observations。　We　know　how　keen　was　his　desire　to　investigate；　since　he　lost　his　life　through　attempting　to　approach　the　crater　of　Vesuvius　on　the　occasion　of　that　memorable　eruption　which　buried　the　cities　of　Herculaneum　and　Pompeii。　Doubtless　the　wandering　life　of　the　soldier　had　given　Pliny　abundant　opportunity　for　personal　observation　in　his　favorite　fields　of　botany　and　zoology。　But　the　records　of　his　own　observations　are　so　intermingled　with　knowledge　drawn　from　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　abo