decline of science in england-第13节

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The　remarkable　agreement　with　each　other；　which　was　found　to　exist　amongst　each　class　of　observations；　was　as　unexpected　by　those　most　conversant　with　the　respective　processes；　as　it　was　creditable　to　one　who　had　devoted　but　a　few　years　to　the　subject；　and　who；　in　the　course　of　those　voyages；　used　some　of　the　instruments　for　the　first　time　in　his　life。

This　accordance　amongst　the　results　was　such；　that　naval　officers　of　the　greatest　experience；　confessed　themselves　unable　to　take　such　lunars；　whilst　other　observers；　long　versed　in　the　use　of　the　transit　instrument；　avowed　their　inability　to　take　such　transits。　　Those　who　were　conversant　with　pendulums；　were　at　a　loss　how　to　make；　even　under　more　favourable　circumstances；　similarly　concordant　observations。　　The　same　opinion　prevailed　on　the　continent　as　well　as　in　England。　On　whatever　subject　Captain　Sabine　touched；　the　observations　he　published　seemed　by　their　accuracy　to　leave　former　observers　at　a　distance。　The　methods　of　using　the　instruments　scarcely　differed　in　any　important　point　from　those　before　adopted；　and；　but　for　a　fortunate　discovery；　which　I　shall　presently　relate；　the　world　must　have　concluded　that　Captain　Sabine　possessed　some　keenness　of　vision；　or　acuteness　of　touch；　which　it　would　be　hopeless　for　any　to　expect　to　rival。

The　Council　of　the　Royal　Society　spared　no　pains　to　stamp　the　accuracy　of　these　observations　with　their　testimony。　　They　seem　to　have　thrust　Captain　Sabine's　name　perpetually　on　their　minutes；　and　in　a　manner　which　must　have　been　almost　distressing：　they　recommend　him　in　a　letter　to　the　Admiralty；　then　in　another　to　the　Ordnance；　and　several　of　the　same　persons；　in　their　other　capacity；　as　members　of　the　Board　of　Longitude；　after　voting　him　a　THOUSAND　POUNDS　for　these　observations；　are　said　to　have　again　recommended　him　to　the　Master…General　of　the　Ordnance。　　That　an　officer；　commencing　his　scientific　career；　should　be　misled　by　such　praises；　was　both　natural　and　pardonable；　but　that　the　Council　of　the　Royal　Society　should　adopt　their　opinion　so　heedlessly；　and　maintain　it　so　pertinaciously；　was　as　cruel　to　the　observer　as　it　was　injurious　to　the　interests　of　science。

It　might　have　been　imagined　that　such　praises；　together　with　the　Copley　medal；　presented　to　Captain　Sabine　by　the　Royal　Society；　and　the　medal　of　Lalande；　given　to　him　by　the　Institute　of　France；　had　arisen　from　such　a　complete　investigation　of　his　observations；　as　should　place　them　beyond　the　reach　even　of　criticism。　　But；　alas！　the　Royal　Society　may　write；　and　nobody　will　attend；　its　medals　have　lost　their　lustre；　and　even　the　Institute　of　France　may　find　that　theirs　cannot　confer　immortality。　　That　learned　body　is　in　the　habit　of　making　most　interesting　and　profound　reports　on　any　memoirs　communicated　to　it；　nothing　escapes　the　penetration　of　their　committees　appointed　for　such　purposes。　Surely；　when　they　enter　on　the　much　more　important　subject　of　the　award　of　a　medal；　unusual　pains　must　be　taken　with　the　previous　report；　and　it　might；　perhaps；　be　of　some　advantage　to　science；　and　might　furnish　their　admirers　with　arguments　in　their　defence；　if　they　would　publish　that　on　which　the　decree　of　their　Lalande's　medal　to　Captain　Sabine　was　founded。

It　is　far　from　necessary　to　my　present　object；　to　state　all　that　has　been　written　and　said　respecting　these　pendulum　experiments：　I　shall　confine　myself　merely　to　two　points；　one；　the　transit　observations；　I　shall　allude　to；　because　I　may　perhaps　show　the　kind　of　feeling　that　exists　respecting　them；　and　possibly　enable　Captain　Sabine　to　explain　them。　　The　other　point；　the　error　in　the　estimation　of　the　division　of　the　level；　I　shall　discuss；　because　it　is　an　admitted　fact。

Some　opinion　may　be　formed　of　transit　observations；　by　taking　the　difference　of　times　of　the　passage　of　any　star　between　the　several　wires；　supposing　the　distances　of　those　wires　equal；　the　intervals　of　time　occupied　by　the　star　in　passing　from　one　to　the　other；　ought　to　be　precisely　the　same。　　As　those　times　of　passing　from　one　wire　to　another　are　usually　given　to　seconds　and　tenths　of　seconds；　it　rarely　happens　that　the　accordance　is　perfect。

The　transit　instrument　used　by　Captain　Sabine　was　thirty　inches　in　length；　and　the　wires　are　stated　to　be　equi…distant。　　Out　of　about　370　transits；　there　are　eighty…seven；　or　nearly　one…fourth；　which　have　the　intervals　between　all　the　wires　agreeing　to　the　same；　the　tenth　of　a　second。　At　Sierra　Leone；　nineteen　out　of　seventy…two　have　the　same　accordance；　and　of　the　moon　culminating　stars；　p。　409；　twelve　out　of　twenty…four　are　equally　exact。　　With　larger　instruments；　and　in　great　observatories；　this　is　not　always　the　case。

Captain　Kater　has　given；　in　the　Philosophical　Transactions；　1819；　p。　427；　a　series　of　transits；　with　a　three　and　a　half　foot　transit；　in　which　about　one…eleventh　part　of　them　only　have　this　degree　of　accuracy；　and　it　should　be　observed　that　not　merely　the　instrument；　but　the　stars　selected；　have；　in　this　instance；　an　advantage　over　Captain　Sabine's。

The　transit　of　M。　Bessel　is　five　feet　in　length；　made　by　Frauenhofer；　and　the　magnifying　power　employed　is　182；　yet；　out　of　some　observations　of　his　in　January；　1826；　only　one…eleventh　have　this　degree　of　accordance。　　In　thirty…three　of　the　Greenwich　observations　of　January；　1828；　fifteen　have　this　agreement；　or　five…elevenths；　but　this　is　with　a　ten…feet　transit。　　Now　in　none　of　these　instances　do　the　times　agree　within　a　tenth　of　a　second　between　all　the　wires；　but　I　have　accounted　those　as　agreeing　in　all　the　wires　in　which　there　is　not　more　than　four…tenths　of　a　second　between　the　greatest　and　least。

This　superior　accuracy　of　the　small　instrument　requires　some　explanation。　　One　which　has　been　suggested　is；　that　Captain　Sabine　employs　a　chronometer　to　observe　transits　with；　and　that　since　it　beats　five　times　in　two　seconds；　each　beat　will　give　four…tenths　of　a　second；　and　this　being　the　smallest　quantity　registered；　the　agreement　becomes　more　probable　than　if　tenths　were　the　smallest　quantities　noticed。　　In　general；　the　larger　the　lowest　unity　employed　the　greater　will　be　the　apparent　agreement　amongst　the　differences。　　Thus；　if；　in　the　transit　of　stars　near　the　pole；　the　times　of　passing　the　wires　were　only　registered　to　the　nearest　minute；　the　intervals　would　almost　certainly　be　equal。　　There　is　　another　circumstance；　about　which　there　is　some　difficulty。　　It　is　understood　that　the　same　instrument；the　thirty…inch　transit；　was　employed　by　Lieutenant　Foster；　and　it　has　not　been　stated　that　the　wires　were　changed；　although　this　has　most　probably　been　the　case。　　Now；　in　the　transits　which　the　later　observer　has　given；　he　has　found　it　necessary　to　correct　for　a　considerable　inequality　between　the　first　and　second　wires　（See　Phil。　Trans。　1827）。　　If　an　erroneous　impression　has　gone　abroad　on　this　subject；　it　is　doing　a　service　to　science　to　insure　its　correction；　by　drawing　attention　to　it。

Should　these　observations　be　confirmed　by　other　observers；　it　would　seem　to　follow　that　the　use　of　a　chronometer　renders　a　transit　more　exact；　and　therefore　that　it　ought　to　be　used　in　observatories。

Among　the　instruments　employed　by　Captain　Sabine；　was　a　repeating　circle　of　six　inches　diameter；　made　by　order　of　the　Board　of　Longitude；　for　the　express　purpose　of　ascertaining　how　far　repeating　instruments　might　be　diminished　in　size：a　most　important　subject；　on　which　the　Board　seem　to　have　entertained　a　very　commendable　degree　of　anxiety。

The　following　extract　from　the　〃Pendulum　Experiments〃　is　important：

〃The　repeating　circle　was　made　by　the　direction；　and　at　the　expense　of　the　Board　of　Longitude；　for　the　purpose　of　exemplifying　the　principle　of　repetition　when　applied　to　a　circle　of　so　small　a　diameter　as　six　inches；　carrying　a　telescope　of　seven　inches　focal　length；　and　one　inch　aperture；　and　of　practically　ascertaining　the　degree　of　accuracy　which　might　be　retained；　whilst　the　portability　of　the　instrument　should　be　increased；　by　a　reduction　in　the　size　to　half　the　amount　which　had　been　previously　regarded　by　the　most　eminent　artists　as　the　extreme　limit　of　diminution　to　which　repeating　circles；　designed　for　astronomical　purposes；　ought　to　be　carried。

〃The　practical　value　of　the　six…inch　repeating　circle　may　be　estimated；　by　comparing　the　differences　of　the　partial　results　from　the　mean　at　each　station；　with　the　correspondence　of　any　similar　collection　of　observations　made　with　a　circle；　on　the　original　construction；　and　of　large　dimensions；　such；　for　instance；　as　the　latitudes　of　the　stations　of　the　French　are；　recorded　in　the　Base　du　Systeme　Metrique：　　when；　if　due　allowance　be　made　for　the　extensive　experience　and　great　skill　of　the　distinguished　persons　who　conducted　the　French　observations；　the　comparison　will　scarcely　appear　to　the　disadvantage　of　the　smaller　circle；　even　if　extended　generally　through　all　the　stations　of　the　present　volume；　but　if　it　be　particularly　directed　to　Maranham　and　Spitzbergen；at　which　stations　the　partial　results　were　more　numerous　than　elsewhere；　and　obtained　with　especial　regard　to　every　circumstance　by　which　their　accuracy　might　be　affected；　the　performance　of　the　six…inch　circle　will　appear　fully　equal　to　that