In　confirmation　of　this　may　be　adduced　the　opinion　of　the　late　M。　Delambre；　which　is　the　more　important；　from　the　statement　it　contains　relative　to　the　necessity　of　publishing　all　the　observations　which　have　been　made。
  〃Mais　quelque　soit　le　parti　que　l'on　prefere；　il　me　semble　qu'on　doit　tout　publier。　　Ces　irregularites　memes　sont　des　faits　qu'il　importe　de　connoitre。　　LES　SOINS　LES　PLUS　ATTENTIFS　N'EN　SAUROIENT　PRESERVER　LES　OBSERVATEURS　LES　PLUS　EXERCES；　et　celui　qui　ne　produiroit　que　des　angles　toujours　parfaitment　d'accord　auroit　ete　singulierement　bien　servi　par　les　circonstances　ou　ne　seroit　pas　bien　sincere。〃BASE　DU　SYSTEME　METRIQUE；　Discours　Preliminaire；　p。　158。
  This　desire　for　extreme　accuracy　has　called　away　the　attention　of　experimenters　from　points　of　far　greater　importance；　and　it　seems　to　have　been　too　much　overlooked　in　the　present　day；　that　genius　marks　its　tract；　not　by　the　observation　of　quantities　inappreciable　to　any　but　the　acutest　senses；　but　by　placing　Nature　in　such　circumstances；　that　she　is　forced　to　record　her　minutest　variations　on　so　magnified　a　scale；　that　an　observer；　possessing　ordinary　faculties；　shall　find　them　legibly　written。　He　who　can　see　portions　of　matter　beyond　the　ken　of　the　rest　of　his　species；　confers　an　obligation　on　them；　by　recording　what　he　sees；　but　their　knowledge　depends　both　on　his　testimony　and　on　his　judgment。　　He　who　contrives　a　method　of　rendering　such　atoms　visible　to　ordinary　observers；　communicates　to　mankind　an　instrument　of　discovery；　and　stamps　his　own　observations　with　a　character；　alike　independent　of　testimony　or　of　judgment。
  SECTION　2。
  ON　THE　ART　OF　OBSERVING。
  The　remarks　in　this　section　are　not　proposed　for　the　assistance　of　those　who　are　already　observers；　but　are　intended　to　show　to　persons　not　familiar　with　the　subject；　that　in　observations　demanding　no　unrivalled　accuracy；　the　principles　of　common　sense　may　be　safely　trusted；　and　that　any　gentleman　of　liberal　education　may；　by　perseverance　and　attention；　ascertain　the　limits　within　which　he　may　trust　both　his　instrument　and　himself。
  If　the　instrument　is　a　divided　one；　the　first　thing　is　to　learn　to　read　the　verniers。　　If　the　divisions　are　so　fine　that　the　coincidence　is　frequently　doubtful；　the　best　plan　will　be　for　the　learner　to　get　some　acquaintance　who　is　skilled　in　the　use　of　instruments；　and　having　set　the　instrument　at　hazard；　to　write　down　the　readings　of　the　verniers；　and　then　request　his　friend　to　do　the　same；　whenever　there　is　any　difference；　he　should　carefully　examine　the　doubtful　one；　and　ask　his　friend　to　point　out　the　minute　peculiarities　on　which　he　founds　his　decision。　This　should　be　repeated　frequently；　and　after　some　practice；　he　should　note　how　many　times　in　a　hundred　his　reading　differs　from　his　friend's；　and　also　how　many　divisions　they　usually　differ。
  The　next　point　is；　to　ascertain　the　precision　with　which　the　learner　can　bisect　an　object　with　the　wires　of　the　telescope。　This　can　be　done　without　assistance。　　It　is　not　necessary　even　to　adjust　the　instrument；　but　merely　to　point　it　to　a　distant　object。　　When　it　bisects　any　remarkable　point；　read　off　the　verniers；　and　write　down　the　result；　then　displace　the　telescope　a　little；　and　adjust　it　again。　　A　series　of　such　observations　will　show　the　confidence　which　is　due　to　the　observer's　eye　in　bisecting　an　object；　and　also　in　reading　the　verniers；　and　as　the　first　direction　gave　him　some　measure　of　the　latter；　he　may；　in　a　great　measure；　appreciate　his　skill　in　the　former。　　He　should　also；　when　he　finds　a　deviation　in　the　reading；　return　to　the　telescope；　and　satisfy　himself　if　he　has　made　the　bisection　as　complete　as　he　can。　　In　general；　the　student　should　practise　each　adjustment　separately；　and　write　down　the　results　wherever　he　can　measure　its　deviations。
  Having　thus　practised　the　adjustments；　the　next　step　is　to　make　an　observation；　but　in　order　to　try　both　himself　and　the　instrument；　let　him　take　the　altitude　of　some　fixed　object；　a　terrestrial　one；　and　having　registered　the　result；　let　him　derange　the　adjustment；　and　repeat　the　process　fifty　or　a　hundred　times。　　This　will　not　merely　afford　him　excellent　practice；　but　enable　him　to　judge　of　his　own　skill。
  The　first　step　in　the　use　of　every　instrument；　is　to　find　the　limits　within　which　its　employer　can　measure　the　SAME　OBJECT　UNDER　THE　SAME　CIRCUMSTANCES。　　It　is　only　from　a　knowledge　of　this；　that　he　can　have　confidence　in　his　measures　of　the　SAME　OBJECT　UNDER　DIFFERENT　CIRCUMSTANCES；　and　after　that；　of　DIFFERENT　OBJECTS　UNDER　DIFFERENT　CIRCUMSTANCES。
  These　principles　are　applicable　to　almost　all　instruments。　　If　a　person　is　desirous　of　ascertaining　heights　by　a　mountain　barometer；　let　him　begin　by　adjusting　the　instrument　in　his　own　study；　and　having　made　the　upper　contact；　let　him　write　down　the　reading　of　the　vernier；　and　then　let　him　derange　the　UPPER　adjustment　ONLY；　re…adjust；　and　repeat　the　reading。　　When　he　is　satisfied　about　the　limits　within　which　he　can　make　that　adjustment；　let　him　do　the　same　repeatedly　with　the　lower；　but　let　him　not；　until　he　knows　his　own　errors　in　reading　and　adjusting；　pronounce　upon　those　of　the　instrument。　　In　the　case　of　a　barometer；　he　must　also　be　assured；　that　the　temperature　of　the　mercury　does　not　change　during　the　interval。
  A　friend　once　brought　to　me　a　beautifully　constructed　piece　of　mechanism；　for　marking　minute　portions　of　time；　the　three…　hundredth　parts　of　a　second　were　indicated　by　it。　　It　was　a　kind　of　watch；　with　a　pin　for　stopping　one　of　the　hands。　I　proposed　that　we　should　each　endeavour　to　stop　it　twenty　times　in　succession；　at　the　same　point。　　We　were　both　equally　unpractised；　and　our　first　endeavours　showed　that　we　could　not　be　confident　of　the　twentieth　part　of　a　second。　In　fact；　both　the　time　occupied　in　causing　the　extremities　of　the　fingers　to　obey　the　volition；　as　well　as　the　time　employed　in　compressing　the　flesh　before　the　fingers　acted　on　the　stop；　appeared　to　influence　the　accuracy　of　our　observations。　From　some　few　experiments　I　made；　I　thought　I　perceived　that　the　rapidity　of　the　transmission　of　the　effects　of　the　will；　depended　on　the　state　of　fatigue　or　health　of　the　body。　If　any　one　were　to　make　experiments　on　this　subject；　it　might　be　interesting；　to　compare　the　rapidity　of　the　transmission　of　volition　in　different　persons；　with　the　time　occupied　in　obliterating　an　impression　made　on　one　of　the　senses　of　the　same　persons。　　For　example；　by　having　a　mechanism　to　make　a　piece　of　ignited　charcoal　revolve　with　different　degrees　of　velocity；　some　persons　will　perceive　a　continuous　circle　of　light　before　others；　whose　retina　does　not　retain　so　long　impressions　that　are　made　upon　it。
  SECTION　3。
  ON　THE　FRAUDS　OF　OBSERVERS。
  Scientific　inquiries　are　more　exposed　than　most　others　to　the　inroads　of　pretenders；　and　I　feel　that　I　shall　deserve　the　thanks　of　all　who　really　value　truth；　by　stating　some　of　the　methods　of　deceiving　practised　by　unworthy　claimants　for　its　honours；　whilst　the　mere　circumstance　of　their　arts　being　known　may　deter　future　offenders。
  There　are　several　species　of　impositions　that　have　been　practised　in　science；　which　are　but　little　known；　except　to　the　initiated；　and　which　it　may　perhaps　be　possible　to　render　quite　intelligible　to　ordinary　understandings。　　These　may　be　classed　under　the　heads　of　hoaxing；　forging；　trimming；　and　cooking。
  OF　HOAXING。　　This；　perhaps；　will　be　better　explained　by　an　example。　　In　the　year　1788；　M。　Gioeni；　a　knight　of　Malta；　published　at　Naples　an　account　of　a　new　family　of　Testacea；　of　which　he　described；　with　great　minuteness；　one　species；　the　specific　name　of　which　has　been　taken　from　its　habitat；　and　the　generic　he　took　from　his　own　family；　calling　it　Gioenia　Sicula。　It　consisted　of　two　rounded　triangular　valves；　united　by　the　body　of　the　animal　to　a　smaller　valve　in　front。　　He　gave　figures　of　the　animal；　and　of　its　parts；　described　its　structure；　its　mode　of　advancing　along　the　sand；　the　figure　of　the　tract　it　left；　and　estimated　the　velocity　of　its　course　at　about　two…thirds　of　an　inch　per　minute。　　He　then　described　the　structure　of　the　shell；　which　he　treated　with　nitric　acid；　and　found　it　approach　nearer　to　the　nature　of　bone　than　any　other　shell。
  The　editors　of　the　ENCYCLOPEDIE　METHODIQUE；　have　copied　this　description；　and　have　given　figures　of　the　Gioenia　Sicula。　　The　fact；　however；　is；　that　no　such　animal　exists；　but　that　the　knight　of　Malta；　finding　on　the　Sicilian　shores　the　three　internal　bones　of　one　of　the　species　of　Bulla；　of　which　some　are　found　on　the　south…western　coast　of　England；　＇Bulla　lignaria＇　described　and　figured　these　bones　most　accurately；　and　drew　the　whole　of　the　rest　of　the　description　from　the　stores　of　his　own　imagination。
  Such　frauds　are　far　from　justifiable；　the　only　excuse　which　has　been　made　for　them　is；　when　they　have　been　practised　on　scientific　academies　which　had　reached　the　period　of　dotage。　　It　should　however　be　remembered；　that　the　productions　of　nature　are　so　various；　that　mere　strangeness　is　very　far　from　sufficient　to　render　doubtful　the　existence　of　any　creature　for　which　there　is　evidence；　　＇The　number　of　vertebrae　in　the　neck　of　the　plesiosaurus　is　a　strange　but　ascertained　fact