Asyetnoonehaddiscoveredthatelectricitycouldbestored，orgeneratedinanywayotherthanbysomefrictiondevice。Butverysoontwoexperimenters，DeanvonKleist，ofCamin，Pomerania，andPietervanMusschenbroek，thefamousteacherofLeyden，apparentlyindependently，madethediscoveryofwhathasbeenknowneversinceastheLeydenjar。AndalthoughMusschenbroekissometimescreditedwithbeingthediscoverer，therecanbenodoubtthatVonKleist’sdiscoveryantedatedhisbyafewmonthsatleast。
　　VonKleistfoundthatbyadevicemadeofanarrow-neckedbottlecontainingalcoholormercury，intowhichanironnailwasinserted，bewasabletoretainthechargeofelectricity，afterelectrifyingthisapparatuswiththefrictionalmachine。Hemadealsoasimilardevice，morecloselyresemblingthemodernLeydenjar，fromathermometertubepartlyfilledwithwaterandawiretippedwithaballoflead。Withthesedeviceshefoundthathecouldretainthechargeofelectricityforseveralhours，andcouldproducetheusualelectricalmanifestations，eventoignitingspirits，quiteaswellaswiththefrictionalmachine。
　　TheseexperimentswerefirstmadeinOctober，1745，andafteramonthoffurtherexperimenting，VonKleistsentthefollowingaccountofthemtoseveraloftheleadingscientists，amongothers，Dr。Lieberkuhn，inBerlin，andDr。Kruger，ofHalle。
　　"Whenanail，orapieceofthickbrasswire，isputintoasmallapothecary’sphialandelectrified，remarkableeffectsfollow；
　　butthephialmustbeverydry，orwarm。IcommonlyrubitoverbeforehandwithafingeronwhichIputsomepoundedchalk。Ifalittlemercuryorafewdropsofspiritofwinebeputintoit，theexperimentsucceedsbetter。Assoonasthisphialandnailareremovedfromtheelectrifying-glass，ortheprimeconductor，towhichithasbeenexposed，istakenaway，itthrowsoutapencilofflamesolongthat，withthisburningmachineinmyhand，Ihavetakenabovesixtystepsinwalkingaboutmyroom。
　　Whenitiselectrifiedstrongly，Icantakeitintoanotherroomandtherefirespiritsofwinewithit。IfwhileitiselectrifyingIputmyfinger，orapieceofgoldwhichIholdinmyhand，tothenail，Ireceiveashockwhichstunsmyarmsandshoulders。
　　"Atintube，oraman，placeduponelectrics，iselectrifiedmuchstrongerbythismeansthaninthecommonway。WhenIpresentthisphialandnailtoatintube，whichIhave，fifteenfeetlong，nothingbutexperiencecanmakeapersonbelievehowstronglyitiselectrified。Iampersuaded，"headds，"thatinthismannerMr。Bosewouldnothavetakenasecondelectricalkiss。Twothinglasseshavebeenbrokenbytheshockofit。Itappearstomeveryextraordinary，thatwhenthisphialandnailareincontactwitheitherconductingornon-conductingmatter，thestrongshockdoesnotfollow。Ihavecementedittowood，metal，glass，sealing-wax，etc。，whenIhaveelectrifiedwithoutanygreateffect。Thehumanbody，therefore，mustcontributesomethingtoit。ThisopinionisconfirmedbymyobservingthatunlessIholdthephialinmyhandIcannotfirespiritsofwinewithit。"[2]
　　ButitseemsthatnoneofthemenwhosawthisaccountwereabletorepeattheexperimentandproducetheeffectsclaimedbyVonKleist，andprobablyforthisreasonthediscoveryoftheobscurePomeranianwasforatimelostsightof。
　　Musschenbroek’sdiscoverywasmadewithinashorttimeafterVonKleist’s——infact，onlyamatterofabouttwomonthslater。Butthedifferenceinthereputationsofthetwodiscoverersinsuredaverydifferentreceptionfortheirdiscoveries。MusschenbroekwasoneoftheforemostteachersofEurope，andsowidelyknownthatthegreatuniversitiesviedwitheachother，andkingswerebidding，forhisservices。Naturally，anydiscoverymadebysuchafamouspersonwouldsoonbeheraldedfromoneendofEuropetotheother。AndsowhenthisprofessorofLeydenmadehisdiscovery，theapparatuscametobecalledthe"Leydenjar，"forwantofabettername。TherecanbelittledoubtthatMusschenbroekmadehisdiscoveryentirelyindependentlyofanyknowledgeofVonKleist’s，or，forthatmatter，withouteverhavingheardofthePomeranian，andhisactionsinthematterareentirelyhonorable。
　　Hisdiscoverywastheresultofanaccident。Whileexperimentingtodeterminethestrengthofelectricityhesuspendedagun-barrel，whichhechargedwithelectricityfromarevolvingglassglobe。Fromtheendofthegun-barreloppositetheglobewasabrasswire，whichextendedintoaglassjarpartlyfilledwithwater。Musschenbroekheldinonehandthisjar，whilewiththeotherheattemptedtodrawsparksfromthebarrel。Suddenlyhereceivedashockinthehandholdingthejar，that"shookhimlikeastrokeoflightning，"andforamomentmadehimbelievethat"hewasdonefor。"Continuinghisexperiments，nevertheless，hefoundthatifthejarwereplacedonapieceofmetalonthetable，ashockwouldbereceivedbytouchingthispieceofmetalwithonehandandtouchingthewirewiththeother——thatis，apathwasmadefortheelectricaldischargethroughthebody。ThiswaspracticallythesameexperimentasmadebyVonKleistwithhisbottleandnail，butcarriedonestepfarther，asitshowedthatthe"jar"neednotnecessarilybeheldinthehand，asbelievedbyVonKleist。Furtherexperiments，continuedbymanyphilosophersatthetime，revealedwhatVonKleisthadalreadypointedout，thattheelectrifiedjarremainedchargedforsometime。
　　SoonafterthisDanielGralath，wishingtoobtainstrongerdischargesthancouldbehadfromasingleLeydenjar，conceivedtheideaofcombiningseveraljars，thusforthefirsttimegroupingthegeneratorsina"battery"whichproducedadischargestrongenoughtokillbirdsandsmallanimals。Healsoattemptedtomeasurethestrengthofthedischarges，butsoongaveitupindespair，andthesolutionofthisproblemwasleftforlatenineteenth-centuryscientists。
　　TheadventoftheLeydenjar，whichmadeitpossibletoproducestrongelectricaldischargesfromasmallandcomparativelysimpledevice，wasfollowedbymorespectaculardemonstrationsofvariouskindsalloverEurope。Theseexhibitionsarousedtheinterestofthekingsandnoblemen，sothatelectricitynolongerremaineda"playthingofthephilosophers"alone，butofkingsaswell。Afavoritedemonstrationwasthatofsendingtheelectricaldischargethroughlonglinesofsoldierslinkedtogetherbypiecesofwire，thedischargecausingthemto"springintotheairsimultaneously"inamostastonishingmanner。AcertainmonkinParispreparedamostelaborateseriesofdemonstrationsfortheamusementoftheking，amongotherthingslinkingtogetheranentireregimentofninehundredmen，causingthemtoperformsimultaneousspringsandcontortionsinamannermostamusingtotheroyalguests。Butnotalltheexperimentsbeingmadewereofapurelyspectacularcharacter，althoughmostofthemaccomplishedlittleexceptinanegativeway。ThefamousAbbeNollet，forexample，combinedusefulexperimentswithspectaculardemonstrations，thuskeepinguppopularinterestwhileaidingthecauseofscientificelectricity。
　　WILLIAMWATSON
　　Naturally，thenewdiscoveriesmadenecessaryanewnomenclature，newwordsandelectricaltermsbeingconstantlyemployedbythevariouswritersofthatday。AmongthesewriterswastheEnglishscientistWilliamWatson，whowasnotonlyamostprolificwriterbutatirelessinvestigator。Manyofthewordscoinedbyhimarenowobsolete，butoneatleast，"circuit，"stillremainsinuse。
　　In1746，aFrenchscientist，LouisGuillaumeleMonnier，badmadeacircuitincludingmetalandwaterbylayingachainhalf-wayaroundtheedgeofapond，amanateitherendholdingit。Oneofthesemendippedhisfreehandinthewater，theotherpresentingaLeydenjartoarodsuspendedonacorkfloatonthewater，bothmenreceivingashocksimultaneously。Watson，ayearlater，attemptedthesameexperimentonalargerscale。HelaidawireabouttwelvehundredfeetlongacrossWestminsterBridgeovertheThames，bringingtheendstothewater’sedgeontheoppositebanks，amanatoneendholdingthewireandtouchingthewater。
　　AsecondmanontheoppositesideheldthewireandaLeydenjar；
　　andathirdtouchedthejarwithonehand，whilewiththeotherhegraspedawirethatextendedintotheriver。Inthiswaytheynotonlyreceivedtheshock，butfiredalcoholasreadilyacrossthestreamascouldbedoneinthelaboratory。InthisexperimentWatsondiscoveredthesuperiorityofwireoverchainasaconductor，rightlyascribingthissuperioritytothecontinuityofthemetal。
　　Watsoncontinuedmakingsimilarexperimentsoverlongerwatercourses，someofthemaslongaseightthousandfeet，andwhileengagedinmakingoneofthesehemadethediscoverysoessentialtolaterinventions，thattheearthcouldbeusedaspartofthecircuitinthesamemannerasbodiesofwater。
　　Lengtheninghiswireshecontinuedhisexperimentsuntilacircuitoffourmileswasmade，andstilltheelectricityseemedtotraversethecourseinstantaneously，andwithapparentlyundiminishedforce，iftheinsulationwasperfect。
　　BENJAMINFRANKLIN
　　Watson’swritingsnowcarriedthefieldofactivediscoveryacrosstheAtlantic，andforthefirsttimeanAmericanscientistappeared——ascientistwhonotonlyrivalled，butexcelled，hisEuropeancontemporaries。BenjaminFranklin，ofPhiladelphia，comingintopossessionofsomeofWatson’sbooks，becamesointerestedintheexperimentsdescribedinthemthathebeganatonceexperimentingwithelectricity。InWatson’sbookweregivendirectionsformakingvariousexperiments，andtheseassistedFranklininrepeatingtheoldexperiments，andeventuallyaddingnewones。AssociatedwithFranklin，andequallyinterestedandenthusiastic，ifnotequallysuccessfulinmakingdiscoveries，werethreeothermen，ThomasHopkinson，PhilipSing，andEbenezerKinnersley。Thesemenworkedtogetherconstantly，althoughitappearstohavebeenFranklinwhomadeindependentlytheimportantdiscoveries，andformulatedthefamousFrankliniantheory。
　　Workingsteadily，andkeepingconstantlyintouchwiththeprogressoftheEuropeaninvestigators，Franklinsoonmadesomeexperimentswhichhethoughtdemonstratedsomehithertounknownphasesofelectricalmanifestation。Thiswastheeffectofpointedbodies"inDRAWINGOFFandTHROWINGOFFtheelectricalfire。"Inhisdescriptionofthisphenomenon，Franklinwrites:
　　"Placeanironshotofthreeorfourinchesdiameteronthemouthofaclean，dry，glassbottle。Byafinesilkenthreadfromtheceilingrightoverthemouthofthebottle，suspendasmallcorkball，aboutthebignessofamarble；thethreadofsuchalengththatthecorkballmayrestagainstthesideoftheshot。
　　Electrifytheshot，andtheballwillberepelledtothedistanceoffourorfiveinches，moreorless，accordingtothequantityofelectricity。Wheninthisstate，ifyoupresenttotheshotthepointofalong，slendershaft-bodkin，atsixoreightinchesdistance，therepellencyisinstantlydestroyed，andthecorkfliestotheshot。Abluntbodymustbebroughtwithinaninch，anddrawaspark，toproducethesameeffect。
　　"ToprovethattheelectricalfireisDRAWNOFFbythepoint，ifyoutakethebladeofthebodkinoutofthewoodenhandleandfixitinastickofsealing-wax，andthenpresentitatthedistanceaforesaid，orifyoubringitverynear，nosucheffectfollows；
　　butslidingonefingeralongthewaxtillyoutouchtheblade，andtheballfliestotheshotimmediately。Ifyoupresentthepointinthedarkyouwillsee，sometimesatafootdistance，andmore，alightgatheruponitlikethatofafire-flyorglow-worm；thelesssharpthepoint，theneareryoumustbringittoobservethelight；andatwhateverdistanceyouseethelight，youmaydrawofftheelectricalfireanddestroytherepellency。
　　Ifacorkballsosuspendedberepelledbythetube，andapointbepresentedquicktoit，thoughataconsiderabledistance，’tissurprisingtoseehowsuddenlyitfliesbacktothetube。Pointsofwoodwilldoaswellasthoseofiron，providedthewoodisnotdry；forperfectlydrywoodwillnomoreconductelectricitythansealing-wax。
　　"ToshowthatpointswillTHROWOFFaswellasDRAWOFFtheelectricalfire，layalong，sharpneedleupontheshot，andyoucannotelectrifytheshotsoastomakeitrepelthecorkball。
　　Orfixaneedletotheendofasuspendedgun-barrelorironrod，soastopointbeyonditlikealittlebayonet，andwhileitremainsthere，thegun-barrelorrodcannot，byapplyingthetubetotheotherend，beelectrifiedsoastogiveaspark，thefirecontinuallyrunningoutsilentlyatthepoint。Inthedarkyoumayseeitmakethesameappearanceasitdoesinthecasebeforementioned。"[3]
　　VonGuericke，Hauksbee，andGrayhadnoticedthatpointedbodiesattractedelectricityinapeculiarmanner，butthisdemonstrationofthe"drawingoff"of"electricalfire"wasoriginalwithFranklin。Originalalsowasthetheorythathenowsuggested，whichhadatleastthemeritofbeingthinkableevenbynon-philosophicalminds。Itassumesthatelectricityislikeafluid，thatwillflowalongconductorsandaccumulateinproperreceptacles，verymuchasordinaryfluidsdo。Thisconceptionisprobablyentirelyincorrect，butneverthelessitislikelytoremainapopularone，atleastoutsideofscientificcircles，oruntilsomethingequallytangibleissubstituted。
　　FRANKLIN’STHEORYOFELECTRICITY
　　AccordingtoFranklin’stheory，electricityexistsinallbodiesasa"commonstock，"andtendstoseekandremaininastateofequilibrium，justasfluidsnaturallytendtoseekalevel。Butitmay，nevertheless，beraisedorlowered，andthisequilibriumbethusdisturbed。IfabodyhasmoreelectricitythanitsnormalamountitissaidtobePOSITIVELYelectrified；butifithasless，itisNEGATIVELYelectrified。Anover-electrifiedor"plus"
　　bodytendstogiveitssurplusstocktoabodycontainingthenormalamount；whilethe"minus"orunder-electrifiedbodywilldrawelectricityfromonecontainingthenormalamount。
　　Workingalonglinessuggestedbythistheory，Franklinattemptedtoshowthatelectricityisnotcreatedbyfriction，butsimplycollectedfromitsdiversifiedstate，therubbedglassglobeattractingacertainquantityof"electricalfire，"buteverreadytogiveituptoanybodythathasless。HeexplainedthechargedLeydenjarbyshowingthattheinnercoatingoftin-foilreceivedmorethantheordinaryquantityofelectricity，andinconsequenceisPOSITIVELYelectrified，whiletheoutercoating，havingtheordinaryquantityofelectricitydiminished，iselectrifiedNEGATIVELY。
　　ThesestudiesoftheLeydenjar，andthestudiesofpiecesofglasscoatedwithsheetmetal，ledFranklintoinventhisbattery，constructedofelevenlargeglassplatescoatedwithsheetsoflead。Withthismachine，afterovercomingsomedefects，hewasabletoproduceelectricalmanifestationsofgreatforce——aforcethat"knewnobounds，"ashedeclared"exceptinthematterofexpenseandoflabor"，andwhichcouldbemadetoexceed"thegreatestknoweffectsofcommonlightning。"
　　ThisreferencetolightningwouldseemtoshowFranklin’sbelief，evenatthattime，thatlightningiselectricity。Manyeminentobservers，suchasHauksbee，Wall，Gray，andNollet，hadnoticedtheresemblancebetweenelectricsparksandlightning，butnoneofthesehadmorethansurmisedthatthetwomightbeidentical。
　　In1746，thesurgeon，JohnFreke，alsoassertedhisbeliefinthisidentity。Winkler，shortlyafterthistime，expressedthesamebelief，and，assumingthattheywerethesame，declaredthat"thereisnoproofthattheyareofdifferentnatures"；andstillhedidnotprovethattheywerethesamenature。
　　FRANKLININVENTSTHELIGHTNING-ROD
　　EvenbeforeFranklinprovedconclusivelythenatureoflightning，hisexperimentsindrawingofftheelectricchargewithpointsledtosomepracticalsuggestionswhichresultedintheinventionofthelightning-rod。IntheletterofJuly，1750，whichhewroteonthesubject，hegavecarefulinstructionsastothewayinwhichtheserodsmightbeconstructed。InpartFranklinwrote:
　　"Maynottheknowledgeofthispowerofpointsbeofusetomankindinpreservinghouses，churches，ships，etc。，fromthestrokeoflightningbydirectingustofixonthehighestpartsoftheedificesuprightrodsofironmadesharpasaneedle，andgilttopreventrusting，andfromthefootoftheserodsawiredowntheoutsideofthebuildingintothegrounds，ordownroundoneoftheshroudsofashipanddownhersidetillitreachesthewater？Wouldnotthesepointedrodsprobablydrawtheelectricalfiresilentlyoutofacloudbeforeitcamenighenoughtostrike，andtherebysecureusfromthatmostsuddenandterriblemischief？
　　"Todeterminethisquestion，whetherthecloudsthatcontainthelightningareelectrifiedornot，Iproposeanexperimenttobetriedwhereitmaybedoneconveniently。Onthetopofsomehightowerorsteeple，placeakindofsentry-box，bigenoughtocontainamanandanelectricalstand。Fromthemiddleofthestandletanironrodriseandpass，bendingoutofthedoor，andthenuprighttwentyorthirtyfeet，pointedverysharpattheend。Iftheelectricalstandbekeptcleananddry，amanstandingonitwhensuchcloudsarepassinglowmightbeelectrifiedandaffordsparks，theroddrawingfiretohimfromacloud。IfanydangertothemanbeapprehendedthoughIthinktherewouldbenone，lethimstandonthefloorofhisboxandnowandthenbringneartotherodtheloopofawirethathasoneendfastenedtotheleads，heholdingitbyawaxhandle；sothesparks，iftherodiselectrified，willstrikefromtherodtothewireandnoteffecthim。"[4]
　　Notsatisfiedwithalltheevidencethathehadcollectedpointingtotheidentityoflightningandelectricity，headdsonemorestrikingandverysuggestivepieceofevidence。
　　Lightningwasknownsometimestostrikepersonsblindwithoutkillingthem。Inexperimentingonpigeonsandpulletswithhiselectricalmachine，Franklinfoundthatafowl，whennotkilledoutright，wassometimesrenderedblind。ThereportoftheseexperimentswereincorporatedinthisfamousletterofthePhiladelphiaphilosopher。
　　TheattitudeoftheRoyalSocietytowardsthisclearlystatedletter，withitsusefulsuggestions，mustalwaysremainasablotontherecordofthisusuallyveryreceptiveandliberal-mindedbody。Farfrompublishingitorreceivingitatall，theyderidedthewholematterastoovisionaryfordiscussionbythesociety。
　　Howwasitpossiblethatanygreatscientificdiscoverycouldbemadebyaself-educatedcolonialnewspapereditor，whoknewnothingofEuropeanscienceexceptbyhearsay，whenallthegreatscientificmindsofEuropehadfailedtomakethediscovery？Howindeed！AndyetitwouldseemthatifanyoftheinfluentialmembersofthelearnedsocietyhadtakenthetroubletoreadoverFranklin’sclearlystatedletter，theycouldhardlyhavefailedtoseethathissuggestionswereworthyofconsideration。Butatallevents，whethertheydidordidnotmatterslittle。Thefactremainsthattheyrefusedtoconsiderthepaperseriouslyatthetime；andlateron，whenitstruevaluebecameknown，wereobligedtoacknowledgetheirerrorbyatardyreportonthealreadywell-knowndocument。
　　ButifEnglishscientistswerecoldintheirreceptionofFranklin’stheoryandsuggestions，theFrenchscientistswerenot。Buffon，perceivingatoncetheimportanceofsomeofFranklin’sexperiments，tookstepstohavethefamouslettertranslatedintoFrench，andsoonnotonlythesavants，butmembersofthecourtandthekinghimselfwereintenselyinterested。Twoscientists，DeLorandD’Alibard，undertooktotestthetruthofFranklin’ssuggestionsastopointedrods"drawingofflightning。"InagardennearParis，thelattererectedapointedironrodfiftyfeethighandaninchindiameter。Asnothunder-cloudsappearedforseveraldays，aguardwasstationed，armedwithaninsulatedbrasswire，whowasdirectedtotesttheironrodswithitincaseastormcameonduringD’Alibard’sabsence。Thestormdidcomeon，andtheguard，notwaitingforhisemployer’sarrival，seizedthewireandtouchedtherod。Instantlytherewasareport。Sparksflewandtheguardreceivedsuchashockthathethoughthistimehadcome。Believingfromhisoutcrythathewasmortallyhurt，hisfriendsrushedforaspiritualadviser，whocamerunningthroughrainandhailtoadministerthelastrites；butwhenhefoundtheguardstillaliveanduninjured，heturnedhisvisittoaccountbytestingtherodhimselfseveraltimes，andlaterwritingareportofhisexperimentstoM。d’Alibard。ThisscientistatoncereportedtheaffairtotheFrenchAcademy，remarkingthat"Franklin’sideawasnolongeraconjecture，butareality。"
　　FRANKLINPROVESTHATLIGHTNINGISELECTRICITY
　　Europe，hithertosomewhatscepticalofFranklin’sviews，wasbythistimeconvincedoftheidentityoflightningandelectricity。
　　ItwasnowFranklin’sturntobesceptical。Tohimthefactthatarod，onehundredfeethigh，becameelectrifiedduringastormdidnotnecessarilyprovethatthestorm-cloudswereelectrified。
　　Arodofthatlengthwasnotreallyprojectedintothecloud，forevenaverylowthunder-cloudwasmorethanahundredfeetabovetheground。Irrefutableproofcouldonlybehad，ashesawit，by"extracting"thelightningwithsomethingactuallysentupintothestorm-cloud；andtoaccomplishthisFranklinmadehissilkkite，withwhichhefinallydemonstratedtohisownandtheworld’ssatisfactionthathistheorywascorrect。
　　Takinghiskiteoutintoanopencommonontheapproachofathunder-storm，heflewitwellupintothethreateningclouds，andthen，touching，thesuspendedkeywithhisknuckle，receivedtheelectricspark；andalittlelaterhechargedaLeydenjarfromtheelectricitydrawnfromthecloudswithhiskite。
　　Inabriefbutdirectletter，hesentanaccountofhiskiteandhisexperimenttoEngland:
　　"Makeasmallcrossoftwolightstripsofcedar，"hewrote，"thearmssolongastoreachtothefourcornersofalarge，thin，silkhandkerchiefwhenextended；tiethecornersofthehandkerchieftotheextremitiesofthecrosssoyouhavethebodyofakite；whichbeingproperlyaccommodatedwithatail，loop，andstring，willriseintheairlikethosemadeofpaper；butthisbeingofsilkisfittertobearthewindandwetofathunder-gustwithouttearing。Tothetopoftheuprightstickofthecrossistobefixedaverysharp-pointedwire，risingafootormoreabovethewood。Totheendofthetwine，nextthehand，istobetiedasilkribbon；wherethesilkandtwinejoinakeymaybefastened。Thiskiteistoberaisedwhenathunder-gustappearstobecomingon，andthepersonwhoholdsthestringmuststandwithinadoororwindoworundersomecover，sothatthesilkribbonmaynotbewet；andcaremustbetakenthatthetwinedoesnottouchtheframeofthedoororwindow。Assoonasanyofthethunder-cloudscomeoverthekite，thepointedwirewilldrawtheelectricfirefromthem，andthekite，withallthetwine，willbeelectrifiedandtheloosefilamentswillstandouteverywhereandbeattractedbytheapproachingfinger，andwhentherainhaswetthekiteandtwinesothatitcanconducttheelectricfirefreely，youwillfinditstreamoutplentifullyfromthekeyontheapproachofyourknuckle，andwiththiskeythephialmaybecharged；andfromelectricfirethusobtainedspiritsmaybekindledandallotherelectricexperimentsperformedwhichareusuallydonebythehelpofarubbedglassglobeortube，andtherebythesamenessoftheelectricmatterwiththatoflightningcompletelydemonstrated。"[5]
　　InexperimentingwithlightningandFranklin’spointedrodsinEurope，severalscientistsreceivedsevereshocks，inonecasewithafatalresult。ProfessorRichman，ofSt。Petersburg，whileexperimentingduringathunder-storm，withanironrodwhichhehaderectedonhishouse，receivedashockthatkilledhiminstantly。
　　About1733，aswehaveseen，Dufayhaddemonstratedthatthereweretwoapparentlydifferentkindsofelectricity；onecalledVITREOUSbecauseproducedbyrubbingglass，andtheotherRESINOUSbecauseproducedbyrubbedresinousbodies。Dufaysupposedthatthesetwoapparentlydifferentelectricitiescouldonlybeproducedbytheirrespectivesubstances；buttwentyyearslater，JohnCanton1715-1772，anEnglishman，demonstratedthatundercertainconditionsbothmightbeproducedbyrubbingthesamesubstance。Canton’sexperiment，madeuponaglasstubewitharoughenedsurface，provedthatifthesurfaceofthetubewererubbedwithoiledsilk，vitreousorpositiveelectricitywasproduced，butifrubbedwithflannel，resinouselectricitywasproduced。Hediscoveredstillfurtherthatbothkindscouldbeexcitedonthesametubesimultaneouslywithasinglerubber。Todemonstratethisheusedatube，one-halfofwhichhadaroughenedtheotheraglazedsurface。Withasinglestrokeoftherubberhewasabletoexcitebothkindsofelectricityonthistube。Hefoundalsothatcertainsubstances，suchasglassandamber，wereelectrifiedpositivelywhentakenoutofmercury，andthisledtohisimportantdiscoverythatanamalgamofmercuryandtin，whenusedonthesurfaceoftherubber，wasveryeffectiveinexcitingglass。
　　XV。NATURALHISTORYTOTHETIMEOFLINNAeUS
　　ModernsystematicbotanyandzoologyareusuallyheldtohavetheirbeginningswithLinnaeus。ButtherewerecertainprecursorsofthefamousSwedishnaturalist，someofthemantedatinghimbymorethanacentury，whoseworkmustnotbealtogetherignored——suchmenasKonradGesner1516-1565，AndreasCaesalpinus1579-1603，FranciscoRedi1618-1676，GiovanniAlfonsoBorelli1608-1679，JohnRay1628-1705，RobertHooke1635-1703，JohnSwammerdam1637-1680，MarcelloMalpighi1628-1694，NehemiahGrew1628-1711，JosephTournefort1656-1708，RudolfJacobCamerarius1665-1721，andStephenHales1677-1761。Thelastnamedofthesewas，tobesure，acontemporaryofLinnaeushimself，butGesnerandCaesalpinusbelong，itwillbeobserved，tosoremoteanepochasthatofCopernicus。
　　ReferencehasbeenmadeinanearlierchaptertothemicroscopicinvestigationsofMarcelloMalpighi，who，asthererelated，wasthefirstobserverwhoactuallysawbloodcorpusclespassthroughthecapillaries。Anotherfeatofthisearliestofgreatmicroscopistswastodissectmusculartissue，andthusbecomethefatherofmicroscopicanatomy。ButMalpighididnotconfinehisobservationstoanimaltissues。Hedissectedplantsaswell，andheisalmostasfullyentitledtobecalledthefatherofvegetableanatomy，thoughherehishonorsaresharedbytheEnglishmanGrew。In1681，whileMalpighi’swork，Anatomiaplantarum，wasonitswaytotheRoyalSocietyforpublication，Grew’sAnatomyofVegetableswasinthehandsofthepublishers，makingitsappearanceafewmonthsearlierthantheworkofthegreatItalian。Grew’sbookwasepoch-markinginpointingoutthesex-differencesinplants。
　　RobertHookedevelopedthemicroscope，andtookthefirststepstowardsstudyingvegetableanatomy，publishingin1667，amongotherresults，thediscoveryofthecellularstructureofcork。
　　Hookeappliedthename"cell"forthefirsttimeinthisconnection。ThesediscoveriesofHooke，Malpighi，andGrew，andthediscoveryofthecirculationofthebloodbyWilliamHarveyshortlybefore，hadcalledattentiontothesimilarityofanimalandvegetablestructures。Halesmadeaseriesofinvestigationsuponanimalstodeterminetheforceofthebloodpressure；andsimilarlyhemadenumerousstaticalexperimentstodeterminethepressureoftheflowofsapinvegetables。HisVegetableStatics，publishedin1727，wasthefirstimportantworkonthesubjectofvegetablephysiology，andforthisreasonHaleshasbeencalledthefatherofthisbranchofscience。
　　Inbotany，aswellasinzoology，theclassificationsofLinnaeusofcoursesupplantedallprecedingclassifications，fortheobviousreasonthattheyweremuchmoresatisfactory；buthisworkwasaculminationofmanysimilarandmoreorlesssatisfactoryattemptsofhispredecessors。Abouttheyear1670
　　Dr。RobertMorison1620-1683，ofAberdeen，publishedaclassificationofplants，hissystemtakingintoaccountthewoodyorherbaceousstructure，aswellastheflowersandfruit。
　　ThisclassificationwassupplantedtwelveyearslaterbytheclassificationofRay，whoarrangedallknownvegetablesintothirty-threeclasses，thebasisofthisclassificationbeingthefruit。AfewyearslaterRivinus，aprofessorofbotanyintheUniversityofLeipzig，madestillanotherclassification，determiningthedistinguishingcharacterchieflyfromtheflower，andCamerariusandTournefortalsomadeelaborateclassifications。OntheContinentTournefort’sclassificationwasthemostpopularuntilthetimeofLinnaeus，hissystematicarrangementincludingabouteightthousandspeciesofplants，arrangedchieflyaccordingtotheformofthecorolla。
　　Mostoftheseearlyworkersgaveattentiontobothvegetableandanimalkingdoms。Theywerecallednaturalists，andthefieldoftheirinvestigationswasspokenofas"naturalhistory。"Thespecializationofknowledgehadnotreachedthatlaterstageinwhichbotanist，zoologist，andphysiologistfelttheirlaborstobesharplydivided。Suchadivisionwasbecomingmoreandmorenecessaryasthefieldofknowledgeextended；butitdidnotbecomeimperativeuntillongafterthetimeofLinnaeus。Thatnaturalisthimself，asweshallsee，wasequallydistinguishedasbotanistandaszoologist。Hisgreattaskoforganizingknowledgewasappliedtotheentirerangeoflivingthings。
　　CarolusLinnaeuswasborninthetownofRashult，inSweden，onMay13，1707。Asachildheshowedgreataptitudeinlearningbotanicalnames，andrememberingfactsaboutvariousplantsastoldhimbyhisfather。Hiseagernessforknowledgedidnotextendtotheordinaryprimarystudies，however，and，asidefromthesingleexceptionofthestudyofphysiology，heprovedhimselfanindifferentpupil。Hisbackwardnesswasasoretrialtohisfather，whowasdesirousthathissonshouldentertheministry；butastheyoungLinnaeusshowednolikingforthatcalling，andashehadacquittedhimselfwellinhisstudyofphysiology，hisfatheratlastdecidedtoallowhimtotakeupthestudyofmedicine。Hereatlastwasafieldmoretothelikingoftheboy，whosoonviedwiththebestofhisfellow-studentsforfirsthonors。Meanwhilehekeptsteadilyatworkinhisstudyofnaturalhistory，acquiringconsiderableknowledgeofornithology，entomology，andbotany，andaddingcontinuallytohiscollectionofbotanicalspecimens。In1729hisbotanicalknowledgewasbroughttotheattentionofOlafRudbeck，professorofbotanyintheUniversityofUpsala，byashortpaperonthesexesofplantswhichLinnaeushadprepared。Rudbeckwassoimpressedbysomeoftheideasexpressedinthispaperthatheappointedtheauthorashisassistantthefollowingyear。
　　ThiswasthebeginningofLinnaes’scareerasabotanist。Theacademicgardenswerethusthrownopentohim，andhefoundtimeathisdisposalforpursuinghisstudiesbetweenlecturehoursandintheevenings。ItwasatthistimethathebeganthepreparationofhisworktheSystemanaturae，thefirstofhisgreatworks，containingacomprehensivesketchofthewholefieldofnaturalhistory。Whenthisworkwaspublished，theclearnessoftheviewsexpressedandthesystematicarrangementofthevariousclassificationsexcitedgreatastonishmentandadmiration，andplacedLinaeusatonceintheforemostrankofnaturalists。Thisworkwasfollowedshortlybyotherpublications，mostlyonbotanicalsubjects，inwhich，amongotherthings，heworkedoutindetailhisfamous"system。"
　　Thissystemisfoundedonthesexesofplants，andisusuallyreferredtoasan"artificialmethod"ofclassificationbecauseittakesintoaccountonlyafewmarkedcharactersofplants，withoutunitingthembymoregeneralnaturalaffinities。Atthepresenttimeitisconsideredonlyasastepping-stonetothe"natural"system；butatthetimeofitspromulgationitwasepoch-markinginitsdirectnessandsimplicity，andthereforesuperiority，overanyexistingsystems。
　　OneofthegreatreformseffectedbyLinnaeuswasinthematterofscientificterminology。Technicaltermsareabsolutelynecessarytoscientificprogress，andparticularlysoinbotany，whereobscurity，ambiguity，orprolixityindescriptionsarefatallymisleading。Linnaeus’sworkcontainssomethinglikeathousandterms，whosemeaningsandusesarecarefullyexplained。
　　Suchanarrayseemsatfirstglancearbitraryandunnecessary，butthefactthatithasremainedinuseforsomethingliketwocenturiesisindisputableevidenceofitspracticality。Thedescriptivelanguageofbotany，asemployedbyLinnaeus，stillstandsasamodelforallothersubjects。
　　Closelyalliedtobotanicalterminologyisthesubjectofbotanicalnomenclature。TheoldmethodofusinganumberofLatinwordstodescribeeachdifferentplantisobviouslytoocumbersome，andseveralattemptshadbeenmadepriortothetimeofLinnaeustosubstitutesimplermethods。Linnaeushimselfmadeseveralunsatisfactoryattemptsbeforehefinallyhituponhissystemof"trivialnames，"whichwasdevelopedinhisSpeciesplantarum，andwhich，withsome，minoralterations，remainsinusetothisday。Theessenceofthesystemistheintroductionofbinomialnomenclature——thatistosay，theuseoftwonamesandnomoretodesignateanysinglespeciesofanimalorplant。Theprincipleisquitethesameasthataccordingtowhichinmodernsocietyamanhastwonames，letussay，JohnDoe，theonedesignatinghisfamily，theotherbeingindividual。Similarlyeachspeciesofanimalorplant，accordingtotheLinnaeeansystem，receivedaspecificor"trivial"name；whilevariousspecies，associatedaccordingtotheirseemingnaturalaffinitiesintogroupscalledgenera，weregiventhesamegenericname。ThusthegenericnamegivenallmembersofthecattribebeingFelis，thenameFelisleodesignatesthelion；Felispardus，theleopard；Felisdomestica，thehousecat，andsoon。Thisseemsperfectlysimpleandnaturalnow，buttounderstandhowgreatareformthebinomialnomenclatureintroducedwehavebuttoconsulttheworkofLinnaeus’spredecessors。Asingleillustrationwillsuffice。Thereis，forexample，akindofgrass，inreferringtowhichthenaturalistanteriortoLinnaeus，ifhewouldbeabsolutelyunambiguous，wasobligedtousethefollowingdescriptiveformula:GramenXerampelino，Miliacea，praetenuisramosaquesparsapanicula，siveXerampelinocongener，arvense，aestivum；gramenminutissimosemine。LinnaeusgavetothisplantthenamePoabulbosa——anamethatsufficed，accordingtothenewsystem，todistinguishthisfromeveryotherspeciesofvegetable。Itdoesnotrequireanyspecialknowledgetoappreciatetheadvantageofsuchasimplification。
　　WhilevisitingParisin1738Linnaeusmetandbotanizedwiththetwobotanistswhose"naturalmethod"ofclassificationwaslatertosupplanthisown"artificialsystem。"ThesewereBernardandAntoineLaurentdeJussieu。Theeffortsofthesetwoscientistsweredirectedtowardsobtainingasystemwhichshouldaimatclearness，simplicity，andprecision，andatthesametimebegovernedbythenaturalaffinitiesofplants。Thenaturalsystem，asfinallypropoundedbythem，isbasedonthenumberofcotyledons，thestructureoftheseed，andtheinsertionofthestamens。Succeedingwritersonbotanyhavemadevariousmodificationsofthissystem，butneverthelessitstandsasthefoundation-stoneofmodernbotanicalclassification。
　　TheworkofJohannesHevelius——HalleyandHevelius——Halley’sobservationofthetransitofMercury，andhismethodofdeterminingtheparallaxoftheplanets——Halley’sobservationofmeteors——Hisinabilitytoexplainthesebodies——TheimportantworkofJamesBradley——Lacaille’smeasurementofthearcofthemeridian——Thedeterminationofthequestionastotheexactshapeoftheearth——D’Alembertandhisinfluenceuponscience——
　　Delambre’sHistoryofAstronomy——TheastronomicalworkofEuler。
　　CHAPTERII。THEPROGRESSOFMODERNASTRONOMY
　　TheworkofWilliamHerschel——HisdiscoveryofUranus——Hisdiscoverythatthestarsaresuns——Hisconceptionoftheuniverse——Hisdeductionthatgravitationhascausedthegroupingoftheheavenlybodies——Thenebula，hypothesis，——ImmanuelKant’sconceptionoftheformationoftheworld——DefectsinKant’sconception——Laplace’sfinalsolutionoftheproblem——Hisexplanationindetail——ChangeinthementalattitudeoftheworldsinceBruno——Asteroidsandsatellites——DiscoveriesofOlbers1——ThemathematicalcalculationsofAdamsandLeverrier——ThediscoveryoftheinnerringofSaturn——ClerkMaxwell’spaperonthestabilityofSaturn’srings——Helmholtz’sconceptionoftheactionoftidalfriction——ProfessorG。H。Darwin’sestimateoftheconsequencesoftidalaction——Cometsandmeteors——Bredichin’scometarytheory——Thefinalsolutionofthestructureofcomets——Newcomb’sestimateoftheamountofcometarydustsweptupdailybytheearth——Thefixedstars——JohnHerschel’sstudiesofdoublestars——Fraunhofer’sperfectionoftherefractingtelescope——Bessel’smeasurementoftheparallaxofastar，——Henderson’smeasurements——KirchhoffandBunsen’sperfectionofthespectroscope——Wonderfulrevelationsofthespectroscope——LordKelvin’sestimateofthetimethatwillberequiredfortheearthtobecomecompletelycooled——
　　AlvanClark’sdiscoveryofthecompanionstarofSirius——
　　Theadventofthephotographicfilminastronomy——Dr。
　　Huggins’sstudiesofnebulae——SirNormanLockyer’s"cosmogonicguess，"——Croll’spre-nebulartheory。
　　CHAPTERIII。THENEWSCIENCEOFPALEONTOLOGY
　　WilliamSmithandfossilshells——Hisdiscoverythatfossilrocksarearrangedinregularsystems——Smith’sinquiriestakenupbyCuvier——HisOssementsFossilescontainingthefirstdescriptionofhairyelephant——Hiscontentionthatfossilsrepresentextinctspeciesonly——Dr。Buckland’sstudiesofEnglishfossil-beds——CharlesLyellcombatscatastrophism，——Elaborationofhisideaswithreferencetotherotationofspecies——Theestablishmentofthedoctrineofuniformitarianism，——Darwin’sOriginofSpecies——Fossilman——Dr。Falconer’svisittothefossil-bedsinthevalleyoftheSomme——InvestigationsofPrestwichandSirJohnEvans——DiscoveryoftheNeanderthalskull，——Cuvier’srejectionofhumanfossils——Thefindingofprehistoriccarvingonivory——Thefossil-bedsofAmerica——ProfessorMarsh’spaperonthefossilhorsesinAmerica——TheWarrenmastodon，——TheJavafossil，PithecanthropusErectus。
　　CHAPTERIV。THEORIGINANDDEVELOPMENTOFMODERNGEOLOGY
　　JamesHuttonandthestudyoftherocks——Histheoryoftheearth——Hisbeliefinvolcaniccataclysmsinraisingandformingthecontinents——HisfamouspaperbeforetheRoyalSocietyofEdinburgh，1781——Hisconclusionsthatallstrataoftheearthhavetheiroriginatthebottomofthesea——Hisdeductionthatheatedandexpandedmattercausedtheelevationoflandabovethesea-level——Indifferenceatfirstshownthisremarkablepaper——NeptunistsversusPlutonists——
　　Scrope’sclassicalworkonvolcanoes——FinalacceptanceofHutton’sexplanationoftheoriginofgranites——Lyellanduniformitarianism——Observationsonthegradualelevationofthecoast-linesofSwedenandPatagonia——Observationsontheenormousamountoflanderosionconstantlytakingplace，——Agassizandtheglacialtheory——Perraudinthechamois-
　　hunter，andhisexplanationofperchedbowlders——DeCharpentier’sacceptanceofPerraudin’sexplanation——Agassiz’spaperonhisAlpinestudies——HisconclusionthattheAlpswereoncecoveredwithanice-sheet——Finalacceptanceoftheglacialtheory——Thegeologicalages——TheworkofMurchisonandSedgwick——FormationoftheAmericancontinents——Past，present，andfuture。
　　CHAPTERV。THENEWSCIENCEOFMETEOROLOGY
　　Biot’sinvestigationsofmeteors——TheobservationsofBrandesandBenzenbergonthevelocityoffallingstars——
　　ProfessorOlmstead’sobservationsonthemeteoricshowerof1833——
　　ConfirmationofChladni’shypothesisof1794——Theauroraborealis——Franklin’ssuggestionthatitisofelectricalorigin——Itscloseassociationwithterrestrialmagnetism——Evaporation，cloud-formation，anddew——Dalton’sdemonstrationthatwaterexistsintheairasanindependentgas——Hutton’stheoryofrain——LukeHoward’spaperonclouds——Observationsondew，byProfessorWilsonandMr。Six——Dr。Wells’sessayondew——Hisobservationsonseveralappearancesconnectedwithdew——Isothermsandoceancurrents——Humboldtandthe-scienceofcomparativeclimatology——Hisstudiesofoceancurrents——
　　Maury’stheorythatgravityisthecauseofoceancurrents——
　　Dr。CrollonClimateandTime——Cyclonesandanti-cyclones，——Dove’sstudiesinclimatology——ProfessorFerrel’smathematicallawofthedeflectionofwinds——Tyndall’sestimateoftheamountofheatgivenoffbytheliberationofapoundofvapor——Meteorologicalobservationsandweatherpredictions。
　　CHAPTERVI。MODERNTHEORIESOFHEATANDLIGHT
　　JosiahWedgwoodandtheclaypyrometer——CountRumfordandthevibratorytheoryofheat——Hisexperimentswithboringcannontodeterminethenatureofheat——Causingwatertoboilbythefrictionoftheborer——Hisfinaldeterminationthatheatisaformofmotion——ThomasYoungandthewavetheoryoflight——Hispaperonthetheoryoflightandcolors——Hisexpositionofthecolorsofthinplates——Ofthecolorsofthickplates，andofstriatedsurfaces，——AragoandFresnelchampionthewavetheory——oppositiontothetheorybyBiot——TheFrenchAcademy’stacitacceptanceofthecorrectnessofthetheorybyitsadmissionofFresnelasamember。
　　CHAPTERVII。THEMODERNDEVELOPMENTOFELECTRICITYANDMAGNETISM
　　Galvaniandthebeginningofmodernelectricity——Theconstructionofthevoltaicpile——Nicholson’sandCarlisle’sdiscoverythatthegalvaniccurrentdecomposeswater——DecompositionofvarioussubstancesbySirHumphryDavy——Hisconstructionofanarc-light——ThedeflectionofthemagneticneedlebyelectricitydemonstratedbyOersted——Effectofthisimportantdiscovery——Amperecreatesthescienceofelectro-dynamics——JosephHenry’sstudiesofelectromagnets——MichaelFaradaybeginshisstudiesofelectromagneticinduction——HisfamouspaperbeforetheRoyalSociety，in1831，inwhichhedemonstrateselectro-magneticinduction——HisexplanationofArago’srotatingdisk——Thesearchforasatisfactorymethodofstoringelectricity——
　　Roentgenrays，orX-rays。
　　CHAPTERVIII。THECONSERVATIONOFENERGY
　　Faradaynarrowlymissesthediscoveryofthedoctrineofconservation——Carnot’sbeliefthatadefinitequantityofworkcanbetransformedintoadefinitequantityofheat——TheworkofJamesPrescottJoule——InvestigationsbegunbyDr。
　　Mayer——Mayer’spaperof1842——Hisstatementofthelawoftheconservationofenergy——MayerandHelmholtz——Joule’spaperof1843——JouleorMayer——LordKelvinandthedissipationofenergy-Thefinalunification。
　　CHAPTERIX。THEETHERANDPONDERABLEMATTER
　　JamesClerk-Maxwell’sconceptionofether——ThomasYoungand"Luminiferousether，"——Young’sandFresnel’sconceptionoftransverseluminiferousundulations——Faraday’sexperimentspointingtotheexistenceofether——ProfessorLodge’ssuggestionoftwoethers——LordKelvin’scalculationoftheprobabledensityofether——Thevortextheoryofatoms——Helmholtz’scalculationsinvortexmotions——ProfessorTait’sapparatusforcreatingvortexringsintheair——TheultimateconstitutionofmatterasconceivedbyBoscovich——Davy’sspeculationsastothechangesthatoccurinthesubstanceofmatteratdifferenttemperatures——Clausius’sandMaxwell’sinvestigationsofthekinetictheoryofgases——LordKelvin’sestimateofthesizeofthemolecule——
　　Studiesofthepotentialenergyofmolecules——Actionofgasesatlowtemperatures。
　　APPENDIX
　　AHISTORYOFSCIENCE
　　BOOKIII
　　MODERNDEVELOPMENTOFTHEPHYSICAL
　　SCIENCES
　　Withthepresentbookweenterthefieldofthedistinctivelymodern。Thereisnoprecisedateatwhichwetakeupeachofthesuccessivestories，butthemainsweepofdevelopmenthastodoineachcasewiththenineteenthcentury。Weshallseeatoncethatthisisatimebothofrapidprogressandofgreatdifferentiation。Wehaveheardalmostnothinghithertoofsuchsciencesaspaleontology，geology，andmeteorology，eachofwhichnowdemandsfullattention。
　　Meantime，astronomyandwhattheworkersoftheelderdaycallednaturalphilosophybecomewonderfullydiversifiedandpresentnumerousphasesthatwouldhavebeenstartlingenoughtothestar-gazersandphilosophersoftheearlierepoch。
　　Thus，forexample，inthefieldofastronomy，Herschelisable，thankstohisperfectedtelescope，todiscoveranewplanetandthentoreachoutintothedepthsofspaceandgainsuchknowledgeofstarsandnebulaeashithertonoonehadmorethandreamedof。
　　Then，inrapidsequence，awholecoterieofhithertounsuspectedminorplanetsisdiscovered，stellardistancesaremeasured，somemembersofthestarrygalaxyaretimedintheirflight，thedirectionofmovementofthesolarsystemitselfisinvestigated，thespectroscoperevealsthechemicalcompositionevenofsunsthatareunthinkablydistant，andatangibletheoryisgraspedoftheuniversalcyclewhichincludesthebirthanddeathofworlds。
　　Similarlythenewstudiesoftheearth’ssurfacerevealsecretsofplanetaryformationhithertoquiteinscrutable。
　　Itbecomesknownthatthestrataoftheearth’ssurfacehavebeenformingthroughoutuntoldages，andthatsuccessivepopulationsdifferingutterlyfromoneanotherhavepeopledtheearthindifferentgeologicalepochs。Theentirepointofviewofthoughtfulmenbecomeschangedincontemplatingthehistoryoftheworldinwhichwelive——albeitthenewestthoughtharksbacktosomeextenttothosedayswhentheinspiredthinkersofearlyGreecedreamedoutthewonderfultheorieswithwhichourearlierchaptershavemadeourreadersfamiliar。
　　Intheregionofnaturalphilosophyprogressisnolesspronouncedandnolessstriking。Itsufficeshere，however，bywayofanticipation，simplytonamethegreatestgeneralizationofthecenturyinphysicalscience——thedoctrineoftheconservationofenergy。
　　I
　　THESUCCESSORSOFNEWTONINASTRONOMY
　　HEVELIUSANDHALLEY
　　STRANGELYenough，thedecadeimmediatelyfollowingNewtonwasoneofcomparativebarrennessinscientificprogress，theearlyyearsoftheeighteenthcenturynotbeingasproductiveofgreatastronomersasthelateryearsoftheseventeenth，or，forthatmatter，asthelateryearsoftheeighteenthcenturyitself。Severaloftheprominentastronomersofthelaterseventeenthcenturylivedonintotheopeningyearsofthefollowingcentury，however，andtheyoungergenerationsoondevelopedacoterieofastronomers，amongwhomEuler，Lagrange，Laplace，andHerschel，asweshallsee，weretoaccomplishgreatthingsinthisfieldbeforethecenturyclosed。
　　Oneofthegreatseventeenth-centuryastronomers，whodiedjustbeforethecloseofthecentury，wasJohannesHevelius1611-1687，ofDantzig，whoadvancedastronomybyhisaccuratedescriptionofthefaceandthespotsofthemoon。Butheisrememberedalsoforhavingretardedprogressbyhisinfluenceinrefusingtousetelescopicsightsinhisobservations，preferringuntilhisdeaththeplainsightslongbeforediscardedbymostotherastronomers。TheadvantagesofthesetelescopesightshavebeendiscussedunderthearticletreatingofRobertHooke，butnosuchadvantageswereeverrecognizedbyHevelius。
　　SogreatwasHevelius’sreputationasanastronomerthathisrefusaltorecognizetheadvantageofthetelescopesightscausedmanyastronomerstohesitatebeforeacceptingthemassuperiortotheplain；andeventhefamousHalley，ofwhomweshallspeakfurtherinamoment，wassufficientlyindoubtoverthemattertopaytheagedastronomeravisittotesthisskillinusingtheold-stylesights。Sidebyside，HeveliusandHalleymadetheirobservations，HeveliuswithhisoldinstrumentandHalleywiththenew。Theresultsshowedslightlyintheyoungerman’sfavor，butnotenoughtomakeitanentirelyconvincingdemonstration。
　　Theexplanationofthis，however，didnotlieinthelackofsuperiorityofthetelescopicinstrument，butratherinthemarvellousskilloftheagedHevelius，whosedexterityalmostcompensatedforthedefectofhisinstrument。Whathemighthaveaccomplishedcouldhehavebeeninducedtoadoptthetelescopecanonlybesurmised。
　　Halleyhimselfwasbynomeansatyroinmattersastronomicalatthattime。Astheonlysonofawealthysoap-boilerlivingnearLondon，hehadbeengivenaliberaleducation，andevenbeforeleavingcollegemadesuchnovelscientificobservationsasthatofthechangeinthevariationofthecompass。Atnineteenyearsofagehediscoveredanewmethodofdeterminingtheelementsoftheplanetaryorbitswhichwasadistinctimprovementovertheold。TheyearfollowinghesailedfortheIslandofSt，Helenatomakeobservationsoftheheavensinthesouthernhemisphere。
　　ItwaswhileinSt。HelenathatHalleymadehisfamousobservationofthetransitofMercuryoverthesun’sdisk，thisobservationbeingconnected，indirectlyatleast，withhisdiscoveryofamethodofdeterminingtheparallaxoftheplanets。Byparallaxismeanttheapparentchangeinthepositionofanobject，duereallytoachangeinthepositionoftheobserver。
　　Thus，ifweimaginetwoastronomersmakingobservationsofthesunfromoppositesidesoftheearthatthesametime，itisobviousthattotheseobserversthesunwillappeartobeattwodifferentpointsinthesky。Halftheanglemeasuringthisdifferencewouldbeknownasthesun’sparallax。Thiswoulddepend，then，uponthedistanceoftheearthfromthesunandthelengthoftheearth’sradius。
　　Sincetheactuallengthofthisradiushasbeendetermined，theparallaxofanyheavenlybodyenablestheastronomertodetermineitsexactdistance。
　　Theparallaxescanbedeterminedequallywell，however，iftwoobserversareseparatedbyexactlyknowndistances，severalhundredsorthousandsofmilesapart。
　　InthecaseofatransitofVenusacrossthesun’sdisk，forexample，anobserveratNewYorknotestheimageoftheplanetmovingacrossthesun’sdisk，andnotesalsotheexacttimeofthisobservation。InthesamemanneranobserveratLondonmakessimilarobservations。
　　KnowingthedistancebetweenNewYorkandLondon，andthedifferenttimeofthepassage，itisthuspossibletocalculatethedifferenceoftheparallaxesofthesunandaplanetcrossingitsdisk。Theideaofthusdeterminingtheparallaxoftheplanetsoriginated，oratleastwasdeveloped，byHalley，andfromthisphenomenonhethoughtitpossibletoconcludethedimensionsofalltheplanetaryorbits。Asweshallseefurtheron，hisviewswerefoundtobecorrectbylaterastronomers。
　　In1721HalleysucceededFlamsteedasastronomerroyalattheGreenwichObservatory。Althoughsixty-
　　fouryearsofageatthattimehisactivityinastronomycontinuedunabatedforanotherscoreofyears。AtGreenwichheundertooksometediousobservationsofthemoon，andduringthoseobservationswasfirsttodetecttheaccelerationofmeanmotion。Hewasunabletoexplainthis，however，anditremainedforLaplaceintheclosingyearsofthecenturytodoso，asweshallseelater。
　　Halley’sbook，theSynopsisAstronomiaeCometicae，isoneofthemostvaluableadditionstoastronomicalliteraturesincethetimeofKepler。Hewasfirsttoattemptthecalculationoftheorbitofacomet，havingrevivedtheancientopinionthatcometsbelongtothesolarsystem，movingineccentricorbitsroundthesun，andhiscalculationoftheorbitofthecometof1682ledhimtopredictcorrectlythereturnofthatcometin1758。Halley’sStudyofMeteors。
　　Likeotherastronomersofhistimebewasgreatlypuzzledoverthewell-knownphenomenaofshooting-
　　stars，ormeteors，makingmanyobservationshimself，andexaminingcarefullytheobservationsofotherastronomers。In1714hegavehisviewsastotheoriginandcompositionofthesemysteriousvisitorsintheearth’satmosphere。Asthissubjectwillbeagainreferredtoinalaterchapter，Halley’sviews，representingthemostadvancedviewsofhisage，areofinterest。
　　"Thetheoryoftheairseemethatpresent，"hesays，"tobeperfectlywellunderstood，andthedifferingdensitiesthereofatallaltitudes；forsupposingthesameairtooccupyspacesreciprocallyproportionaltothequantityofthesuperiororincumbentair，Ihaveelsewhereprovedthatatfortymileshightheairisrarerthanatthesurfaceoftheearthatthreethousandtimes；andthattheutmostheightoftheatmosphere，whichreflectslightintheCrepusculum，isnotfullyforty-fivemiles，notwithstandingwhich’tisstillmanifestthatsomesortofvapors，andthoseinnosmallquantity，arisenearlytothatheight。AninstanceofthismaybegiveninthegreatlightthesocietyhadanaccountofvideTransact。Sep。，1676
　　fromDr。Wallis，whichwasseeninverydistantcountiesalmostoverallthesouthpartofEngland。Ofwhichthoughthedoctorcouldnotgetsoparticulararelationaswasrequisitetodeterminetheheightthereof，yetfromthedistantplacesitwasseenin，itcouldnotbutbeverymanymileshigh。
　　"Solikewisethatmeteorwhichwasseenin1708，onthe31stofJuly，betweennineandteno’clockatnight，wasevidentlybetweenfortyandfiftymilesperpendicularlyhigh，andasnearasIcangather，overSherenessandthebuoyontheNore。ForitwasseenatLondonmovinghorizontallyfromeastbynorthtoeastbysouthatleastfiftydegreeshigh，andatRedgrove，inSuffolk，ontheYarmouthroad，abouttwentymilesfromtheeastcoastofEngland，andatleastfortymilestotheeastwardofLondon，itappearedalittletothewestwardofthesouth，supposesouthbywest，andwasseenaboutthirtydegreeshigh，slidingobliquelydownward。Iwasshowninbothplacesthesituationthereof，whichwasasdescribed，butcouldwishsomepersonskilledinastronomicalmattersbadseenit，thatwemightpronounceconcerningitsheightwithmorecertainty。Yet，asitis，wemaysecurelyconcludethatitwasnotmanymoremileswesterlythanRedgrove，which，asIsaidbefore，isaboutfortymilesmoreeasterlythanLondon。Supposeit，therefore，whereperpendicular，tohavebeenthirty-fivemileseastfromLondon，andbythealtitudeitappearedatinLondon——
　　viz。，fiftydegrees，itstangentwillbeforty-twomiles，fortheheightofthemeteorabovethesurfaceoftheearth；whichalsoisratheroftheleast，becausethealtitudeoftheplaceshownmeisrathermorethanlessthanfiftydegrees；andthelikemaybeconcludedfromthealtitudeitappearedinatRedgrove，nearseventymilesdistant。Thoughatthisverygreatdistance，itappearedtomovewithanincrediblevelocity，darting，inaveryfewsecondsoftime，forabouttwelvedegreesofagreatcirclefromnorthtosouth，beingverybrightatitsfirstappearance；anditdiedawayattheeastofitscourse，leavingforsometimeapalewhitenessintheplace，withsomeremainsofitinthetrackwhereithadgone；butnohissingsoundasitpassed，orbounceofanexplosionwereheard。
　　"Itmaydeservethehonorablesociety’sthoughts，howsogreataquantityofvaporshouldberaisedtothetopoftheatmosphere，andtherecollected，soasuponitsascensionorotherwiseillumination，togivealighttoacircleofaboveonehundredmilesdiameter，notmuchinferiortothelightofthemoon；
　　soasonemightseetotakeapinfromthegroundintheotherwisedarknight。’Tishardtoconceivewhatsortofexhalationsshouldrisefromtheearth，eitherbytheactionofthesunorsubterraneanheat，soastosurmounttheextremecoldandrarenessoftheairinthoseupperregions:butthefactisindisputable，andthereforerequiresasolution。"
　　Fromthismuchofthepaperitappearsthattherewasageneralbeliefthatthisburningmasswasheatedvaporthrownofffromtheearthinsomemysteriousmanner，yetthisisunsatisfactorytoHalley，foraftercitingvariousothermeteorsthathaveappearedwithinhisknowledge，hegoesontosay:
　　"Whatsortofsubstanceitmustbe，thatcouldbesoimpelledandignitedatthesametime；therebeingnoVulcanoorotherSpiraculumofsubterraneousfireinthenortheastpartsoftheworld，thatweeveryetheardof，fromwhenceitmightbeprojected。
　　"Ihavemuchconsideredthisappearance，andthinkitoneofthehardestthingstoaccountforthatIhaveyetmetwithinthephenomenaofmeteors，andIaminducedtothinkthatitmustbesomecollectionofmatterformedintheaether，asitwere，bysomefortuitousconcourseofatoms，andthattheearthmetwithitasitpassedalonginitsorb，thenbutnewlyformed，andbeforeithadconceivedanygreatimpetusofdescenttowardsthesun。Forthedirectionofitwasexactlyoppositetothatoftheearth，whichmadeananglewiththemeridianatthattimeofsixty-sevengr。，thatis，itscoursewasfromwestsouthwesttoeastnortheast，whereforethemeteorseemedtomovethecontraryway。Andbesidesfallingintothepoweroftheearth’sgravity，andlosingitsmotionfromtheoppositionofthemedium，itseemsthatitdescendedtowardstheearth，andwasextinguishedintheTyrrheneSea，tothewestsouthwestofLeghorn。Thegreatblowbeinghearduponitsfirstimmersionintothewater，andtherattlinglikethedrivingofacartoverstonesbeingwhatsucceededuponitsquenching；
　　somethinglikethisisalwayshearduponquenchingaveryhotironinwater。Thesefactsbeingpastdispute，Iwouldbegladtohavetheopinionofthelearnedthereon，andwhatobjectioncanbereasonablymadeagainsttheabovehypothesis，whichIhumblysubmittotheircensure。"[1]
　　Thesefewparagraphs，comingastheydofromaleadingeighteenth-centuryastronomer，conveymoreclearlythananycommenttheactualstateofthemeteorologicallearningatthattime。Thatthisballoffire，rushing"atagreatervelocitythantheswiftestcannon-ball，"wassimplyamassofheatedrockpassingthroughouratmosphere，didnotoccurtohim，oratleastwasnotcredited。Noristhissurprisingwhenwereflectthatatthattimeuniversalgravitationhadbeenbutrecentlydiscovered；heathadnotasyetbeenrecognizedassimplyaformofmotion；andthunderandlightningwereunexplainedmysteries，nottobeexplainedforanotherthree-quartersofacentury。
　　InthechapteronmeteorologyweshallseehowthesolutionofthismysterythatpuzzledHalleyandhisassociatesalltheirliveswasfinallyattained。
　　BRADLEYANDTHEABERRATIONOFLIGHT
　　HalleywassucceededasastronomerroyalbyamanwhoseusefuladditionstothesciencewerenottoberecognizedorappreciatedfullyuntilbroughttolightbythePrussianastronomerBesselearlyinthenineteenthcentury。ThiswasDr。JamesBradley，anecclesiastic，whoranksasoneofthemosteminentastronomersoftheeighteenthcentury。Hismostremarkablediscoverywastheexplanationofapeculiarmotionofthepole-star，firstobserved，butnotexplained，byPicardacenturybefore。FormanyyearsasatisfactoryexplanationwassoughtunsuccessfullybyBradleyandhisfellow-astronomers，butatlasthewasabletodemonstratethatthestaryDraconis，onwhichhewasmakinghisobservations，described，orappearedtodescribe，asmallellipse。Ifthisobservationwascorrect，itaffordedameansofcomputingtheaberrationofanystaratalltimes。Theexplanationofthephysicalcauseofthisaberration，asBradleythought，andafterwardsdemonstrated，wastheresultofthecombinationofthemotionoflightwiththeannualmotionoftheearth。Bradleyfirstformulatedthistheoryin1728，butitwasnotuntil1748——twentyyearsofcontinuousstruggleandobservationbyhim——thathewaspreparedtocommunicatetheresultsofhiseffortstotheRoyalSociety。ThisremarkablepaperisthoughtbytheFrenchman，Delambre，toentitleitsauthortoaplaceinsciencebesidesuchastronomersasHipparcbusandKepler。
　　Bradley’sstudiesledhimtodiscoveralsothelibratorymotionoftheearth’saxis。"AsthisappearanceofgDraconis。indicatedadiminutionoftheinclinationoftheearth’saxistotheplaneoftheecliptic，"hesays；"andasseveralastronomershavesupposedTHATinclinationtodiminishregularly；ifthisphenomenondependeduponsuchacause，andamountedto18"innineyears，theobliquityoftheeclipticwould，atthatrate，alterawholeminuteinthirtyyears；whichismuchfasterthananyobservations，beforemade，wouldallow。Ihadreason，therefore，tothinkthatsomepartofthismotionattheleast，ifnotthewhole，wasowingtothemoon’sactionupontheequatorialpartsoftheearth；which，Iconceived，mightcausealibratorymotionoftheearth’saxis。ButasI
　　wasunabletojudge，fromonlynineyearsobservations，whethertheaxiswouldentirelyrecoverthesamepositionthatithadintheyear1727，Ifounditnecessarytocontinuemyobservationsthroughawholeperiodofthemoon’snodes；attheendofwhichIhadthesatisfactiontosee，thatthestars，returnedintothesamepositionagain；asiftherehadbeennoalterationatallintheinclinationoftheearth’saxis；whichfullyconvincedmethatIhadguessedrightlyastothecauseofthephenomena。Thiscircumstanceproveslikewise，thatiftherebeagradualdiminutionoftheobliquityoftheecliptic，itdoesnotariseonlyfromanalterationinthepositionoftheearth’saxis，butratherfromsomechangeintheplaneoftheeclipticitself；becausethestars，attheendoftheperiodofthemoon’snodes，appearedinthesameplaces，withrespecttotheequator，astheyoughttohavedone，iftheearth’saxishadretainedthesameinclinationtoaninvariableplane。"[2]