Itappears，then，thatthemechanicalstudiesofGalileo，takenasawhole，werenothinglessthanrevolutionary。TheyconstitutedthefirstgreatadvanceuponthedynamicstudiesofArchimedes，andthenledtothesecurefoundationforoneofthemostimportantofmodernsciences。WeshallseethatanimportantcompanyofstudentsenteredthefieldimmediatelyafterthetimeofGalileo，andcarriedforwardtheworkhehadsowellbegun。
　　Butbeforepassingontotheconsiderationoftheirlabors，wemustconsiderworkinalliedfieldsoftwomenwhowerecontemporariesofGalileoandwhoseoriginallaborswereinsomerespectsscarcelylessimportantthanhisown。ThesemenaretheDutchmanStevinus，whomustalwaysberememberedasaco-laborerwithGalileointhefoundationofthescienceofdynamics，andtheEnglishmanGilbert，towhomisduetheunqualifiedpraiseoffirstsubjectingthephenomenonofmagnetismtoastrictlyscientificinvestigation。
　　Stevinuswasbornintheyear1548，anddiedin1620。Hewasamanofapracticalgenius，andheattractedtheattentionofhisnon-scientificcontemporaries，amongotherways，bytheconstructionofacuriousland-craft，which，mountedonwheels，wastobepropelledbysailslikeaboat。Notonlydidhewriteabookonthiscurioushorselesscarriage，butheputhisideaintopracticalapplication，producingavehiclewhichactuallytraversedthedistancebetweenScheveningenandPetton，withnofewerthantwenty-sevenpassengers，oneofthembeingPrinceMauriceofOrange。Thisdemonstrationwasmadeabouttheyear1600。Itdoesnotappear，however，thatanyimportantusewasmadeofthestrangevehicle；butthemanwhoinventeditputhismechanicalingenuitytootherusewithbettereffect。Itwashewhosolvedtheproblemofobliqueforces，andwhodiscoveredtheimportanthydrostaticprinciplethatthepressureoffluidsisproportionatetotheirdepth，withoutregardtotheshapeoftheincludingvessel。
　　ThestudyofobliqueforceswasmadebyStevinuswiththeaidofinclinedplanes。Hismostdemonstrativeexperimentwasaverysimpleone，inwhichachainofballsofequalweightwashungfromatriangle；thetrianglebeingsoconstructedastorestonahorizontalbase，theobliquesidesbearingtherelationtoeachotheroftwotoone。Stevinusfoundthathischainofballsjustbalancedwhenfourballswereonthelongersideandtwoontheshorterandsteeperside。Thebalancingofforcethusbroughtaboutconstitutedastableequilibrium，Stevinusbeingthefirsttodiscriminatebetweensuchaconditionandtheunbalancedconditioncalledunstableequilibrium。Bythissimpleexperimentwaslaidthefoundationofthescienceofstatics。Stevinushadafullgraspoftheprinciplewhichhisexperimentinvolved，andheappliedittothesolutionofobliqueforcesinalldirections。
　　EarlierinvestigationsofStevinuswerepublishedin1608。HiscollectedworkswerepublishedatLeydenin1634。
　　ThisstudyoftheequilibriumofpressureofbodiesatrestledStevinus，notunnaturally，toconsiderthealliedsubjectofthepressureofliquids。Heistobecreditedwiththeexplanationoftheso-calledhydrostaticparadox。Thefamiliarmodernexperimentwhichillustratesthisparadoxismadebyinsertingalongperpendiculartubeofsmallcaliberintothetopofatightbarrel。Onfillingthebarrelandtubewithwater，itispossibletoproduceapressurewhichwillburstthebarrel，thoughitbeastrongone，andthoughtheactualweightofwaterinthetubeiscomparativelyinsignificant。Thisillustratesthefactthatthepressureatthebottomofacolumnofliquidisproportionatetotheheightofthecolumn，andnottoitsbulk，thisbeingthehydrostaticparadoxinquestion。Theexplanationisthatanenclosedfluidunderpressureexertsanequalforceuponallpartsofthecircumscribingwall；theaggregatepressuremay，therefore，beincreasedindefinitelybyincreasingthesurface。
　　Itisthisprinciple，ofcourse，whichisutilizedinthefamiliarhydrostaticpress。Theoreticalexplanationsofthepressureofliquidsweresuppliedagenerationortwolaterbynumerousinvestigators，includingNewton，butthepracticalrefoundationofthescienceofhydrostaticsinmoderntimesdatesfromtheexperimentsofStevinus。
　　GALILEOANDTHEEQUILIBRIUMOFFLUIDS
　　Experimentsofanalliedcharacter，havingtodowiththeequilibriumoffluids，exercisedtheingenuityofGalileo。Someofhismostinterestingexperimentshavetodowiththesubjectoffloatingbodies。ItwillberecalledthatArchimedes，awaybackintheAlexandrianepoch，hadsolvedthemostimportantproblemsofhydrostaticequilibrium。Now，however，hisexperimentswereoverlookedorforgotten，andGalileowasobligedtomakeexperimentsanew，andtocombatfallaciousviewsthatoughtlongsincetohavebeenabandoned。PerhapsthemostilluminativeviewofthespiritofthetimescanbegainedbyquotingatlengthapaperofGalileo’s，inwhichhedetailshisownexperimentswithfloatingbodiesandcontrovertstheviewsofhisopponents。ThepaperhasfurthervalueasillustratingGalileo’smethodsbothasexperimenterandasspeculativereasoner。
　　Thecurrentview，whichGalileohereundertakestorefute，assertsthatwateroffersresistancetopenetration，andthatthisresistanceisinstrumentalindeterminingwhetherabodyplacedinwaterwillfloatorsink。Galileocontendsthatwaterisnon-resistant，andthatbodiesfloatorsinkinvirtueoftheirrespectiveweights。This，ofcourse，ismerelyarestatementofthelawofArchimedes。Butitremainstoexplainthefactthatbodiesofacertainshapewillfloat，whilebodiesofthesamematerialandweight，butofadifferentshape，willsink。WeshallseewhatexplanationGalileofindsofthisanomalyasweproceed。
　　Inthefirstplace，Galileomakesaconeofwoodorofwax，andshowsthatwhenitfloatswitheitheritspointoritsbaseinthewater，itdisplacesexactlythesameamountoffluid，althoughtheapexisbyitsshapebetteradaptedtoovercometheresistanceofthewater，ifthatwerethecauseofbuoyancy。
　　Again，theexperimentmaybevariedbytemperingthewaxwithfilingsofleadtillitsinksinthewater，whenitwillbefoundthatinanyfigurethesamequantityofcorkmustbeaddedtoittoraisethesurface。
　　"But，"saysGalileo，"thissilencesnotmyantagonists；theysaythatallthediscoursehithertomadebymeimportslittletothem，andthatitservestheirturn；thattheyhavedemonstratedinoneinstance，andinsuchmannerandfigureaspleasesthembest——namely，inaboardandinaballofebony——thatonewhenputintothewatersinkstothebottom，andthattheotherstaystoswimonthetop；andthematterbeingthesame，andthetwobodiesdifferinginnothingbutinfigure，theyaffirmthatwithallperspicuitytheyhavedemonstratedandsensiblymanifestedwhattheyundertook。Nevertheless，Ibelieve，andthinkIcanprove，thatthisveryexperimentprovesnothingagainstmytheory。Andfirst，itisfalsethattheballsinksandtheboardnot；fortheboardwillsink，too，ifyoudotoboththefiguresasthewordsofourquestionrequire；thatis，ifyouputthembothinthewater；fortobeinthewaterimpliestobeplacedinthewater，andbyAristotle’sowndefinitionofplace，tobeplacedimportstobeenvironedbythesurfaceoftheambientbody；butwhenmyantagonistsshowthefloatingboardofebony，theyputitnotintothewater，butuponthewater；where，beingdetainedbyacertainimpedimentofwhichmoreanon，itissurrounded，partlywithwater，partlywithair，whichiscontrarytoouragreement，forthatwasthatbodiesshouldbeinthewater，andnotpartinthewater，partintheair。
　　"Iwillnotomitanotherreason，foundedalsouponexperience，and，ifIdeceivenotmyself，conclusiveagainstthenotionthatfigure，andtheresistanceofthewatertopenetration，haveanythingtodowiththebuoyancyofbodies。Chooseapieceofwoodorothermatter，as，forinstance，walnut-wood，ofwhichaballrisesfromthebottomofthewatertothesurfacemoreslowlythanaballofebonyofthesamesizesinks，sothat，clearly，theballofebonydividesthewatermorereadilyinsinkingthantheballofwooddoesinrising。Thentakeaboardofwalnut-treeequaltoandlikethefloatingoneofmyantagonists；andifitbetruethatthislatterfloatsbyreasonofthefigurebeingunabletopenetratethewater，theotherofwalnut-tree，withoutaquestion，ifthrusttothebottom，oughttostaythere，ashavingthesameimpedingfigure，andbeinglessapttoovercomethesaidresistanceofthewater。Butifwefindbyexperiencethatnotonlythethinboard，buteveryotherfigureofthesamewalnut-tree，willreturntofloat，asunquestionablyweshall，thenImustdesiremyopponentstoforbeartoattributethefloatingoftheebonytothefigureoftheboard，sincetheresistanceofthewateristhesameinrisingasinsinking，andtheforceofascensionofthewalnut-treeislessthantheebony’sforceforgoingtothebottom。
　　"Nowletusreturntothethinplateofgoldorsilver，orthethinboardofebony，andletuslayitlightlyuponthewater，sothatitmaystaytherewithoutsinking，andcarefullyobservetheeffect。Itwillappearclearlythattheplatesareaconsiderablematterlowerthanthesurfaceofthewater，whichrisesupandmakesakindoframpartroundthemoneveryside。Butifithasalreadypenetratedandovercomethecontinuityofthewater，andisofitsownnatureheavierthanthewater，whydoesitnotcontinuetosink，butstopandsuspenditselfinthatlittledimplethatitsweighthasmadeinthewater？Myansweris，becauseinsinkingtillitssurfaceisbelowthewater，whichrisesupinabankroundit，itdrawsafterandcarriesalongwithittheairaboveit，sothatthatwhich，inthiscase，descendsinthewaterisnotonlytheboardofebonyortheplateofiron，butacompoundofebonyandair，fromwhichcompositionresultsasolidnolongerspecificallyheavierthanthewater，aswastheebonyorgoldalone。But，gentlemen，wewantthesamematter；youaretoalternothingbuttheshape，and，therefore，havethegoodnesstoremovethisair，whichmaybedonesimplybywashingthesurfaceoftheboard，forthewaterhavingoncegotbetweentheboardandtheairwillruntogether，andtheebonywillgotothebottom；andifitdoesnot，youhavewontheday。
　　"ButmethinksIhearsomeofmyantagonistscunninglyopposingthis，andtellingmethattheywillnotonanyaccountallowtheirboardstobewetted，becausetheweightofthewatersoadded，bymakingitheavierthanitwasbefore，drawsittothebottom，andthattheadditionofnewweightiscontrarytoouragreement，whichwasthatthemattershouldbethesame。
　　"TothisIanswer，first，thatnobodycansupposebodiestobeputintothewaterwithouttheirbeingwet，nordoIwishtodomoretotheboardthanyoumaydototheball。Moreover，itisnottruethattheboardsinksonaccountoftheweightofthewateraddedinthewashing；forIwillputtenortwentydropsonthefloatingboard，andsolongastheystandseparateitshallnotsink；butiftheboardbetakenoutandallthatwaterwipedoff，andthewholesurfacebathedwithonesingledrop，andputitagainuponthewater，thereisnoquestionbutitwillsink，theotherwaterrunningtocoverit，beingnolongerhinderedbytheair。Inthenextplace，itisaltogetherfalsethatwatercaninanywayincreasetheweightofbodiesimmersedinit，forwaterhasnoweightinwater，sinceitdoesnotsink。Nowjustashewhoshouldsaythatbrassbyitsownnaturesinks，butthatwhenformedintotheshapeofakettleitacquiresfromthatfigurethevirtueoflyinginwaterwithoutsinking，wouldsaywhatisfalse，becausethatisnotpurelybrasswhichthenisputintothewater，butacompoundofbrassandair；soisitneithermorenorlessfalsethatathinplateofbrassorebonyswimsbyvirtueofitsdilatedandbroadfigure。Also，Icannotomittotellmyopponentsthatthisconceitofrefusingtobathethesurfaceoftheboardmightbegetanopinioninathirdpersonofapovertyofargumentontheirside，especiallyastheconversationbeganaboutflakesofice，inwhichitwouldbesimpletorequirethatthesurfacesshouldbekeptdry；nottomentionthatsuchpiecesofice，whetherwetordry，alwaysfloat，andsomyantagonistssay，becauseoftheirshape。
　　"SomemaywonderthatIaffirmthispowertobeintheairofkeepingplateofbrassorsilverabovewater，asifinacertainsenseIwouldattributetotheairakindofmagneticvirtueforsustainingheavybodieswithwhichitisincontact。TosatisfyallthesedoubtsIhavecontrivedthefollowingexperimenttodemonstratehowtrulytheairdoessupportthesebodies；forI
　　havefound，whenoneofthesebodieswhichfloatswhenplacedlightlyonthewateristhoroughlybathedandsunktothebottom，thatbycarryingdowntoitalittleairwithoutotherwisetouchingitintheleast，Iamabletoraiseandcarryitbacktothetop，whereitfloatsasbefore。Tothiseffect，Itakeaballofwax，andwithalittleleadmakeitjustheavyenoughtosinkveryslowlytothebottom，takingcarethatitssurfacebequitesmoothandeven。This，ifputgentlyintothewater，submergesalmostentirely，thereremainingvisibleonlyalittleoftheverytop，which，solongasitisjoinedtotheair，keepstheballafloat；butifwetakeawaythecontactoftheairbywettingthistop，theballsinkstothebottomandremainsthere。
　　Nowtomakeitreturntothesurfacebyvirtueoftheairwhichbeforesustainedit，thrustintothewateraglasswiththemouthdownward，whichwillcarrywithittheairitcontains，andmovethisdowntowardstheballuntilyousee，bythetransparencyoftheglass，thattheairhasreachedthetopofit；thengentlydrawtheglassupward，andyouwillseetheballrise，andafterwardsstayonthetopofthewater，ifyoucarefullyparttheglassandwaterwithouttoomuchdisturbingit。"[3]
　　ItwillbeseenthatGalileo，whileholdinginthemaintoacorrectthesis，yetmingleswithitsomefalseideas。Attheveryoutset，ofcourse，itisnottruethatwaterhasnoresistancetopenetration；itistrue，however，inthesenseinwhichGalileousestheterm——thatistosay，theresistanceofthewatertopenetrationisnotthedeterminingfactorordinarilyindecidingwhetherabodysinksorfloats。Yetinthecaseoftheflatbodyitisnotaltogetherinappropriatetosaythatthewaterresistspenetrationandthussupportsthebody。Themodernphysicistexplainsthephenomenonasduetosurface-tensionofthefluid。
　　Ofcourse，Galileo’sdisquisitiononthemixingofairwiththefloatingbodyisutterlyfanciful。Hisexperimentswerebeautifullyexact；histheorizingfromthemwas，inthisinstance，altogetherfallacious。Thus，asalreadyintimated，hispaperisadmirablyadaptedtoconveyadoublelessontothestudentofscience。
　　WILLIAMGILBERTANDTHESTUDYOFMAGNETISM
　　ItwillbeobservedthatthestudiesofGalileoandStevinuswerechieflyconcernedwiththeforceofgravitation。Meanwhile，therewasanEnglishphilosopherofcorrespondinggenius，whoseattentionwasdirectedtowardsinvestigationoftheequallymysteriousforceofterrestrialmagnetism。WiththedoubtfulexceptionofBacon，GilbertwasthemostdistinguishedmanofscienceinEnglandduringthereignofQueenElizabeth。Hewasformanyyearscourtphysician，andQueenElizabethultimatelysettleduponhimapensionthatenabledhimtocontinuehisresearchesinpurescience。
　　Hisinvestigationsinchemistry，althoughsupposedtobeofgreatimportance，aremostlylost；buthisgreatwork，DeMagnete，onwhichhelaboredforupwardsofeighteenyears，isaworkofsufficientimportance，asHallamsays，"toraisealastingreputationforitsauthor。"Fromitsfirstappearanceitcreatedaprofoundimpressionuponthelearnedmenofthecontinent，althoughinEnglandGilbert’stheoriesseemtohavebeensomewhatlessfavorablyreceived。Galileofreelyexpressedhisadmirationfortheworkanditsauthor；Bacon，whoadmiredtheauthor，didnotexpressthesameadmirationforhistheories；butDr。
　　Priestley，later，declaredhimtobe"thefatherofmodernelectricity。"
　　Strangelyenough，Gilbert’sbookhadneverbeentranslatedintoEnglish，orapparentlyintoanyotherlanguage，untilrecentyears，althoughatthetimeofitspublicationcertainlearnedmen，unabletoreadthebookintheoriginal，hadaskedthatitshouldbe。Bythisneglect，oroversight，agreatnumberofgeneralreadersaswellasmanyscientists，throughsucceedingcenturies，havebeendeprivedofthebenefitofwritingsthatcontainedagoodshareofthefundamentalfactsaboutmagnetismasknownto-day。
　　Gilbertwasthefirsttodiscoverthattheearthisagreatmagnet，andhenotonlygavethenameof"pole"totheextremitiesofthemagneticneedle，butalsospokeofthese"poles"asnorthandsouthpole，althoughheusedthesenamesintheoppositesensefromthatinwhichwenowusethem，hissouthpolebeingtheextremitywhichpointedtowardsthenorth，andviceversa。Hewasalsofirsttomakeuseoftheterms"electricforce，""electricemanations，"and"electricattractions。"
　　ItishardlynecessarytosaythatsomeoftheviewstakenbyGilbert，manyofhistheories，andtheaccuracyofsomeofhisexperimentshaveinrecenttimesbeenfoundtobeerroneous。Asapioneerinanunexploredfieldofscience，however，hisworkisremarkablyaccurate。"Onthewhole，"saysDr。JohnRobinson，"thisperformancecontainsmorerealinformationthananywritingoftheageinwhichhelived，andisscarcelyexceededbyanythathasappearedsince。"[4]
　　IntheprefacetohisworkGilbertsays:"Sinceinthediscoveryofsecretthings，andintheinvestigationofhiddencauses，strongerreasonsareobtainedfromsureexperimentsanddemonstratedargumentsthanfromprobableconjecturesandtheopinionsofphilosophicalspeculatorsofthecommonsort，therefore，totheendofthatnoblesubstanceofthatgreatloadstone，ourcommonmothertheearth，stillquiteunknown，andalsothattheforcesextraordinaryandexaltedofthisglobemaythebetterbeunderstood，wehavedecided，first，tobeginwiththecommonstonyandferruginousmatter，andmagneticbodies，andthepartoftheearththatwemayhandleandmayperceivewithsenses，andthentoproceedwithplainmagneticexperiments，andtopenetratetotheinnerpartsoftheearth。"[5]
　　Beforetakingupthedemonstrationthattheearthissimplyagiantloadstone，Gilbertdemonstratedinaningeniouswaythateveryloadstone，ofwhateversize，hasdefiniteandfixedpoles。
　　Hedidthisbyplacingthestoneinametallatheandconvertingitintoasphere，anduponthisspheredemonstratedhowthepolescanbefound。Tothisroundloadstonehegavethenameofterrella——thatis，littleearth。
　　"Tofind，then，polesansweringtotheearth，"hesays，"takeinyourhandtheroundstone，andlayonitaneedleorapieceofironwire:theendsofthewiremoveroundtheirmiddlepoint，andsuddenlycometoastandstill。Now，withochreorwithchalk，markwherethewireliesstillandsticks。Thenmovethemiddleorcentreofthewiretoanotherspot，andsotoathirdandfourth，alwaysmarkingthestonealongthelengthofthewirewhereitstandsstill；thelinessomarkedwillexhibitmeridiancircles，orcircleslikemeridians，onthestoneorterrella；andmanifestlytheywillallcometogetheratthepolesofthestone。
　　Thecirclebeingcontinuedinthisway，thepolesappear，boththenorthandthesouth，andbetwixtthese，midway，wemaydrawalargecircleforanequator，asisdonebytheastronomerintheheavensandonhisspheres，andbythegeographerontheterrestrialglobe。"[6]
　　Gilberthadtriedthefamiliarexperimentofplacingtheloadstoneonafloatinwater，andobservedthatthepolesalwaysrevolveduntiltheypointednorthandsouth，whichheexplainedasduetotheearth’smagneticattraction。Inthissameconnectionhenoticedthatapieceofwroughtironmountedonacorkfloatwasattractedbyothermetalstoaslightdegree，andheobservedalsothatanordinaryironbar，ifsuspendedhorizontallybyathread，assumesinvariablyanorthandsouthdirection。These，withmanyotherexperimentsofasimilarnature，convincedhimthattheearth"isamagnetandaloadstone，"whichhesaysisa"newandtillnowunheard-ofviewoftheearth。"
　　FullytoappreciateGilbert’srevolutionaryviewsconcerningtheearthasamagnet，itshouldberememberedthatnumberlesstheoriestoexplaintheactionoftheelectricneedlehadbeenadvanced。ColumbusandParacelsus，forexample，believedthatthemagnetwasattractedbysomepointintheheavens，suchasamagneticstar。Gilberthimselftellsofsomeofthebeliefsthathadbeenheldbyhispredecessors，manyofwhomhedeclares"wilfullyfalsify。"OneofhisfirststepswastorefutebyexperimentsuchassertionsasthatofCardan，that"awoundbyamagnetizedneedlewaspainless"；andalsotheassertionofFracastonithatloadstoneattractssilver；orthatofScalinger，thatthediamondwillattractiron；andthestatementofMatthiolusthat"ironrubbedwithgarlicisnolongerattractedtotheloadstone。"
　　Gilbertmadeextensiveexperimentstoexplainthedippingoftheneedle，whichhadbeenfirstnoticedbyWilliamNorman。Hisdeductionastothisphenomenonledhimtobelievethatthiswasalsoexplainedbythemagneticattractionoftheearth，andtopredictwheretheverticaldipwouldbefound。Thesedeductionsseemthemorewonderfulbecauseatthetimehemadethemthediphadjustbeendiscovered，andhadnotbeenstudiedexceptatLondon。Histheoryofthedipwas，therefore，ascientificprediction，basedonapreconceivedhypothesis。Gilbertfoundthediptobe72degreesatLondon；eightyearslaterHudsonfoundthedipat75degrees22’northlatitudetobe89degrees30’；
　　butitwasnotuntilovertwohundredyearslater，in1831，thattheverticaldipwasfirstobservedbySirJamesRossatabout70
　　degrees5’northlatitude，and96degrees43’westlongitude。
　　ThiswasnottheexactpointassumedbyGilbert，andhisscientificpredictions，therefore，werenotquitecorrect；butsuchcomparativelyslightandexcusableerrorsmarbutlittletheexcellenceofhisworkasawhole。
　　Abriefepitomeofsomeofhisotherimportantdiscoveriessufficestoshowthattheexaltedpositioninscienceaccordedhimbycontemporaries，aswellassucceedinggenerationsofscientists，waswellmerited。Hewasfirsttodistinguishbetweenmagnetismandelectricity，givingthelatteritsname。Hediscoveredalsothe"electricalcharge，"andpointedthewaytothediscoveryofinsulationbyshowingthatthechargecouldberetainedsometimeintheexcitedbodybycoveringitwithsomenon-conductingsubstance，suchassilk；although，ofcourse，electricalconductioncanhardlybesaidtohavebeenmorethanvaguelysurmised，ifunderstoodatallbyhim。Thefirstelectricalinstrumentevermade，andknownassuch，wasinventedbyhim，aswasalsothefirstmagnetometer，andthefirstelectricalindicatingdevice。Althoughthreecenturieshaveelapsedsincehisdeath，themethodofmagnetizingironfirstintroducedbyhimisincommonuseto-day。
　　Hemadeexhaustiveexperimentswithaneedlebalancedonapivottoseehowmanysubstanceshecouldfindwhich，likeamber，onbeingrubbedaffectedtheneedle。Inthiswayhediscoveredthatlightsubstanceswereattractedbyalum，mica，arsenic，sealing-wax，lacsulphur，slags，beryl，amethyst，rock-crystal，sapphire，jet，carbuncle，diamond，opal，Bristolstone，glass，glassofantimony，gum-mastic，hardresin，rock-salt，and，ofcourse，amber。Hediscoveredalsothatatmosphericconditionsaffectedtheproductionofelectricity，drynessbeingunfavorableandmoisturefavorable。
　　Galileo’sestimateofthisfirstelectricianistheverdictofsucceedinggenerations。"Iextremelyadmireandenvythisauthor，"hesaid。"Ithinkhimworthyofthegreatestpraiseforthemanynewandtrueobservationswhichhehasmade，tothedisgraceofsomanyvainandfablingauthors。"
　　STUDIESOFLIGHT，HEAT，ANDATMOSPHERICPRESSURE
　　WehaveseenthatGilbertwasbynomeanslackinginversatility，yettheinvestigationsuponwhichhisfameisfoundedwereallpursuedalongoneline，sothatthefatherofmagnetismmaybeconsideredoneoftheearliestofspecialistsinphysicalscience。Mostworkersofthetime，ontheotherband，extendedtheirinvestigationsinmanydirections。Thesumtotalofscientificknowledgeofthatdayhadnotbulkedsolargeastoexcludethepossibilitythatonemanmightmasteritall。SowefindaGalileo，forexample，makingrevolutionarydiscoveriesinastronomy，andperformingfundamentalexperimentsinvariousfieldsofphysics。Galileo’sgreatcontemporary，Kepler，wasalmostequallyversatile，thoughhisastronomicalstudieswereofsuchpre-eminentimportancethathisotherinvestigationssinkintorelativeinsignificance。Yetheperformedsomenotableexperimentsinatleastonedepartmentofphysics。Theseexperimentshadtodowiththerefractionoflight，asubjectwhichKeplerwasledtoinvestigate，inpartatleast，throughhisinterestinthetelescope。
　　WehaveseenthatPtolemyintheAlexandriantime，andAlhazen，theArab，madestudiesofrefraction。Keplerrepeatedtheirexperiments，and，strivingasalwaystogeneralizehisobservations，heattemptedtofindthelawthatgovernedtheobservedchangeofdirectionwhicharayoflightassumesinpassingfromonemediumtoanother。Keplermeasuredtheangleofrefractionbymeansofasimpleyetingenioustrough-likeapparatuswhichenabledhimtocomparereadilythedirectandrefractedrays。Hediscoveredthatwhenarayoflightpassesthroughaglassplate，ifitstrikesthefarthersurfaceoftheglassatananglegreaterthan45degreesitwillbetotallyrefractedinsteadofpassingthroughintotheair。Hecouldnotwellfailtoknowthatdifferentmediumsrefractlightdifferently，andthatforthesamemediumtheamountoflightvalieswiththechangeintheangleofincidence。Hewasnotable，however，togeneralizehisobservationsashedesired，andtothelastthelawthatgovernsrefractionescapedhim。ItremainedforWillebrordSnell，aDutchman，abouttheyear1621，todiscoverthelawinquestion，andforDescartes，alittlelater，toformulateit。Descartes，indeed，hassometimesbeensupposedtobethediscovererofthelaw。ThereisreasontobelievethathebasedhisgeneralizationsontheexperimentofSnell，thoughhedidnotopenlyacknowledgehisindebtedness。Thelaw，asDescartesexpressedit，statesthatthesineoftheangleofincidencebearsafixedratiotothesineoftheangleofrefractionforanygivenmedium。Here，then，wasanotherillustrationofthefactthatalmostinfinitelyvariedphenomenamaybebroughtwithinthescopeofasimplelaw。Oncethelawhadbeenexpressed，itcouldbetestedandverifiedwiththegreatestease；and，asusual，thediscoverybeingmade，itseemssurprisingthatearlierinvestigators——inparticularsosagaciousaguesserasKepler——shouldhavemissedit。
　　Galileohimselfmusthavebeentosomeextentastudentoflight，since，aswehaveseen，hemadesuchnotablecontributionstopracticalopticsthroughperfectingthetelescope；butheseemsnottohaveaddedanythingtothetheoryoflight。Thesubjectofheat，however，attractedhisattentioninasomewhatdifferentway，andhewasledtotheinventionofthefirstcontrivanceformeasuringtemperatures。Histhermometerwasbasedontheafterwardsfamiliarprincipleoftheexpansionofaliquidundertheinfluenceofheat；butasapracticalmeansofmeasuringtemperatureitwasaverycrudeaffair，becausethetubethatcontainedthemeasuringliquidwasexposedtotheair，hencebarometricchangesofpressurevitiatedtheexperiment。ItremainedforGalileo’sItaliansuccessorsoftheAccademiadelCimentoofFlorencetoimproveupontheapparatus，aftertheexperimentsofTorricelli——towhichweshallreferinamoment——hadthrownnewlightonthequestionofatmosphericpressure。StilllaterthecelebratedHuygenshitupontheideaofusingthemeltingandtheboilingpointofwaterasfixedpointsinascaleofmeasurements，whichfirstgavedefinitenesstothermometrictests。
　　TORRICELLI
　　IntheclosingyearsofhislifeGalileotookintohisfamily，ashisadopteddiscipleinscience，ayoungman，EvangelistaTorricelli1608-1647，whoprovedhimself，duringhisshortlifetime，tobeaworthyfollowerofhisgreatmaster。Notonlyworthyonaccountofhisgreatscientificdiscoveries，butgratefulaswell，forwhenhehadmadethegreatdiscoverythatthe"suction"madebyavacuumwasreallynothingbutairpressure，andnotsuctionatall，heregrettedthatsoimportantastepinsciencemightnothavebeenmadebyhisgreatteacher，Galileo，insteadofbyhimself。"ThisgenerosityofTorricelli，"
　　saysPlayfair，"was，perhaps，rarerthanhisgenius:therearemorewhomighthavediscoveredthesuspensionofmercuryinthebarometerthanwhowouldhavebeenwillingtopartwiththehonorofthediscoverytoamasterorafriend。"
　　Torricelli’sdiscoverywasmadein1643，lessthantwoyearsafterthedeathofhismaster。Galileohadobservedthatwaterwillnotriseinanexhaustedtube，suchasapump，toaheightgreaterthanthirty-threefeet，buthewasneverabletoofferasatisfactoryexplanationoftheprinciple。Torricelliwasabletodemonstratethattheheightatwhichthewaterstooddependeduponnothingbutitsweightascomparedwiththeweightofair。
　　Ifthisbetrue，itisevidentthatanyfluidwillbesupportedatadefiniteheight，accordingtoitsrelativeweightascomparedwithair。Thusmercury，whichisaboutthirteentimesmoredensethanwater，shouldonlyrisetoone-thirteenththeheightofacolumnofwater——thatis，aboutthirtyinches。
　　Reasoninginthisway，Torricelliproceededtoprovethathistheorywascorrect。Fillingalongtube，closedatoneend，withmercury，heinvertedthetubewithitsopenorificeinavesselofmercury。Thecolumnofmercuryfellatonce，butataheightofaboutthirtyinchesitstoppedandremainedstationary，thepressureoftheaironthemercuryinthevesselmaintainingitatthatheight。Thisdiscoverywasashatteringblowtotheoldtheorythathaddominatedthatfieldofphysicsforsomanycenturies。Itwascompletelyrevolutionarytoprovethat，insteadofamysterioussomethingwithinthetubebeingresponsibleforthesuspensionofliquidsatcertainheights，itwassimplytheordinaryatmosphericpressuremysteriousenough，itistrue——pushinguponthemfromwithout。Thepressureexertedbytheatmospherewasbutlittleunderstoodatthattime，butTorricelli’sdiscoveryaidedmateriallyinsolvingthemystery。
　　Thewholeclassofsimilarphenomenaofairpressure，whichhadbeenheldinthetrammeloflong-establishedbutfalsedoctrines，wasnowreducedtoonesimplelaw，andthedoortoasolutionofahostofunsolvedproblemsthrownopen。
　　Ithadlongbeensuspectedandbelievedthatthedensityoftheatmospherevariesatcertaintimes。Thattheairissometimes"heavy"andatothertimes"light"isapparenttothesenseswithoutscientificapparatusfordemonstration。Itisevident，then，thatTorricelli’scolumnofmercuryshouldriseandfalljustinproportiontothelightnessorheavinessoftheair。A
　　shortseriesofobservationsprovedthatitdidso，andwiththoseobservationswentnaturallytheobservationsastochangesintheweather。Itwasonlynecessary，therefore，toscratchascaleontheglasstube，indicatingrelativeatmosphericpressures，andtheTorricellianbarometerwascomplete。
　　Sucharevolutionarytheoryandsuchanimportantdiscoverywere，ofcourse，nottobeacceptedwithoutcontroversy，butthefeebleargumentsoftheopponentsshowedhowuntenabletheoldtheoryhadbecome。In1648Pascalsuggestedthatifthetheoryofthepressureofairuponthemercurywascorrect，itcouldbedemonstratedbyascendingamountainwiththemercurytube。Astheairwasknowntogetprogressivelylighterfrombasetosummit，theheightofthecolumnshouldbeprogressivelylessenedastheascentwasmade，andincreaseagainonthedescentintothedenserair。TheexperimentwasmadeonthemountaincalledthePuy-de-Dome，inAuvergne，andthecolumnofmercuryfellandroseprogressivelythroughaspaceofaboutthreeinchesastheascentanddescentweremade。
　　Thisexperimentpracticallysealedtheverdictonthenewtheory，butitalsosuggestedsomethingmore。Ifthemercurydescendedtoacertainmarkonthescaleonamountain-topwhoseheightwasknown，whywasnotthisameansofmeasuringtheheightsofallotherelevations？Andsothebeginningwasmadewhich，withcertainmodificationsandcorrectionsindetails，isnowthebasisofbarometricalmeasurementsofheights。
　　Inhydraulics，also，Torricelliseemstohavetakenoneofthefirststeps。Hedidthisbyshowingthatthewaterwhichissuesfromaholeinthesideorbottomofavesseldoessoatthesamevelocityasthatwhichabodywouldacquirebyfallingfromthelevelofthesurfaceofthewatertothatoftheorifice。Thisdiscoverywasofthegreatestimportancetoacorrectunderstandingofthescienceofthemotionsoffluids。Healsodiscoveredthevaluablemechanicalprinciplethatifanynumberofbodiesbeconnectedsothatbytheirmotionthereisneitherascentnordescentoftheircentreofgravity，thesebodiesareinequilibrium。
　　Besidesmakingthesediscoveries，hegreatlyimprovedthemicroscopeandthetelescope，andinventedasimplemicroscopemadeofaglobuleofglass。In1644hepublishedatractonthepropertiesofthecycloidinwhichhesuggestedasolutionoftheproblemofitsquadrature。AssoonasthispamphletappeareditsauthorwasaccusedbyGillesRoberval1602-1675ofhavingappropriatedasolutionalreadyofferedbyhim。Thisledtoalongdebate，duringwhichTorricelliwasseizedwithafever，fromtheeffectsofwhichhedied，inFlorence，October25，1647。
　　Thereisreasontobelieve，however，thatwhileRoberval’sdiscoverywasmadebeforeTorricelli’s，thelatterreachedhisconclusionsindependently。
　　VI。TWOPSEUDO-SCIENCES——ALCHEMYANDASTROLOGY
　　Inrecentchapterswehaveseensciencecomeforwardwithtremendousstrides。Aneweraisobviouslyathand。Butweshallmisconceivethespiritofthetimesifwefailtounderstandthatinthemidstofallthisprogresstherewasstillroomformediaevalsuperstitionandforthepursuitoffallaciousideals。
　　Twoformsofpseudo-sciencewerepeculiarlyprevalent——alchemyandastrology。Neitherofthesecanwithfullproprietybecalledascience，yetbothwerepursuedbymanyofthegreatestscientificworkersoftheperiod。Moreover，thestudiesofthealchemistmaywithsomeproprietybesaidtohavelaidthefoundationforthelatter-dayscienceofchemistry；whileastrologywascloselyalliedtoastronomy，thoughitsrelationstothatsciencearenotasintimateashassometimesbeensupposed。
　　Justwhenthestudyofalchemybeganisundetermined。Itwascertainlyofveryancientorigin，perhapsEgyptian，butitsmostflourishingtimewasfromabouttheeighthcenturyA。D。totheeighteenthcentury。ThestoriesoftheOldTestamentformedabasisforsomeofthestrangebeliefsregardingthepropertiesofthemagic"elixir，"or"philosopher’sstone。"Alchemistsbelievedthatmostoftheantediluvians，perhapsallofthem，possessedaknowledgeofthisstone。How，otherwise，couldtheyhaveprolongedtheirlivestonineandahalfcenturies？AndMoseswassurelyafirst-ratealchemist，asisprovedbythestoryoftheGoldenCalf。[1]AfterAaronhadmadethecalfofgold，Mosesperformedthemuchmoredifficulttaskofgrindingittopowderand"strewingituponthewaters，"thusshowingthathehadtransmuteditintosomelightersubstance。
　　ButantediluviansandBiblicalcharacterswerenottheonlypersonswhowerethoughttohavediscoveredthecoveted。
　　"elixir。"Hundredsofagedmediaevalchemistswerecreditedwithhavingmadethediscovery，andwerethoughttobelivingonthroughthecenturiesbyitsmeans。AlaiesdeLisle，forexample，whodiedin1298，attheageof110，wasallegedtohavebeenatthepointofdeathattheageoffifty，butjustatthistimehemadethefortunatediscoveryofthemagicstone，andsocontinuedtoliveinhealthandaffluenceforsixtyyearsmore。AndDeLislewasbutonecaseamonghundreds。
　　Anagedandwealthyalchemistcouldclaimwithseemingplausibilitythathewasprolonginghislifebyhismagic；
　　whereasayoungermanmightassertthat，knowingthegreatsecret，hewaskeepinghimselfyoungthroughthecenturies。Ineithercasesuchastatement，orrumor，aboutalearnedandwealthyalchemistwaslikelytobebelieved，particularlyamongstrangers；andassuchamanwould，ofcourse，betheobjectofmuchattention，theclaimwasfrequentlymadebypersonsseekingnotoriety。OneofthemostcelebratedoftheseimpostorswasacertainCountdeSaint-Germain，whowasconnectedwiththecourtofLouisXV。Hisstatementscarriedthemoreweightbecause，havingapparentlynomeansofmaintenance，hecontinuedtoliveinaffluenceyearafteryear——fortwothousandyears，ashehimselfadmitted——bymeansofthemagicstone。Ifatanytimehisstatementsweredoubted，hewasinthehabitofreferringtohisvaletforconfirmation，thisvaletbeingalsoundertheinfluenceoftheelixiroflife。
　　"Upononeoccasionhismasterwastellingapartyofladiesandgentlemen，atdinner，someconversationhehadhadinPalestine，withKingRichardI。，ofEngland，whomhedescribedasaveryparticularfriendofhis。Signsofastonishmentandincredulitywerevisibleonthefacesofthecompany，uponwhichSaint-Germainverycoollyturnedtohisservant，whostoodbehindhischair，andaskedhimifhehadnotspokenthetruth。’I
　　reallycannotsay，’repliedtheman，withoutmovingamuscle；
　　’youforget，sir，Ihavebeenonlyfivehundredyearsinyourservice。’’Ah，true，’saidhismaster，’Iremembernow；itwasalittlebeforeyourtime！’"[2]
　　InthetimeofSaint-Germain，onlyalittleoveracenturyago，beliefinalchemyhadalmostdisappeared，andhisextraordinarytaleswereprobablyregardedinthelightofamusingstories。
　　Stilltherewasundoubtedlyalingeringsuspicioninthemindsofmanythatthismanpossessedsomepeculiarsecret。Afewcenturiesearlierhistaleswouldhardlyhavebeenquestioned，foratthattimethebeliefintheexistenceofthismagicsomethingwassostrongthatthesearchforitbecamealmostaformofmania；andonceamanwasseizedwithit，liegambledawayhealth，position，andlifeitselfinpursuingthecovetedstake。AnexampleofthisisseeninAlbertusMagnus，oneofthemostlearnedmenofhistime，whoitissaidresignedhispositionasbishopofRatisboninorderthathemightpursuehisresearchesinalchemy。
　　Ifself-sacrificewasnotsufficienttosecuretheprize，crimewouldnaturallyfollow，fortherecouldbenolimittothepriceofthestakesinthisgame。ThenotoriousMarechaldeReys，failingtofindthecovetedstonebyordinarymethodsoflaboratoryresearch，waspersuadedbyanimpostorthatifhewouldpropitiatethefriendshipofthedevilthesecretwouldberevealed。TothisendDeReysbegansecretlycapturingyoungchildrenastheypassedhiscastleandmurderingthem。Whenhewasatlastbroughttojusticeitwasprovedthathehadmurderedsomethinglikeahundredchildrenwithinaperiodofthreeyears。
　　So，atleast，runsoneversionofthestoryofthispervertedbeing。
　　Naturallymonarchs，constantlyinneedoffunds，wereinterestedinthesealchemists。EvensoberEnglanddidnotescape，andRaymondLully，oneofthemostfamousofthethirteenthandfourteenthcenturyalchemists，issaidtohavebeensecretlyinvitedbyKingEdwardI。orII。toleaveMilanandsettleinEngland。Accordingtosomeaccounts，apartmentswereassignedtohisuseintheTowerofLondon，whereheisallegedtohavemadesomesixmillionpoundssterlingforthemonarch，outofiron，mercury，lead，andpewter。
　　PopeJohnXXII。，afriendandpupilofthealchemistArnolddeVilleneuve，isreportedtohavelearnedthesecretsofalchemyfromhismaster。Laterheissuedtwobullsagainst"pretenders"
　　intheart，which，farfromshowinghisdisbelief，werecitedbyalchemistsasprovingthatherecognizedpretendersasdistinctfromtruemastersofmagic。
　　Tomodernstheattitudeofmindofthealchemistisdifficulttocomprehend。Itis，perhaps，possibletoconceiveofanimalsorplantspossessingsouls，buttheearlyalchemistattributedthesamething——orsomethingkintoit——tometalsalso。Furthermore，justasplantsgerminatedfromseeds，sometalsweresupposedtogerminatealso，andhenceaconstantgrowthofmetalsintheground。Toprovethisthealchemistcitedcaseswherepreviouslyexhaustedgold-mineswerefound，afteralapseoftime，tocontainfreshquantitiesofgold。The"seed"oftheremainingparticlesofgoldhadmultipliedandincreased。Butthisgerminatingprocesscouldonlytakeplaceunderfavorableconditions，justastheseedofaplantmusthaveitspropersurroundingsbeforegerminating；anditwasbelievedthattheactionofthephilosopher’sstonewastohastenthisprocess，asmanmayhastenthegrowthofplantsbyartificialmeans。Goldwaslookeduponasthemostperfectmetal，andallothermetalsimperfect，becausenotyet"purified。"Bysomealchemiststheywereregardedaslepers，who，whencuredoftheirleprosy，wouldbecomegold。Andsincenatureintendedthatallthingsshouldbeperfect，itwastheaimofthealchemisttoassistherinthispurifyingprocess，andincidentallytogainwealthandprolonghislife。
　　Byotheralchemiststheprocessoftransitionfrombasermetalsintogoldwasconceivedtobelikeaprocessofripeningfruit。
　　Theripenedproductwasgold，whilethegreenfruit，invariousstagesofmaturity，wasrepresentedbythebasemetals。Silver，forexample，wasmorenearlyripethanlead；butthedifferencewasonlyoneof"digestion，"anditwasthoughtthatbyfurther"digestion"leadmightfirstbecomesilverandeventuallygold。
　　Inotherwords，Naturehadnotcompletedherwork，andwaswofullyslowatitatbest；butman，withhissuperiorfaculties，wastohastentheprocessinhislaboratories——ifhecouldbuthitupontherightmethodofdoingso。
　　Itshouldnotbeinferredthatthealchemistsetabouthistaskofassistingnatureinahaphazardway，andwithouttraininginthevariousalchemiclaboratorymethods。Onthecontrary，heusuallyservedalongapprenticeshipintherudimentsofhiscalling。Hewasobligedtolearn，inageneralway，manyofthesamethingsthatmustbeunderstoodineitherchemicaloralchemicallaboratories。Thegeneralknowledgethatcertainliquidsvaporizeatlowertemperaturesthanothers，andthatthemelting-pointsofmetalsdiffergreatly，forexample，wasjustasnecessarytoalchemyastochemistry。Theknowledgeofthegrossstructure，ornature，ofmaterialswasmuchthesametothealchemistastothechemist，and，forthatmatter，manyoftheexperimentsincalcining，distilling，etc。，werepracticallyidentical。
　　Tothealchemisttherewerethreeprinciples——salt，sulphur，andmercury——andthesourcesoftheseprincipleswerethefourelements——earth，water，fire，andair。Thesefourelementswereaccountableforeverysubstanceinnature。Someoftheexperimentstoprovethisweresoillusive，andyetapparentlysosimple，thatoneisnotsurprisedthatittookcenturiestodisprovethem。Thatwaterwascomposedofearthandairseemedeasilyprovenbythesimpleprocessofboilingitinatea-kettle，fortheresidueleftwasobviouslyanearthysubstance，whereasthesteamdrivenoffwassupposedtobeair。
　　Thefactthatpurewaterleavesnoresiduewasnotdemonstrateduntilafteralchemyhadpracticallyceasedtoexist。Itwaspossiblealsotodemonstratethatwatercouldbeturnedintofirebythrustingared-hotpokerunderabellglasscontainingadishofwater。Notonlydidthequantityofwaterdiminish，but，ifalightedcandlewasthrustundertheglass，thecontentsignitedandburned，proving，apparently，thatwaterhadbeenconvertedintofire。These，andscoresofothersimilarexperiments，seemedsoeasilyexplained，andtoaccordsowellwiththe"fourelements"theory，thattheywereseldomquestioneduntilalaterageofinductivescience。
　　Buttherewasoneexperimenttowhichthealchemistpinnedhisfaithinshowingthatmetalscouldbe"killed"and"revived，"
　　whenpropermeanswereemployed。Ithadbeenknownformanycenturiesthatifanymetal，otherthangoldorsilver，werecalcinedinanopencrucible，itturned，afteratime，intoapeculiarkindofash。Thisashwasthoughtbythealchemisttorepresentthedeathofthemetal。Butiftothissameashafewgrainsofwheatwereaddedandheatagainappliedtothecrucible，themetalwasseento"risefromitsashes"andresumeitsoriginalform——awell-knownphenomenonofreducingmetalsfromoxidesbytheuseofcarbon，intheformofwheat，or，forthatmatter，anyothercarbonaceoussubstance。Wheatwas，therefore，madethesymboloftheresurrectionofthelifeeternal。Oats，corn，orapieceofcharcoalwouldhave"revived"
　　themetalsfromtheashesequallywell，butthemediaevalalchemistseemsnottohaveknownthis。However，inthisexperimentthemetalseemedactuallytobedestroyedandrevivified，and，assciencehadnotasyetexplainedthisstrikingphenomenon，itislittlewonderthatitdeceivedthealchemist。
　　Sincethealchemistspursuedtheirsearchofthemagicstoneinsuchamethodicalway，itwouldseemthattheymusthavesomeideaoftheappearanceofthesubstancetheysought。Probablytheydid，eachaccordingtohisownmentalbias；but，ifso，theyseldomcommittedthemselvestowriting，confiningtheirdiscourseslargelytospeculationsastothepropertiesofthisillusivesubstance。Furthermore，thedesireforsecrecywouldpreventthemfromexpressingsoimportantapieceofinformation。
　　Butonthesubjectoftheproperties，ifnotontheappearanceofthe"essence，"theywerevoluminouswriters。Itwassupposedtobetheonlyperfectsubstanceinexistence，andtobeconfinedinvarioussubstances，inquantitiesproportionatetothestateofperfectionofthesubstance。Thus，goldbeingmostnearlyperfectwouldcontainmore，silverless，leadstillless，andsoon。The"essence"containedinthemorenearlyperfectmetalswasthoughttobemorepotent，averysmallquantityofitbeingcapableofcreatinglargequantitiesofgoldandofprolonginglifeindefinitely。
　　Itwouldappearfrommanyofthewritingsofthealchemiststhattheirconceptionofnatureandthesupernaturalwassoconfusedandentangledinaninexplicablephilosophythattheythemselvesdidnotreallyunderstandthemeaningofwhattheywereattemptingtoconvey。Butitshouldnotbeforgottenthatalchemywaskeptasmuchaspossiblefromtheignorantgeneralpublic，andthealchemiststhemselveshadknowledgeofsecretwordsandexpressionswhichconveyedadefinitemeaningtooneoftheirnumber，butwhichwouldappearameaninglessjumbletoanoutsider。Someofthesewritersdeclaredopenlythattheirwritingswereintendedtoconveyanentirelyerroneousimpression，andweresentoutonlyforthatpurpose。
　　However，whileitmayhavebeentruethatthevagariesoftheirwritingsweremadepurposely，thecaseisprobablymorecorrectlyexplainedbysayingthattheverynatureoftheartmadedefinitestatementsimpossible。Theyweredealingwithsomethingthatdidnotexist——couldnotexist。Theirattempteddescriptionsbecame，therefore，thelanguageofromanceratherthanthelanguageofscience。
　　Butifthealchemiststhemselveswereusuallysilentastotheappearanceoftheactualsubstanceofthephilosopher’sstone，therewerenumberlessotherwriterswhowerelessreticent。Bysomeitwassupposedtobeastone，byothersaliquidorelixir，butmorecommonlyitwasdescribedasablackpowder。Italsopossesseddifferentdegreesofefficiencyaccordingtoitsdegreesofpurity，certainformsonlypossessingthepowerofturningbasemetalsintogold，whileothersgaveeternalyouthandlifeordifferentdegreesofhealth。Thusanalchemist，whohadmadeapartialdiscoveryofthissubstance，couldprolonglifeacertainnumberofyearsonly，or，possessingonlyasmallandinadequateamountofthemagicpowder，hewasobligedtogiveuptheghostwhentheeffectofthissmallquantityhadpassedaway。
　　Thisbeliefinthesupernaturalpowerofthephilosopher’sstonetoprolonglifeandhealdiseaseswasprobablyalaterphaseofalchemy，possiblydevelopedbyattemptstoconnectthepowerofthemysteriousessencewithBiblicalteachings。TheearlyRomanalchemists，whoclaimedtobeabletotransmutemetals，seemnottohavemadeotherclaimsfortheirmagicstone。
　　Bythefifteenthcenturythebeliefinthephilosopher’sstonehadbecomesofixedthatgovernmentsbegantobealarmedlestsomeluckypossessorofthesecretshouldfloodthecountrywithgold，thusrenderingtheexistingcoinoflittlevalue。Somelittleconsolationwasfoundinthethoughtthatincaseallthebasermetalswereconvertedintogoldironwouldthenbecomethe"preciousmetal，"andwouldremainsountilsomenewphilosopher’sstonewasfoundtoconvertgoldbackintoiron——amuchmoredifficultfeat，itwasthought。However，tobeonthesafeside，theEnglishParliament，in1404，sawfittopassanactdeclaringthemakingofgoldandsilvertobeafelony。
　　Nevertheless，in1455，KingHenryVI。grantedpermissiontoseveral"knights，citizensofLondon，chemists，andmonks"tofindthephilosopher’sstone，orelixir，thatthecrownmightthusbeenabledtopayoffitsdebts。Themonksandecclesiasticsweresupposedtobemostlikelytodiscoverthesecretprocess，since"theyweresuchgoodartistsintransubstantiatingbreadandwine。"
　　InGermanytheemperorsMaximilianI。，RudolfII。，andFrederickII。gaveconsiderableattentiontothesearch，andtheexampletheysetwasfollowedbythousandsoftheirsubjects。Itissaidthatsomenoblemendevelopedtheunpleasantcustomofinvitingtotheircourtsmenwhowerereputedtohavefoundthestone，andthenimprisoningthepooralchemistsuntiltheyhadmadeacertainquantityofgold，stimulatingtheiractivitywithtorturesofthemostatrociouskinds。Thusthisdangerofbeingimprisonedandheldforransomuntilsomefabulousamountofgoldshouldbemadebecametheconstantmenaceofthealchemist。Itwasuselessforanalchemisttopleadpovertyonceitwasnoisedaboutthathehadlearnedthesecret。Forhowcouldsuchamanbepoorwhen，withapieceofmetalandafewgrainsofmagicpowder，hewasabletoprovidehimselfwithgold？Itwas，therefore，arecklessalchemistindeedwhodaredboastthathehadmadethecoveteddiscovery。
　　Thefateofacertainindiscreetalchemist，supposedbymanytohavebeenSeton，aScotchman，wasnotanuncommonone。WordhavingbeenbroughttotheelectorofSaxonythatthisalchemistwasinDresdenandboastingofhispowers，theelectorcausedhimtobearrestedandimprisoned。Fortyguardswerestationedtoseethathedidnotescapeandthatnoonevisitedhimsavetheelectorhimself。Forsometimetheelectortriedbyargumentandpersuasiontopenetratehissecretortoinducehimtomakeacertainquantityofgold；butasSetonsteadilyrefused，therackwastried，andforseveralmonthshesufferedtorture，untilfinally，reducedtoamereskeleton，bewasrescuedbyarivalcandidateoftheelector，aPolenamedMichaelSendivogins，whodruggedtheguards。However，beforeSetoncouldbe"persuaded"byhisnewcaptor，hediedofhisinjuries。
　　ButSendivoginswasalsoambitiousinalchemy，and，sinceSetonwasbeyondhisreach，hetookthenextbeststepandmarriedhiswidow。Fromher，asthestorygoes，hereceivedanounceofblackpowder——theveritablephilosopher’sstone。Withthishemanufacturedgreatquantitiesofgold，eveninvitingEmperorRudolfII。toseehimworkthemiracle。Thatmonarchwassoimpressedthathecausedatablettobeinsertedinthewalloftheroominwhichhehadseenthegoldmade。
　　SendivoginshadlearneddiscretionfromthemisfortuneofSeton，sothathetooktheprecautionofconcealingmostofthepreciouspowderinasecretchamberofhiscarriagewhenhetravelled，havingonlyasmallquantitycarriedbyhisstewardinagoldbox。Inparticularlydangerousplaces，heissaidtohaveexchangedclotheswithhiscoachman，makingtheservanttakehisplaceinthecarriagewhilehemountedthebox。
　　AboutthemiddleoftheseventeenthcenturyalchemytooksuchfirmrootinthereligiousfieldthatitbecamethebasisofthesectknownastheRosicrucians。ThenamewasderivedfromtheteachingofaGermanphilosopher，Rosenkreutz，who，havingbeenhealedofadangerousillnessbyanArabiansupposedtopossessthephilosopher’sstone，returnedhomeandgatheredabouthimachosenbandoffriends，towhomheimpartedthesecret。Thissectcamerapidlyintoprominence，andforashorttimeatleastcreatedasensationinEurope，andatthetimewerecreditedwithhaving"refinedandspiritualized"alchemy。Butbytheendoftheseventeenthcenturytheirnumberhaddwindledtoamerehandful，andhenceforththeyexertedlittleinfluence。
　　AnotherandearlierreligioussectwastheAureacrucians，foundedbyJacobBohme，ashoemaker，borninPrussiain1575。Accordingtohisteachingsthephilosopher’sstonecouldbediscoveredbyadiligentsearchoftheOldandtheNewTestaments，andmoreparticularlytheApocalypse，whichcontainedallthesecretsofalchemy。ThissectfoundquiteanumberoffollowersduringthelifeofBohme，butgraduallydiedoutafterhisdeath；not，however，untilmanyofitsmembershadbeentorturedforheresy，andoneatleast，Kuhlmann，ofMoscow，burnedasasorcerer。
　　Thenamesofthedifferentsubstancesthatatvarioustimeswerethoughttocontainthelargequantitiesofthe"essence"duringthemanycenturiesofsearchingforit，formalistofpracticallyallsubstancesthatwereknown，discovered，orinventedduringtheperiod。Somebelievedthatacidscontainedthesubstance；otherssoughtitinmineralsorinanimalorvegetableproducts；whilestillotherslookedtofinditamongthedistilled"spirits"——thealcoholicliquorsanddistilledproducts。OntheintroductionofalcoholbytheArabsthatsubstancebecameofall-absorbinginterest，andforalongtimealluredthealchemistintobelievingthatthroughittheyweresoontoberewarded。Theyrectifiedandrefinedituntil"sometimesitwassostrongthatitbrokethevesselscontainingit，"butstillitfailedinitsmagicpower。Later，brandywassubstitutedforit，andthisinturndiscardedformorerecentdiscoveries。
　　Therewerealways，ofcourse，twoclassesofalchemists:seriousinvestigatorswhosehonestycouldnotbequestioned，andcleverimpostorswhoselegerdemainwasprobablylargelyresponsiblefortheextendedbeliefintheexistenceofthephilosopher’sstone。
　　Sometimesanalchemistpractisedboth，usingtheprofitsofhissleight-of-handtoprocurethemeansofcarryingonhisseriousalchemicalresearches。Theimposturesofsomeofthesejugglersdeceivedeventhemostintelligentandlearnedmenofthetime，andsokepttheflameofhopeconstantlyburning。Theageofcoldinvestigationhadnotarrived，anditiseasytounderstandhowanunscrupulousmediaevalHermannorKellarmightcompletelydeceiveeventhemostintelligentandthoughtfulscholars。Inscoffingatthecredulityofsuchanage，itshouldnotbeforgottenthatthe"Keelymotor"wasalatenineteenth-centuryillusion。
　　Butlongbeforethebeliefinthephilosopher’sstonehaddiedout，themethodsofthelegerdemainalchemisthadbeeninvestigatedandreporteduponofficiallybybodiesofmenappointedtomakesuchinvestigations，althoughittookseveralgenerationscompletelytooverthrowasuperstitionthathadbeenhandeddownthroughseveralthousandyears。InAprilof1772
　　MonsieurGeoffroymadeareporttotheRoyalAcademyofSciences，atParis，onthealchemiccheatsprincipallyofthesixteenthandseventeenthcenturies。Inthisreportheexplainsmanyoftheseeminglymarvellousfeatsoftheunscrupulousalchemists。Averycommonformofdeceptionwastheuseofadouble-bottomedcrucible。Acopperorbrasscruciblewascoveredontheinsidewithalayerofwax，cleverlypaintedsoastoresembletheordinarymetal。Betweenthislayerofwaxandthebottomofthecrucible，however，wasalayerofgolddustorsilver。Whenthealchemistwishedtodemonstratehispower，hehadbuttoplacesomemercuryorwhateversubstancehechoseinthecrucible，heatit，throwinagrainortwoofsomemysteriouspowder，pronounceafewequallymysteriousphrasestoimpresshisaudience，and，behold，alumpofpreciousmetalwouldbefoundinthebottomofhispot。Thiswasthefavoritemethodofmediocreperformers，butwas，ofcourse，easilydetected。
　　Anequallysuccessfulbutmoredifficultwaywastoinsertsurreptitiouslyalumpofmetalintothemixture，usinganordinarycrucible。Thisrequiredgreatdexterity，butwasfacilitatedbytheuseofmanymysteriousceremoniesonthepartoftheoperatorwhileperforming，justasthemodernvaudevilleperformerdivertstheattentionoftheaudiencetohisrighthandwhilehisleftisengagedinthetrick。Suchceremonieswerenotquestioned，foritwasthecommonbeliefthatthewholeprocess"layinthespiritasmuchasinthesubstance，"many，aswehaveseen，regardingthewholeprocessasadivinemanifestation。
　　Sometimesahollowrodwasusedforstirringthemixtureinthecrucible，thisrodcontaininggolddust，andhavingtheendpluggedeitherwithwaxorsoftmetalthatwaseasilymelted。
　　Again，piecesofleadwereusedwhichhadbeenpluggedwithlumpsofgoldcarefullycoveredover；andaverysimpleandimpressivedemonstrationwasmakinguseofanuggetofgoldthathadbeencoatedoverwithquicksilverandtarnishedsoastoresembleleadorsomebasemetal。Whenthiswasthrownintoacidthecoatingwasremovedbychemicalaction，leavingtheshiningmetalinthebottomofthevessel。Inordertoperformsomeofthesetricks，itisobviousthatthealchemistmusthavebeenwellsuppliedwithgold，assomeofthem，whenperformingbeforearoyalaudience，gavetheproductstotheirvisitors。Butitwasalwaysapayinginvestment，foroncehisreputationwasestablishedthegold-makerfoundanendlessvarietyofwaysofturninghisallegedknowledgetoaccount，frequentlyamassinggreatwealth。
　　Someofthecleverestofthecharlatansofteninvitedroyalorotherdistinguishedgueststobringwiththemironnailstobeturnedintogoldones。Theyweretransmutedinthealchemist’scruciblebeforetheeyesofthevisitors，thejuggleradroitlyextractingtheironnailandinsertingagoldonewithoutdetection。Itmatteredlittleiftheconvertedgoldnaildifferedinsizeandshapefromtheoriginal，forthischangeinshapecouldbelaidtotheprocessoftransmutation；andeventheverycriticalwerehardlylikelytofindfaultwiththeexchangethusmade。Furthermore，itwasbelievedthatgoldpossessedthepropertyofchangingitsbulkundercertainconditions，someofthemoreconservativealchemistsmaintainingthatgoldwasonlyincreasedinbulk，notnecessarilycreated，bycertainformsofthemagicstone。Thusaveryproficientoperatorwasthoughttobeabletoincreaseagrainofgoldintoapoundofpuremetal，whileonelessexpertcouldonlydouble，orpossiblytreble，itsoriginalweight。
　　Theactualnumberofusefuldiscoveriesresultingfromtheeffortsofthealchemistsisconsiderable，someofthemofincalculablevalue。RogerBacon，wholivedinthethirteenthcentury，whiledevotingmuchofhistimetoalchemy，madesuchvaluablediscoveriesasthetheory，atleast，ofthetelescope，andprobablygunpowder。Ofthislatterwecannotbesurethatthediscoverywashisownandthathehadnotlearnedofitthroughthesourceofoldmanuscripts。Butitisnotimpossiblenorimprobablethathemayhavehituponthemixturethatmakestheexplosiveswhilesearchingforthephilosopher’sstoneinhislaboratory。"VonHelmont，inthesamepursuit，discoverdthepropertiesofgas，"saysMackay；"Gebermadediscoveriesinchemistry，whichwereequallyimportant；andParacelsus，amidhisperpetualvisionsofthetransmutationofmetals，foundthatmercurywasaremedyforoneofthemostodiousandexcruciatingofallthediseasesthatafflicthumanity。"’Asweshallseealittlefartheron，alchemyfinallyevolvedintomodernchemistry，butnotuntilithadpassedthroughseveralimportanttransitionalstages。