——Theonlyquestionthereforeis，howfaritshouldbebroughtforward？——Theanswerisshort，andeasytobeunderstood；——bringitforwardasfaraspossible，withoutdiminishingtoomuchthepassagewhichmustbeleftforthesmoke。Nowasthispassage，which，initsnarrowestpart，IhavecalledtheTHROATOFTHE
CHIMNEY，ought，forreasonswhicharefullyexplainedintheforegoingChapter，tobeimmediately，orperpendicularlyovertheFire，itisevidentthatthebackoftheChimneymustalwaysbebuiltperfectlyupright——Todeterminethereforetheplaceforthenewback，orhowfarpreciselyitoughttobebroughtforward，nothingmoreisnecessarythantoascertainhowwidethethroatoftheChimneyoughttobeleft，orwhatspacemustbeleft，betweenthetopofthebreastoftheChimney，wheretheuprightcanaloftheChimneybegins，andthenewbackoftheFire-placecarriedupperpendicularlytothatheight。
InthecourseofmynumerousexperimentsuponChimnies，Ihavetakenmuchpainstodeterminethewidthpropertobegiventothispassage，andIhavefound，that，whenthebackoftheFire-placeisofaproperwidth，thebestwidthforthethroatofaChimney，whentheChimneyandtheFire-placeareattheusualformandsize，isFOURINCHES——Threeinchesmightsometimesanswer，especiallywheretheFire-placeisverysmall，andtheChimneygood，andwellsituated：butasitisalwaysofmuchimportancetopreventthoseaccidentalpuffsofsmokewhicharesometimesthrownintoroomsbythecarelessnessofservantsinputtingonsuddenlytoomanycoalsatonceuponthefire，andasIfoundtheseaccidentssometimeshappenedwhenthethroatsofChimneysweremadeverynarrow，Ifoundthat，uponthewhole，allcircumstancesbeingwellconsidered，andadvantagesanddisadvantagescomparedandbalanced，FOURINCHESisthebestwidththatcanbegiventothethroatofachimney；andthis，whethertheFire-placebedestinedtoburnwood，coals，turf，oranyotherfuelcommonlyusedforheatingroomsbyanopenfire。
InFire-placesdestinedforheatingverylargehalls，andwhereverygreatfiresarekeptup，thethroatoftheChimneymay，ifitshouldbethoughtnecessary，bemadefourinchesandanhalf，orfiveincheswide；——butIhavefrequentlymadeFire-placesforhallswhichhaveansweredperfectlywellwherethethroatsoftheChimnieshavenotbeenwiderthanfourinches。
Itmayperhapsappearextraordinary，uponthefirstviewofthematter，thatFire-placesofsuchdifferentsizesshouldallrequirethethroatoftheChimneytobeofthesamewidth；butwhenitisconsideredthattheCAPACITYofthethroatofaChimneydoesnotdependonitswidthalone，butonitswidthandLENGTHtakentogether；andthatinlargeFire-places，thewidthoftheback，andconsequentlythelengthofthethroatoftheChimney，isgreaterthaninthosewhicharesmaller，thisdifficultyvanishes。
AndthisleadsustoconsideranotherimportantpointrespectingopenFire-places，andthatis，thewidthwhichitwill，ineachcase，bepropertogivetotheback——InFire-placesastheyarenowcommonlyconstructed，thebackisofequalwidthwiththeopeningoftheFire-placeinfront；——butthisconstructionisfaultyontwoaccounts——First，inaFire-place，soconstructed，thesidesoftheFire-place，orCOVINGS，astheyarecalled，areparalleltoeachother，andconsequentlyill-contrivedtothrowoutintotheroomtheheattheyreceivefromthefireintheformofrays；——andsecondly，thelargeopencornerswhichareformedbymakingthebackaswideastheopeningoftheFire-placeinfrontoccasioneddiesofwind，whichfrequentlydisturbthefire，andembarrassthesmokeinitsascentinsuchamannerasoftentobringitintotheroom——BoththesedefectsmaybeentirelyremediedbydiminishingthewidthofthebackoftheFire-place——
Thewidthwhich，inmostcases，itwillbebesttogiveit，isONETHIRDofthewidthoftheopeningoftheFire-placeinfront——Butitisnotabsolutelynecessarytoconformrigorouslytothisdecision，norwillitalwaysbepossible——ItwillfrequentlyhappenthatthebackofaChimneymustbemadewiderthan，accordingtotheruleheregiven，itoughttobe——Thismaybe，eithertoaccommodatetheFire-placetoastove，whichbeingalreadyonhand，must，toavoidtheexpenseofpurchasinganewone，beemployed；orforotherreasons；——andanysmalldeviationfromthegeneralrulewillbeattendedwithnoconsiderableinconvenience——Itwillalwaysbebest，however，toconformtoitasfarascircumstanceswillallow。
WhereaChimneyisdesignedforwarmingaroomofamiddlingsize，andwherethethicknessofthewalloftheChimneyinfront，measuredfromthefrontofthemantletothebreastoftheChimney，isnineinches，IshouldsetofffourinchesmoreforthewidthofthethroatoftheChimney，which，supposingthebackoftheChimneytobebuiltupright，asitalwaysoughttobe，willgivethirteeninchesforthedepthoftheFire-place，measureduponthehearth，fromtheopeningoftheFire-placeinfront，totheback——Inthiscasethirteenincheswouldbeagoodsizeforthewidthoftheback；andthreetimesthirteeninches，orthirty-nineinches，forthewidthoftheopeningoftheFire-placeinfront；andtheanglemadebythebackoftheFire-placeandthesidesofit，orcovings，wouldbejust135
degrees，whichisthebestpositiontheycanhaveforthrowingheatintotheroom。
ButIwillsupposethatinalteringsuchaChimneyitisfoundnecessary，inordertoaccommodatetheFire-placetoagrateorstovealreadyonhand，tomaketheFire-placesixteenincheswide——Inthatcase，Ishouldmerelyincreasethewidthoftheback，tothedimensionsrequired，withoutalteringthedepthoftheChimney，orincreasingthewidthoftheopeningoftheChimneyinfront——Thecovings，itistrue，wouldbesomewhatreducedintheirwidth，bythisalteration；andtheirpositionwithrespecttotheplaneofthebackoftheChimneywouldbealittlechanged；butthesealterationswouldproducenobadeffectsofanyconsiderableconsequence，andwouldbemuchlesslikelytoinjuretheFire-place，thananattempttobringtheproportionsofitspartsnearertothestandard，byincreasingthedepthoftheChimney，andthewidthofitsopeninginfront；——orthananattempttopreservethatparticularobliquityofthecovingswhichisrecommendedasthebest，135degrees，
byincreasingthewidthoftheopeningoftheFire-place，withoutincreasingitsdepth。
Inordertoillustratethissubjectmorefully，wewillsupposeonecasemore——WewillsupposethatintheChimneywhichistobealtered，thewidthoftheFire-placeinfrontiseitherwiderornarrowerthanitoughttobe，inorderthatthedifferentpartsoftheFire-place，afteritisaltered，maybeoftheproperdimensions。Inthiscase，IshoulddeterminethedepthoftheFire-place，andthewidthofthebackofit，withoutanyregardtothewidthoftheopeningoftheFire-placeinfront；
andwhenthisisdone，iftheopeningofFire-placeshouldbeonlytwoorthreeinchestoowide，thatistosay，onlytwoorthreeincheswiderthanisnecessaryinorderthatthecovingsmaybebroughtintotheirproperpositionwithrespecttotheback，Ishouldnotalterthewidthofthisopening，butshouldaccommodatethecovingstothiswidth，byincreasingtheirbreadth，andincreasingtheangletheymakewiththebackoftheFire-place；butiftheopeningoftheFire-placeshouldbemorethanthreeinchestoowide；——Ishouldreduceittotheproperwidthbyslipsofstone，orbybricksandmortar。
WhenthewidthoftheopeningoftheFire-place，infront，isverygreat，comparedwiththedepthoftheFire-place，andwiththewidthoftheback，thecovingsinthatcasebeingverywide，andconsequentlyveryoblique，andtheFire-placeveryshallow，anysuddenmotionoftheairinfrontoftheFire-place，thatmotion，forinstance，whichwouldbeoccasionedbytheclothesofawomanpassinghastilybeforethefire，andverynearit，
wouldbeapttocauseeddiesintheair，WITHINTHEOPENINGOF
THEFIRE-PLACE，bywhichpuffsofsmokemighteasilybebroughtintotheroom。ShouldtheopeningoftheChimneybetoonarrow，whichhoweverwillveryseldombefoundtobethecase，itwill，ingeneral，beadvisabletoletitremainasitis，andtoaccommodatethecovingstoit，rathertoattempttoincreaseitswidth，whichwouldbeattendedwithagooddealoftrouble，andprobablyaconsiderableexpence。
Fromallthathasbeensaiditisevident，thatthepointsofthegreatestimportance，andwhichoughtmostparticularlytobeattendedto，inalteringFire-placesupontheprincipleshererecommended，are，thebringingforwardthebacktoitsproperplace，andmakingitofaproperwidth——ButitistimethatI
shouldmentionanothermatteruponwhichitisprobablethatmyreaderisalreadyimpatienttoreceiveinformation——ProvisionmustbemadeforthepassageoftheChimney-sweeperuptheChimney——Thismayeasilybedoneinthefollowingmanner：——
InbuildingupthenewbackoftheFire-place；whenthiswall，whichneedneverbemorethanthewidthofasinglebrickinthickness，isbroughtupsohighthatthereremainsnomorethanabouttenoreleveninchesbetweenwhatisthenthetopofit，andtheinsideofthemantle，orlowerextremityofthebreastoftheChimney，anopening，ordoor-way，elevenortwelveincheswide，mustbebeguninthemiddleoftheback，andcontinuedquitetothetopofit，which，accordingtotheheighttowhichitwillcommonlybenecessarytocarryuptheback，willmaketheopeningabouttwelveorfourteenincheshigh；whichwillbequitesufficienttoallowtheChimney-sweepertopass。WhentheFire-placeisfinished，thisdoor-wayistobeclosedbyafewbricks，byatile，orafitpieceofstone，placedinit，dry，orwithoutmortar，andconfinedinitsplacebymeansofarabbetmadeforthatpurposeinthebrick-work——AsoftenastheChimneyisswept，theChimney-sweepertakesdownthistemporarywall，whichisveryeasilydone，andwhenhehasfinishedhiswork，heputsitagainintoitsplace——TheannexeddrawingNo。6。willgiveaclearideaofthiscontrivance；andtheexperienceIhavehadofithasprovedthatitanswersperfectlywellthepurposeforwhichitisdesigned。
Iobservedabove，thatthenewback，whichitwillalwaysbefoundnecessarytobuildinordertobringthefiresufficientlyforward，inalteringaChimneyconstructedonthecommonprinciples，needneverbethickerthanthewidthofacommonbrick——Imaysaythesameofthethicknessnecessarytobegiventothenewsides，orcovings，oftheChimney；orifthenewbackandcovingsareconstructedofstone，oneinchandthreequarters，ortwoinchesinthicknesswillbesufficient——Careshouldbetakeninbuildingupthesenewwallstounitethebacktothecovingsinasolidmanner。
Whetherthenewbackandcovingsareconstructedofstone，orbuiltofbricks，thespacebetweenthem，andtheoldbackandcovingsoftheChimneyoughttobefilledup，togivegreatersoliditytothestructure——Thismaybedonewithlooserubbish，orpiecesofbrokenbricks，orstonesprovidedtheworkbestrengthenedbyafewlayersorcoursesofbrickslaidinmortar；
butitwillbeindispensablynecessarytofinishthework，wherethesenewwallsend，thatistosay，atthetopofthethroatoftheChimney，whereitendsabruptlyintheopencanaloftheChimneybyahorizontalcourseofbrickswellsecuredwithmortar——
Thiscourseofbrickswillbeuponalevelwiththetopofthedoor-wayleftfortheChimney-sweeper。
FromthesedescriptionsitisclearthatwherethethroatoftheChimneyhasanend，thatistosay，whereitentersintothelowerpartoftheopencanaloftheChimney，THEREthethreewallswhichformthetwocovingsandthebackoftheFire-placeallendabruptly——Itisofmuchimportancethattheyshouldendinthismanner；forweretheytobeslopedoutwardandraisedinsuchamannerastoswellouttheupperextremityofthethroatoftheChimneyintheformofatrumpet，andincreaseitbydegreestothesizeofthecanaloftheChimney，thismannerofunitingthelowerextremityofthecanaloftheChimneywiththethroatwouldtendtoassistthewindswhichmayattempttoblowdowntheChimney，inforcingtheirwaythroughthethroat，andthrowingthesmokebackwardintotheroom；butwhenthethroatoftheChimneyendsabruptly，andtheendsofthenewwallsformaflathorizontalsurface，itwillbemuchmoredifficultforanywindfromabove，tofind，andforceitswaythroughthenarrowpassageofthethroatoftheChimney。
AsthetwowallswhichformthenewcovingsoftheChimneyarenotparalleltoeachother；butinclined，presentinganobliquesurfacetowardsthefrontoftheChimney，andastheyarebuiltperfectlyuprightandquiteflat，fromthehearthtothetopofthethroat，wheretheyend，itisevidentthatanhorizontalsectionofthethroatwillnotbeanoblongsquare；butitsdeviationfromthatformisamatterofnoconsequence；andnoattemptsshouldeverbemade，bytwistingthecovingsabove，wheretheyapproachthebreastoftheChimney，tobringittothatform——Alltwists，bends，prominences，excavations，andotherirregularitiesofform，inthecovingsofaChimney，neverfailtoproduceeddiesinthecurrentofairwhichiscontinuallypassinginto，andthroughanopenFire-placeinwhichafireisburning；——andallsucheddiesdisturb，eitherthefire，ortheascendingcurrentsofsmoke，orboth；andnotunfrequentlycausethesmoketobethrownbackintotheroom——Henceitappears，thatthecovingsofChimneysshouldneverbemadecircular，orintheformofanyothercurve；butalwaysquiteflat。
Forthesamereason，thatistosay，topreventeddies，thebreastoftheChimney，whichformsthatsideofthethroatthatisinfront，ornearesttotheroom，shouldbenearlycleanedoff，anditssurfacemadequiteregularandsmooth。
Thismayeasilybedonebycoveringitwithacoatofplaster，whichmaybemadethickerorthinnerindifferentpartsasmaybenecessaryinordertobringthebreastoftheChimneytobeoftheproperform。
WithregardtotheformofthebreastofaChimney，thisisamatterofverygreatimportance，andwhichoughtalwaystobeparticularlyattendedto——Theworstformitcanhaveisthatofaverticalplane，oruprightflat；——andnexttothistheworstformisaninclinedplane——Boththeseformscausethecurrentofwarmairfromtheroom，whichwill，inspiteofeveryprecaution，sometimesfinditswayintotheChimney，tocrossuponthecurrentofsmoke，whichrisesfromthefire，inamannermostlikelytoembarrassitinitsascent，anddriveitback——
TheinclinedplanewhichisformedbyaflatregisterplacedinthethroatofaChimneyproducesthesameeffects；andthisisonereason，amongmanyothers，whichhaveinducedmetodisapproveofregisterstoves。
Thecurrentofair，which，passingunderthemantle，getsintotheChimney，shouldbemadeGRADUALLYTOBENDITSCOURSEUPWARDS，bywhichmeansitwillbeQUIETLYwiththeascendingcurrentofsmoke，andwillbelesslikelytocheckit，orforceitbackintotheroom——Nowthismaybeeffectedwiththegreatesteaseandcertainty，merelybyROUNDINGOFFthebreastoftheChimneyorbackpartofthemantle，insteadofleavingitflat，orfullofholesandcorners；andthisofcourseoughtalwaystobedone。
Ihavehithertogivennoprecisedirectionsinregardtotheheighttowhichthenewbackandcovingsoughttobecarried：——
Thiswilldependnotonlyontheheightofthemantle，butalso，andmoreespecially，ontheheightofthebreastoftheChimney，orofthatpartoftheChimneywherethebreastendsandtheuprightcanalbegins——Thebackandcovingsmustriseafewinches，fiveorsixforinstance，higherthanthispart，otherwisethethroatoftheChimneywillnotbeproperlyformed：——butIknowofnoadvantagesthatwouldbegainedbycarryingthemupstillhigher。
Imentionedabove，thatthespacebetweenthewallswhichformthenewbackandcovings，andtheoldbackandsidesoftheFire-place，shouldbefilledup：——butthismustnotbeunderstoodtoapplytothespacebetweenthewallofdrybricks，orthetilewhichclosesthepassagefortheChimney-sweeper，andtheoldbackoftheChimney；forthatspacemustbeleftvoid，otherwise，thoughthistilewhichatmostwillnotbemorethantwoinchesinthickness，weretakenaway，therewouldnotbeanyroomsufficientforhimtopass。
Informingthisdoor-way，thebestmethodofproceedingistoplacethetileorflatpieceofstonedestinedforclosingit，initsproperplace；andtobuildroundit，orratherbythesidesofit；takingcarenottobringanymortarnearit，inorderthatitmaybeeasilyremovedwhenthedoor-wayisfinished——Withregardtotherabbetwhichshouldbemadeinthedoor-waytoreceiveitandfixitmorefirmlyinitsplace，thismayeitherbeformedatthesametimewhenthedoor-wayisbuilt，oritmaybemadeafteritisfinished，byattachingtoitsbottomandsides，withstrongmortar，piecesofthinrooftiles。Suchasareabouthalfaninchinthicknesswillbebestforthisuse；
iftheyarethicker，theywilldiminishtoomuchtheopeningofthedoor-way，andwilllikewisebemoreliabletobetornawaybytheChimney-sweeperinpassingupanddowntheChimney。
Itwillhardlybenecessaryformetoadd，thatthetile，orflatstone，orwallofdrybricks，whichisusedforclosingupthedoor-way，mustbeofsufficientheighttoreachquiteuptoalevelwiththetopofthewallswhichformthenewbackandcovingsoftheChimnies。
Iought，perhaps，toapologizeforhavingbeensoveryparticularinthesedescriptionandexplanations，butitmustberememberedthatthischapteriswrittenprincipallyfortheinformationofthosewho，havinghadfewopportunitiesofemployingtheirattentioninabstrusephilosophicalresearches，arenotsufficientlypractisedintheseintricateinvestigations，toseize，withfacility，newideas；——andconsequently，thatIhavefrequentlybeenobligedTOLABOURtomakemyselfunderstood。
IhaveonlytoexpressmywishesthatmyreadermaynotbemoreFATIGUEDwiththislabourthanIhavebeen；——forweshallthemmostcertainlybesatisfiedwitheachother——Buttoreturnoncemoretothecharge。
ThereisoneimportantcircumstancerespectingChimneyFire-places，destinedforburningcoals，whichstillremainstobefartherexamined；——andthatistheGrate。
AlthoughtherearefewgratesthatmaynotbeusedinChimneysconstructedoralteredupontheprincipleshererecommended，yettheyarenot，byanymeans，allequallywelladaptedforthatpurpose——Thosewhoseconstructionisthemostsimple，andwhichofcoursearethecheapest，arebeyondcomparisonthebest，ONALLACCOUNTS——NothingbeingwantedintheseChimniesbutmerelyagrateforcontainingthecoals，andinwhichtheywillburnwithaclearfire；——andalladditionalapparatusbeing，notonlyuseless，butverypernicious，allcomplicatedandexpensivegratesshouldbelaidaside，andsuchasmoresimplesubstitutedintheroomofthem——Andinthechoiceofagrate，asineverythingelse，BEAUTYandELEGANCEmayeasilybeunitedwiththeMOSTPERFECTSIMPLICITY——Indeedtheyareincompatiblewitheverythingelse。
Inplacingthegrate，thethingprincipallytobeattendedtois，tomakethebackofitcoincidewiththebackoftheFire-place；——
butasmanyofthegratesnowincommonusewillbefoundtobetoolarge，whentheFire-placesarealteredandimproved，itwillbenecessarytodiminishtheircapacitiesbyfillingthemupatthebackandthesideswithpiecesoffire-stone。Whenthisisdone，itisthefrontoftheflatpieceoffire-stonewhichismadetoformanewbacktothegrate，whichmustbemadetocoincidewith，andmakepartoftheback，oftheFire-place——
Butindiminishingthecapacitiesofgrateswithpiecesoffire-stone，caremustbetakennottomakethemTOONARROW。
Theproperwidthforgratesdestinedforroomsofamiddlingsizewillbefromsixtoeightinches，andtheirlengthmaybediminishedmoreorless，accordingastheroomisheatedwithmoreorlessdifficulty，orastheweatherismoreorlesssevere——
Butwherethewidthofagrateisnotmorethanfiveinches，itwillbeverydifficulttopreventthefirefromgoingout。
Itgoesoutforthesamereasonthatalivecoalfromthegratethatfallsuponthehearthsoonceasestoberedhot；——itiscooledbythesurroundingcoldairoftheatmosphere——
Theknowledgeofthecausewhichproducesthiseffectisimportant，asitindicatesthemeanswhichmaybeusedforpreventingit——
ButofthissubjectIshalltreatmorefullyhereafter。
Itfrequentlyhappensthattheironbacksofgratesarenotvertical，orupright，butinclinedbackwards——Whenthesegratesaresomuchtoowideastorenderitnecessarytofillthemupbehindwithfire-stone，theinclinationofthebackwillbeoflittleconsequence；forbymakingthepieceofstonewithwhichthewidthofthegrateistobediminishedintheformofawedge，orthickerabovethanbelow，thefrontofthisstone，whichineffectwillbecomethebackofthegrate，maybemadeperfectlyvertical；andtheironbackofthegratebeinghidinthesolidworkofthebackoftheFire-place，willproducenoeffectwhatever；butifthegratebealreadysonarrowasnottoadmitofanydiminutionofitswidth，inthatcaseitwillbebesttotakeawaytheironbackofthegrateentirely，andfixingthegratefirmlyinthebrick-work，causethebackoftheFire-placetoserveasabacktothegrate——ThisIhaveveryfrequentlydone，andhavealwaysfoundittoanswerperfectlywell。
Whereitisnecessarythatthefireinagrateshouldbeverysmall，itwillbebest，inreducingthegratewithfire-stone，tobringitscavity，destinedforcontainingthefuel，totheformofonehalfofahollowhemisphere；thetwosemicircularopeningsbeingoneabove，toreceivethecoals，andtheotherinfront，ortowardsthebarsofthegrate；forwhenthecoalsareburntinsuchaconfinedspace，andsurroundedonallsides，exceptinthefrontandabove，byfire-stone，asubstancepeculiarlywelladaptedforconfiningheat，theheatofthefirewillbeconcentrated，andthecoldairoftheatmospherebeingkeptatadistance，amuchsmallerquantityofcoalswillburn，thancouldpossiblybemadetoburninagratewheretheywouldbemoreexposedtobecooledbythesurroundingair，ortohavetheirheatcarriedoffbybeingincontactwithiron，orwithanyothersubstancethroughwhichheatpasseswithgreaterfacilitythanthroughfire-stone。
BeingpersuadedthatiftheimprovementsinChimneyFire-placeshererecommendedshouldbegenerallyadopted，whichIcannothelpflatteringmyselfwillbethecase，thatitwillbecomenecessarytoreduce，veryconsiderably，thesizesofgrates，Iwasdesirousofshowinghowthismay，withthegreatestsafetyandfacility，bedone。
Wheregrates，whicharedesignedforroomsofamiddlingsize，arelongerthan14or15inches，itwillalwaysbebest，notmerelytodiminishtheirlengths，byfillingthemupattheirtwoendswithfire-stone，but，formingthebackoftheChimneyofaproperwidth，withoutpayinganyregardtothelengthofthegrate，tocarrythecovingsthroughthetwoendsofthegrateinsuchamannerastoconcealthem，oratleasttoconcealthebackcornersoftheminthewallsofthecovings。
IcannothelpflatteringmyselfthatthedirectionsheregiveninregardtothealterationswhichitmaybenecessarytomakeinFire-places，inordertointroducetheimprovementsproposed，willbefoundtobesoperfectlyplainandintelligiblethatnoonewhoreadsthemwillbeatanylossrespectingthemannerinwhichtheworkistobeperformed；——butasorderandarrangementtendmuchtofacilitateallmechanicaloperations，IshallheregiveafewshortdirectionsrespectingthemannerofLAYINGOUT
THEWORK，whichmaybefounduseful，andparticularlytogentlemenwhomayundertaketobetheirownarchitects，inorderinganddirectingthealterationstobemadefortheimprovementoftheirFire-places。
DirectionsforlayingouttheWork。
IftherebeagrateintheChimneywhichistobealtered，itwillalwaysbebesttotakeitaway；andwhenthisisdone，therubbishmustberemoved，andthehearthsweptperfectlyclean。
SupposetheannexedfigureNo。1。torepresentthegroundplanofsuchaFire-place；ABbeingtheopeningofitinfront，ACandBDthetwosidesorcovings，andCDtheback。
Figure2。showstheelevationofthisFire-place。
Firstdrawastraitline，withchalk，orwithaleadpencil，uponthehearth，fromonejambtotheother，——evenwiththefrontofthejambs。ThedottedlineAB，figure3，mayrepresentthisline。
FromthemiddleCofthisline，ABanotherlinecd，istobedrawnperpendiculartoit，acrossthehearth，tothemiddled，ofthebackoftheChimney。
ApersonmustnowstanduprightintheChimney，withhisbacktothebackoftheChimney，andholdaplumb-linetothemiddleoftheupperpartofthebreastoftheChimneyd，fig。5，orwherethecanaloftheChimneybeginstoriseperpendicularly；——
takingcaretoplacethelineaboveinsuchamannerthattheplumbmayfallonthelinecd，drawonthehearthfromthemiddleoftheopeningoftheChimneyinfronttothemiddleoftheback，andanassistantmustmarkthepreciseplacee，onthatlinewheretheplumbfalls。
Thisbeingdone，andthepersonintheChimneyhavingquittedhisstation，fourinchesaretobesetoffthelinecd，frome，towardsd；andthepointf，wherethesefourinchesend，whichmustbemarkedwithchalk，orwithapencil，willshowhowfarthenewbackistobebroughtforward。
Throughf，drawthelinegh，paralleltothelineAB，andthislineghwillshowthedirectionofthenewback，orthegroundlineuponwhichitistobebuilt。
ThelinecfwillshowthedepthofthenewFire-place；andifitshouldhappenthatcfisequaltoaboutONE-THIRDofthelineAB；
andifthegratecanbeaccommodatedtotheFire-placeinsteadofitsbeingnecessarytoaccommodatetheFire-placetothegrate，inthatcase，halfthelengthofthelinecf，istobesetofffromfonthelinegfh，ononesidetok，andontheothertoi，andthelineikwillshowthegroundlineoftheforepartofthebackoftheChimney。
InallcaseswherethewidthoftheopeningoftheFire-placeinfrontABhappenstobenotgreater，ornotmorethantwoorthreeinchesgreaterthanTHREETIMESthewidthofthenewbackoftheChimneyik，thisopeningmaybeleft，andlinesdrawnfromitoA，andfromktoB，willshowthewidthandpositionofthefrontofthenewcovings；——butwhentheopeningoftheFire-placeinfrontisstillwider，itmustbereduced；whichistobedoneinthefollowingmanner：
Fromc，themiddleofthelineAB，caandcb，mustbesetoffequaltothewidthofthebackik，addedtohalfitswidthfi，andlinesdrawnfromitoa，andfromktob，willshowthegroundplanofthefrontsofthenewcovings。
Whenthisisdone，nothingmorewillbenecessarythantobuildupthebackandcovings；andiftheFire-placeisdesignedforburningcoals，tofixthegrateinitsproperplace，accordingtothedirectionsalreadygiven——WhenthewidthoftheFire-placeisreduced，theedgesofthecovingsaAandbBaretomakeafinishwiththefrontofthejambs——Andingeneralitwillbebest，notonlyforthesakeoftheappearanceoftheChimney，butforotherreasonsalso，tolowertheheightoftheopeningoftheFire-place，wheneveritswidthinfrontisdiminished。
Fig。4。showsafrontviewoftheChimneyafterithasbeenalteredaccordingtothedirectionsheregiven——Bycomparingitwithfig。2。whichshowsafrontviewofthesameChimneybeforeitwasaltered，themannerinwhichtheopeningoftheFire-placeinfrontisdiminishedmaybeseen——Infig。4。theunderpartofthedoor-waybywhichtheChimney-sweepergetsuptheChimneyisrepresentedbywhitedottedlines。Thedoor-wayisrepresentedclosed。
Ishallfinishthischapterwithsomegeneralobservationsrelativetothesubjectunderconsideration；withdirectionshowtoproceedwheresuchlocalcircumstancesexistasrendermodificationsofthegeneralplanindispensablynecessary。
WhetheraChimneybedesignedforburningwooduponthehearth，orwood，orcoalsinagrate，theformoftheFire-placeisinmyopinion，mostperfectwhenTHEWIDTHOFTHEBACKisequaltotheDEPTHOFTHEFIRE-PLACE，andtheopeningoftheFire-placeinfrontequaltoTHREETIMESthewidthoftheback，or，whichisthesamething，toTHREETIMESTHEDEPTHOFTHEFIRE-PLACE。
ButiftheChimneybedesignedforburningwooduponthehearth，uponhandirons，ordogs，astheyarecalled，itwillsometimesbenecessarytoaccommodatethewidthofthebacktothelengthofthewood；andwhenthisisthecase，thecovingsmustbeaccommodatedtothewidthoftheback，andtheopeningoftheChimneyinfront。
WhenthewalloftheChimneyinfront，measuredfromtheupperpartofthebreastoftheChimneytothefrontofthemantle，isverythin，itmayhappen，andespeciallyinChimniesdesignedforburningwooduponthehearth，orupondogs，thatthedepthoftheChimney，determinedaccordingtothedirectionsheregiven，maybetoosmall。
Thus，forexample，supposingthewalloftheChimneyinfront，fromtheupperpartofthebreastoftheChimneytothefrontofthemantle，tobeonlyfourinches，whichissometimesthecase，particularlyinroomssituatednearthetopofahouse，inthiscase，ifwetakefourinchesforthewidthofthethroat，thiswillgiveeightinchesonlyforthedepthoftheFire-place，whichwouldbetoolittle，evenwerecoalstobeburntinsteadofwood——InthiscaseIshouldincreasethedepthoftheFire-placeatthehearthto12or13inches，andshouldbuildthebackperpendiculartotheheightofthetopoftheburningfuel，whetheritbewoodburntuponthehearth，orcoalsinagrate，
andthen，slopingthebackbyagentleinclinationforward，bringittoitsproperplace，thatistosay，PERPENDICULARLYUNDERTHE
BACKOFTHETHROATOFTHECHIMNEY。Thisslope，whichwillbringthebackforwardfourorfiveinches，orjustasmuchasthedepthoftheFire-placeisencreased，thoughitoughtnottobetooabrupt，yetitoughttobequitefinishedattheheightofeightorteninchesabovethefire，otherwiseitmayperhapscausetheChimneytosmoke；butwhenitisverynearthefire，theheatofthefirewillenablethecurrentofrisingsmoketoovercometheobstaclewhichthisslopewillopposetoitsascent，whichitcouldnotdosoeasilyweretheslopesituatedatagreaterdistancefromtheburningfuel[2]。
Fig。7，8，and9，showaplan，elevation，andsectionofaFire-placeconstructedoraltereduponthisprincipal——ThewalloftheChimneyinfrontata，fig。9，beingonlyfourinchesthick，fourinchesmoreaddedtoitforthewidthofthethroatwouldhaveleftthedepthoftheFire-placemeasureduponthehearthbconlyeightinches，whichwouldhavebeentoolittle；——anichecande，wasthereforemadeinthenewbackoftheFire-placeforreceivingthegrate，whichnichewassixinchesdeepinthecenterofit，below13incheswide，orequalinwidthtothegrate，and23incheshigh；finishingabovewithasemicirulararch，which，initshighestpart，roseseveninchesabovetheupperpartofthegrate——Thedoor-wayfortheChimney-sweeper，whichbeginsjustabovethetopoftheniche，maybeseendistinctlyinboththefigures8and9——Thespacemarkedg，fig。9，behindthisdoor-way，mayeitherbefilledwithloosebricks，ormaybeleftvoid——Themannerinwhichthepieceofstonef，fig。9，whichisputunderthemantleoftheChimneytoreducetheheightoftheopeningoftheFire-place，isroundedoffontheinsideinordertogiveafairruntothecolumnofsmokeinitsascentthroughthethroatoftheChimney，isclearlyexpressedinthisfigure。
Theplanfig。7，andelevationfig。8，showhowmuchthewidthoftheopeningoftheFire-placeinfrontisdiminished，andhowthecovingsinthenewFire-placeareformed。
AperfectideaoftheformanddimensionoftheFire-placeinitsoriginalstate，asalsoafteritsalteration，maybehadbycarefulinspectionofthesefigures。
Ihaveaddedthedrawingfig。10，merelytoshowhowafault，whichIhavefoundworkmeningeneralwhomIhaveemployedinalteringFire-placesareveryapttocommit，istobeavoided——
InChimneyslikethatrepresentedinthisfigure，wherethejambsAandBprojectfarintotheroom，andwherethefrontedgeofthemarbleslab，owhichformsthecoving，doesnotcomesofarforwardasthefrontofthejambs，theworkmeninconstructingthenewcovingsareveryapttoplacethem，——notinthelinecA，whichtheyoughttodo，——butinthelineco，whichisagreatfault——ThecovingsofaChimneyshouldneverrangeBEHINDthefrontofthejambs，howeverthosejambsmayprojectintotheroom；——butitisnotabsolutelynecessarythatthecovingsshouldMAKEAFINISHwiththeinternalfrontcornersofthejambs，orthattheyshouldbecontinuesfromthebackc，quitetothefrontofthejambsatA——Theymayfinishinfrontataandb，andsmallcornersA，o，a，maybeleftforplacingtheshovels，tongs，etc。
Werethenewcovingtorangewiththefrontedgeoftheoldcovingo，theobliquityofthenewcovingwouldcommonlybetoogreat；——ortheangledcowouldexceed135degrees，WHICHIT
NEVERSHOULDDO，——oratleastneverbymorethanaveryfewdegrees。
NoinconvenienceofanyimportancewillarisefrommakingtheobliquityofthecovingsLESSthanwhatishererecommended；
butmanycannotfailtobeproducedbymakingitmuchgreater；——
andasIknowfromexperiencethatworkmenareveryapttodothis，Ihavethoughtitnecessarytowarnthemparticularlyagainstit。
Fig。11。showshowthewidthandobliquityofthecovingsofaChimneyaretobeaccommodatedtothewidthoftheback，andtotheopeninginfrontanddepthoftheFire-place，wherethewidthoftheopeningoftheFire-placeislessthanthreetimesthewidthofthenewback。AsallthosewhomaybeemployedinalteringChimneysmaynot，perhaps，knownhowtosetoffanangleofanycertainnumbersofdegrees，——ormaynothaveathandtheinstrumentsnecessaryfordoingit，——Ishallhereshowhowaninstrumentmaybemadewhichwillbefoundtobeveryusefulinlayingouttheworkforthebricklayers。
Uponaboardabout18incheswideandfourfeetlong，oruponthefloororatable，drawthreeequalsquaresA，B，C，fig。12。ofabout12or14incheseachside，placedinastraitline，andtouchingeachother——FromthebackcornercofthecentersquareB，drawadiagonallineacrossthesquareA，toitsoutwardfrontcornerf，andtheadjoiningangleformedbythelinesdcandcfwillbeequalto135degrees，——theanglewhichtheplaneofthebackofaChimneyFire-placeoughttomakewiththeplaneofitscovings——Andabevelm，n，beingmadetothisanglewiththinslipsofhardwood，thislittleinstrumentwillbefoundtobeveryusefulinmarkingoutonthehearth，withchalk，theplansofthewallswhicharetoformthecovingsofFire-places。
AsChimneyswhichareapttosmokewillrequirethecovingstobeplacedlessobliquelyinrespecttothebackthanotherswhichhavenotthatdefect，itwouldbeconvenienttobeprovidedwithseveralbevels；——threeorfour，forinstance，formingdifferentangles——Thatalreadydescribed，whichmaybecalledNo。1。willmeasuretheobliquityofthecovingswhentheFire-placecanbemadeofthemostperfectform：——anotherNo。2。maybemadetoasmallerangle，dce，——andanotherNo。3。forChimnieswhichareveryapttosmokeatthestillsmallerangledci——Orabevelmaybesocontrived，bymeansofajoint，andanarch，properlygraduated，astoserveforallthedifferentdegreesofobliquitywhichitmayeverbenecessarytogivetothecovingsofFire-places。
Anotherpointofmuchimportance，andparticularlyinChimneyswhichareapttosmoke，istoformthethroatoftheChimneyproperly，bycarryingupthebackandcovingstoaproperheight。This，workmenareapttoneglecttodo，probablyonaccountofthedifficultytheyfindinworkingwheretheopeningofthecanaloftheChimneyissomuchreduced——ButitisabsolutelynecessarythatthesewallsshouldbecarriedupfiveorsixinchesatleastabovetheupperpartofthebreastoftheChimney，ortothatpointwherethewallwhichformsthefrontofthethroatbeginstoriseperpendicularly——IftheworkmanhasintelligenceenoughtoavailhimselfoftheopeningwhichisformedinthebackoftheFire-placetogiveapassagetotheChimney-sweeper，hewillfindlittledifficultyinfinishinghisworkinapropermanner。
Inplacingtheplumb-lineagainstthebreastoftheChimney，inordertoascertainhowfarthenewbackistobebroughtforward，greatcaremustbetakentoplaceitattheverytopofthebreast，wherethecanaloftheChimneyBEGINSTORISE
PERPENDICULARLY；otherwise，whentheplumb-lineisplacedtoolow，oragainsttheslopeofthebreast，whenthenewbackcomestoberaisedtoitsproperheight，thethroatoftheChimneywillfoundtobetoonarrow。
Sometimes，andindeedveryoftenthetopofthebreastofaChimneyliesveryhigh，orfarabovethefireseethefigures13
and14，wheredshowsthetopofthebreastoftheChimney；
whenthisisthecaseitmustbebroughtlower，otherwisetheChimneywillbeveryapttosmoke——SomuchhasbeensaidintheFirstChapterofthisEssayoftheadvantagestobederivedfrombringingthethroatofaChimneyneartotheburningfuel，thatI
donotthinkitnecessarytoenlargeontheminthisplace，——
takingitforgrantedthattheutilityandnecessityofthatarrangementhavealreadybeenmadesufficientlyevident；——
butafewdirectionsforworkmen，toshowthemhowthebreastandconsequentlythethroatofaChimneycanmostreadilybelowered，maynotbesuperfluous。
WherethetoogreatheightofthebreastofaChimneyisowingtothegreatheightofthemantle，seefig。13，or，whichisthesamething，oftheopeningoftheFire-placeinfront，whichwillcommonlybefoundtobethecase；theonlyremedyfortheevilwillbetobringdownthemantlelower；——orrather，tomaketheopeningoftheFire-placeinfrontlower，bythrowingacrossthetopofthisopening，fromonejambtotheother，andimmediatelyunderthemantle，averyflatarch；——awallofbricksandmortar，supportedonstraightbarsofiron；——orapieceofstoneh，fig。13——Whenthisisdone，theslopeoftheoldthroatoftheChimney，orofthebacksideofthemantle，istobefilledupwithplaster，soastoformonecontinuedflat，vertical，oruprightplanesurfacewiththelowerpartofthewallofthecanaloftheChimney，andanewbreastistobeformedlowerdown，carebeingtakentorounditoffproperly，andmakeitfinishatthelowersurfaceofthenewwallbuiltunderthemantle；——whichwallformsinfactanewmantle。
Theannexeddrawingfig。13，whichrepresentsthesectionofaChimneyinwhichthebreasthasbeenloweredaccordingtothemethodheredescribed，willshowthesevariousalterationsinaclearandsatisfactorymanner。Inthisfigure，aswellasinmostoftheothersinthisEssay，theoldwallsaredistinguishedfromthenewonesbythemannerinwhichtheyareshaded；——
theoldwallsbeingshadedbydiagonallines，andthenewonesbyverticallines。Theadditions，whichareformedofplaster，areshadedbydotsinsteadoflines。
WherethetoogreatheightofthebreastofaChimneyisoccasioned，notbytheheightofthemantle，butbythetoogreatwidthofthebreast，inthatcase，whichhoweverwillseldombefoundtooccur，thisdefectmayberemediedbycoveringthelowerpartofthebreastwithathickcoatingofplaster，supported，ifnecessary，bynailsorstuds，drivenintothewallwhichformsthebreast，andproperlyroundedoffatthelowerpartofthemantle——Seefig。14。
CHAPTER。III。
Ofthecauseoftheascentofsmoke。
Illustrationofthesubjectbyfamiliarcomparisonsandexperiments。
Ofchimnieswhichaffectandcauseeachothertosmoke。
Ofchimnieswhichsmokefromwantofair。
Oftheeddiesofwindwhichsometimesblowdownchimnies，andcausethemtosmoke。
Explanationofthefigures。
ThoughitwasmywishtoavoidallabstrusephilosophicalinvestigationsinthisEssay，yetIfeelthatitisnecessarytosayafewwordsuponasubjectgenerallyconsideredasdifficulttobeexplained，whichistoointimatelyconnectedwiththematterunderconsiderationtobepassedoverinsilence——
AknowledgeofthecauseoftheascentofSmokebeingindispensablynecessarytothosewhoengageintheimprovementofFire-places，orwhoaredesirousofformingjustideasrelativetotheoperationsoffire，andthemanagementofheat，Ishalldevoteafewpagestotheinvestigationofthatcuriousandinterestingsubject——Andasmanyofthosewhomayderiveadvantagefromtheseinquiriesarenotmuchaccustomedtophilosophicaldisquisitions，andwouldnotreadilycomprehendeitherthelanguageorthediagramscommonlyusedbyscientificwriterstoexplainthephaenomenainquestion，Ishalltakepainstoexpressmyselfinthemostfamiliarmanner，andtousesuchcomparisonsforillustrationasmayeasilybeunderstood。
Ifsmallleadenbullets，orlargegooseshot，bemixedwithpeas，andthewholewellshakeninabushel，theshotwillseparatefromthepeas，andwilltakeitsplaceatthebottomofthebushel；forcingbyitsgreaterweightthepeaswhicharelighter，tomoveupwards，contrarytotheirnaturaltendency，andtaketheirplacesabove。
Ifwaterandlinseedoil，whichislighterthanwater，bemixedinavesselbyshakingthemtogether，uponsufferingthismixturetoremainquite，thewaterwilldescendandoccupythebottomofthevessel，andtheoil，beingforcedoutofitsplacebythegreaterpressuredownwardsoftheheavierliquid，willbeobligedtoriseandswimonthesurfaceofthewater。
Ifabottlecontaininglinseedoilbeplungedinwaterwithitsmouthupwards，andopen，theoilwillascentoutofthebottle，andpassingupwardsthroughthemassofwater，inacontinuedstream，willspreaditselfoveritssurface。
Inlikemannerwhentwofluidsofanykind，ofdifferentdensities，comeintocontact，oraremixedwitheachother，thatwhichisthelightestwillbeforcedupwardsbythatwhichistheheaviest。
Andasheatrarefiesallbodies，fluidsaswellassolids，airaswellaswater，ormercury，——itfollowsthattwoportionsofthesamefluid，atdifferenttemperatures，beingbroughtintocontactwitheachother，thatportionwhichisthehottestbeingmorerarefiedorspecificallyLIGHTERthanthatwhichiscolder，mustbeforcedupwardsbythislast——Andthisiswhatalwayshappensinfact。
Whenhotwaterandcoldwateraremixed，thehottestpartofthemixturewillbefoundtobeatthesurfaceabove；——andwhencoldairisadmittedintoawarmedroom，itwillalwaysbefoundtotakeitsplaceatthebottomoftheroom，thewarmerairbeinginpartexpelled，andinpartforcedupwardstothetopoftheroom。
Bothairandwaterbeingtransparentandcolourlessfluids，theirinternalmotionsarenoteasilydiscoveredbythesight，andwhenthesemotionsareveryslow，theymakenoimpressionwhateveronanyofoursenses，consequentlytheycannotbedetectedbyuswithouttheaidofsomemechanicalcontrivance：——
Butwherewehavereasontothinkthatthosemotionsexist，meansshouldbesought，andmayoftenbefound，forrenderingthemperceptible。
Ifabottlecontaininghotwatertingedwithlog-wood，oranyothercolouringdrug，beimmersed，withitsmouthopen，andupwards，intoadeepglassjarfilledwithcoldwater，theascentofthehotwaterfromthebottlethroughthemassofcoldwaterwillbeperfectlyvisiblethroughtheglass——
Nownothingcanbemoreevidentthanthatbothofthesefluidsareforced，orPUSHED，andnotDRAWNupwards——SmokeisfrequentlysaidtobedrawnuptheChimney；——andthataChimneydrawswell，orill；——butthesearecarelessexpressions，andleadtoveryerroneousideasrespectingthecauseoftheascentofSmoke；
andconsequentlytendtopreventtheprogressofimprovementsinthemanagementoffires——Theexperimentjustmentionedwiththecolouredwaterisverystrikingandbeautiful，anditiswellcalculatedtogiveajustideaofthecauseoftheascentofSmoke。Thecoldwaterinthejar，which，inconsequenceofitssuperiorweightordensity，forcestheheatedandrarefiedwaterinthebottletogiveplacetoit，andtomoveupwardsoutofitsway，mayrepresentthecoldairoftheatmosphere，whiletherisingcolumnofcolouredwaterwillrepresentthecolumnofSmokewhichascendsfromafire。
IfSmokerequiredaChimneytoDRAWitupwards，howhappensitthatSmokerisesfromafirewhichismadeintheopenair，wherethereisnoChimney？
Ifatube，openatbothends，andofsuchalengththatitsupperendbebelowthesurfaceofthecoldwaterinthejar，beheldverticallyoverthemouthofthebottlewhichcontainsthehotcolouredwater，thehotwaterwillriseupthroughit，justasmokerisesinaChimney。
Ifthetubebepreviouslyheatedbeforeitisplungedintothecoldwater，theascentofthehotcolouredwaterwillbefacilitatedandaccelerated，inlikemannerasSmokeisknowntorisewithgreaterfacilityinaChimneywhichishot，thaninoneinwhichnofirehasbeenmadeforalongtime——Butinneitherofthesecasescanit，withanypropriety，besaid，thatthehotwaterisDRAWNupthetube——Thehotterthewaterinthebottleis，andthecolderthatinthejar，thegreaterwillbethevelocitywithwhichthehotwaterwillbeforcedupthroughthetube；andthesameholdsoftheascentofhotSmokeinaChimney——Whenthefireisintense，andtheweatherverycold，theascentoftheSmokeisveryrapid；andundersuchcircumstancesChimneysseldomsmoke。
Asthecoldwaterofthejarimmediatelysurroundingthebottlewhichcontainsthehotwater，willbeheatedbythebottlewhiletheotherpartsofthewaterinthejarwillremaincold，thiswatersoheated，becomingspecificallylighterthanthatwhichsurroundsit，willbeforcedupwards；andifitfindsitswayintothetubewillriseupthroughitwiththecolouredhotwater——ThewarmedairofaroomheatedbyanopenChimneyFire-placehasalwaysatendencytorise，ifImayusethatinaccurateexpression，andfindingitswayintotheChimneyfrequentlygoesoffwiththeSmoke。
Whathasbeensaid，will，Iflattermyself，besufficienttoexplainandillustrate，inaclearandsatisfactorymanner，thecauseoftheascentofSmoke；andjustideasuponthatsubjectareabsolutelynecessaryinordertojudge，withcertainty，ofthemeritofanyschemeproposedfortheimprovementofFire-places；ortotakeeffectualmeasures，inallcases，forcuringsmokingChimnies——Forthoughtheperpetualchangesandalterationswhichareproducedbyaccident，whim，andcaprice，dosometimesleadtousefuldiscoveries，yettheprogressofimprovementundersuchguidancemustbeexceedinglyslow，fluctuating，anduncertain。
AstothecausesofthesmokingofChimnies，theyareverynumerous，andvarious；butasageneralideaofthemmaybeacquiredfromwhathasalreadybeensaiduponthatsubjectinvariouspartsofthisEssay，andastheymay，inallcases，averyfewonlyexcepted，becompletelyremediedbymakingthealterationsinFire-placesherepointedout；Idonotthinkitnecessarytoenumeratethemallinthisplace，ortoenterintothoselongdetailsandinvestigationswhichwouldberequiredtoshowtheprecisemannerinwhicheachofthemoperates，eitheralone，orinconjunctionwithothers。
ThereishoweveronecauseofsmokingChimnieswhichIthinkitisnecessarytomentionmoreparticularly——Inmodernbuilthouses，wherethedoorsandwindowsaregenerallymadetoclosewithsuchaccuracythatnocreviceisleftforthepassageoftheairfromwithout，theChimniesinroomsadjoiningtoeachother，orconnectedbyclosepassages，arefrequentlyfoundtoaffecteachother，andthisiseasytobeaccountedfor——WhenthereisafireburninginoneoftheChimnies，astheairnecessarytosupplythecurrentuptheChimneywherethefireburnscannotbehadinsufficientquantitiesfromwithout，throughtheverysmallcrevicesofthedoorsandwindows，theairintheroombecomesrarefied，notbyheat，butbysubtractionofthatportionofairwhichisemployedinkeepingupthefire，orsupportingthecombustionofthefuel，andinconsequenceofthisrarefaction，itselasticityisdiminished，andbeingatlastovercomebythepressureoftheexternalairoftheatmosphere，thisexternalairrushesintotheroombytheonlypassageleftforit，namely，bytheopenChimneyoftheneighbouringroom：——AndtheflowofairintotheFire-place，anduptheChimneywherethefireisburningbeingconstant，thisexpenceofairissuppliedbyacontinuedcurrentdowntheotherChimney。
IfanattemptbemadetolightfiresinbothChimniesatthesametime，itwillbefoundtobeverydifficulttogetthefirestoburn，andtheroomswillbothbefilledwithSmoke。
Oneofthefires，——thatwhichismadeintheChimneywheretheconstructionoftheFire-placeisbestadaptedtofacilitatetheascentoftheSmoke，——orifbothFire-placesareonthesameconstruction，——thatwhichhasthewindmostfavourable，orinwhichthefirehappenstobesoonestkindled，——willovercometheother，andcauseitsSmoketobebeatbackintotheroombythecoldairwhichdescendsthroughtheChimney——ThemostobviousremedyinthiscaseistoprovideforthesupplyoffreshairnecessaryforkeepingupthefiresbyopeningapassagefortheexternalairintotheroombyashorterroadthandownoneoftheChimnies；andwhenthisisdone，bothChimnieswillbefoundtobeeffectuallycured。
ButChimniessocircumstancedmayveryfrequentlybepreventedfromsmokingevenwithoutopeninganynewpassagefortheexternalair，merelybydiminishingthedraught，asitiscalled，uptheChimnies；whichcanbestbedonebyalteringbothFire-placesupontheprinciplesrecommendedandfullyexplainedintheforegoingChaptersofthisEssay。
Shouldthedoorsandwindowsofaroombeclosedwithsomuchnicetyastoleavenocrevicesbywhichasupplyofaircanentersufficientformaintainingthefire，AFTERTHECURRENTOFAIRUP
THECHIMNEYHASBEENDIMINISHEDASMUCHASPOSSIBLEBY
DIMINISHINGTHETHROATOFTHEFIRE-PLACE；inthatcasetherewouldbenootherwayofpreventingtheChimneyfromsmokingbutbyopeningapassagefortheadmissionoffreshairfromwithout；——butthis，Ibelieve，willveryseldombefoundtobethecase。
AcasemorefrequentlytobemetwithiswherecurrentsofairsetdownChimniesinconsequenceofadiminutionandrarefactionoftheairinaroom，occasionedbythedoorsoftheroomopeningintopassagesorcourtswheretheairisrarefiedbytheactionofsomeparticularwinds。Insuchcasestheevilmayberemedied，eitherbycausingthedoorsinquestiontoclosemoreaccurately，——or，whichwillbestillmoreeffectual，bygivingasupplyofairtothepassageorcourtwhichwantsit，bysomeotherway。
WherethetopofaChimneyiscommandedbyhighbuildings，byclifts，orbyhighgrounds，itwillfrequentlyhappen，inwindyweather，thattheeddiesformedintheatmospherebytheseobstacleswillblowdowntheChimney，andbeatdownthesmokeintotheroom——ThisitistruewillbemuchlesslikelytohappenwhenthethroatoftheChimneyiscontractedandproperlyformedthanwhenitisleftquiteopen，andtheFire-placebadlyconstructed；butasitisPOSSIBLEthataChimneymaybesomuchexposedtotheseeddiesinveryhighwindsastobemadetosmokesometimeswhenthewindblowswithviolencefromacertainquarter，itisnecessarytoshowhowtheeffectsofthoseeddiesmaybeprevented。
VariousmechanicalcontrivanceshavebeenimaginedforpreventingthewindfromblowingdownChimnies，andmanyofthemhavebeenfoundtobeuseful；——thereare，however，manyoftheseinventions，which，thoughtheypreventthewindfromblowingdowntheChimney，aresoill-contrivedonotheraccountsastoobstructtheascentoftheSmoke，anddomoreharmthangood。
OfthisdescriptionareallthoseChimney-potswithflathorizontalplatesorroofsplaceduponsupportersjustabovetheopeningofthepot；——andmostofthecapswhichturnwiththewindarenotmuchbetter——Oneofthemostsimplecontrivancesthatcanbemadeuseof，andwhichinmostcaseswillbefoundtoanswerthepurposeintendedaswellorbetterthanmorecomplicatedmachinery，istocoverthetopoftheChimneywithahollowtruncatedpyramidorcone，thediameterofwhichabove，oropeningforthepassageoftheSmoke，isabout10or11inches——
Thispyramid，orcone，foreitherwillanswer，——shouldbeofearthenware，orofcastiron；——itsperpendicularheightmaybeequaltothediameterofitsopeningabove，andthediameterofitsopeningbelowequaltothreetimesitsheight——ItshouldbeplaceduponthetopoftheChimney，anditmaybecontrivedsoastomakeahandsomefinishtothebrick-work——Whereseveralflewscomeoutneareachother，orinthesamestackofChimnies，theformofapyramidwillbebetterthanthatofaconeforthesecovers。
Theintentionofthiscontrivanceis，thatthewindsandeddieswhichstrikeagainsttheobliquesurfaceofthesecoversmaybereflectedupwardsinsteadofblowingdowntheChimney——
Theinventionisbynomeansnew，butithasnothithertobeenoftenputinpractice——AsoftenasIhaveseenittriedithasbeenfoundtobeofuse；Icannotsay，however，thatIwaseverobligedtohaverecoursetoit，ortoanysimilarcontrivance；
andifIforbeartoenlargeuponthesubjectoftheseinventions，itisbecauseIampersuadedthatwhenChimniesareproperlyconstructedINTHENEIGHBOURHOODOFTHEFIRE-PLACElittlemorewillbenecessarytobedoneatthetopoftheChimneythantoleaveitopen。
IcannotconcludethisEssaywithoutagainrecommending，inthestrongestmanner，acarefulattentiontothemanagementoffiresinopenChimnies；fornotonlythequantityofheatproducedonthecombustionoffueldependsmuchonthemannerinwhichthefireismanaged，butevenoftheheatactuallygeneratedaverysmallpartonlywillbesaved，orusefullyemployed，whenthefireismadeinacarelessandslovenlymanner。
Inlightingacoalfiremorewoodshouldbeemployedthaniscommonlyused，andfewercoals；andassoonasthefireburnsbright，andthecoalsarewelllighted，andNOTBEFORE，morecoalsshouldbeaddedtoincreasethefiretoitspropersize[3]。
TheenormouswasteoffuelinLondonmaybeestimatedbythevastdarkcloudwhichcontinuallyhangsoverthisgreatmetropolis，andfrequentlyovershadowsthewholecountry，farandwide；
forthisdensecloudiscertainlycomposedalmostentirelyofUNCONSUMEDCOAL，whichhavingstolenwingsfromtheinnumerablefiresofthisgreatcityhasescapedbytheChimnies，andcontinuestosailaboutintheair，tillhavinglosttheheatwhichgaveitvolatility，itfallsinadryshowerofextremelyfineblackdusttotheground，obscuringtheatmosphereinitsdescent，andfrequentlychangingthebrightestdayintomorethanEgyptiandarkness。
Ineverviewfromadistance，asIcomeintotown，thisblackcloudwhichhangsoverLondon，withoutwishingtobeabletocomputetheimmensenumberofchaldronsofcoalsofwhichitiscomposed；forcouldthisbeascertained，Iampersuadedsostrikingafactwouldawakenthecuriosity，andexcitetheastonishmentofallranksoftheinhabitants；andPERHAPSturntheirmindstoanobjectofeconomytowhichtheyhavehithertopaidlittleattention。
Conclusion。
ThoughthesavingoffuelwhichwillresultfromtheimprovementsintheformsofCHIMNEYFIRE-PLACEShererecommendedwillbeveryconsiderable，yetIhopetobeabletoshowinafutureEssay，thatstillgreatersavingsmaybemade，andmoreimportantadvantagesderivedfromtheintroductionofimprovementsIshallproposeinKITCHENFIRE-PLACES。
IhopelikewisetobeabletoshowinanEssayonCOTTAGEFIRE-PLACES，whichIamnowpreparingforpublication，thatTHREEQUARTERS，atleast，ofthefuelwhichcottagersnowconsumeincookingtheirvictuals，andinwarmingtheirdwellings，maywithgreatease，andwithoutanyexpensiveapparatus，besaved。
ENDOFTHEFOURTHESSAY。
EXPLANATIONOFTHEFIGURES
[IMAGE]
Fig。1。
TheplanofaFire-placeonthecommonconstruction。
AB，theopeningoftheFire-placeinfront。
CD，thebackoftheFire-place。
ACandBD，thecovings。
Seepage341。
[IMAGE]
Fig。2。
Thisfigureshowstheelevation，orfrontviewofaFire-placeonthecommonconstruction。Seepage341。
[IMAGE]
Fig。3。
ThisFigureshowshowtheFire-placerepresentedbytheFig。1，istobealteredinordertoitsbeingimproved。
ABistheopeninginfront，——CD，theback，andACandBD，thecovingsoftheFire-placeinitsoriginalstate。
ab，itsopeninginfront，——ik，itsback，——andaiandbk，itscovingsafterithasbeenaltered，eisapointuponthehearthuponwhichaplumsuspendedfromthemiddleoftheupperpartofthebreastoftheChimneyfalls。Thesituationforthenewbackisascertainedbytakingthelineefequaltofourinches。
Thenewbackandcovingsarerepresentedasbeingbuiltofbricks；——andthespacebetweentheseandtheoldbackandcovingsasbeingfilledupwithrubbish。Seepage342。
[IMAGE]
Fig。4。
ThisFigurerepresentstheelevationorfrontviewoftheFire-placeFig。3。afterithasbeenaltered。Thelowerpartofthedoor-wayleftfortheChimney-sweeperisshowninthisFigurebywhitedottedlines。Seepage344。
[IMAGE]
Fig。5。
ThisFigureshowsthesectionofaChimneyFire-placeandofapartofthecanaloftheChimney，onthecommonconstruction。
abistheopeninginfront；bc，thedepthoftheFire-placeatthehearth；d，thebreastoftheChimney。
de，thethroatoftheChimney，anddf，ge，apartoftheopencanaloftheChimney。
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Fig。6。
ShowsasectionofthesameChimneyafterithasbeenaltered。
klisthenewbackoftheFire-place；li，thetileorstonewhichclosesthedoor-wayfortheChimney-sweeper；di，thethroatoftheChimney，narrowtofourinches；a，themantle，andh，thenewwallmadeunderthemantletodiminishtheheightoftheopeningoftheFire-placeinfront。
N。B。ThesetwoFiguresaresectionsofthesameChimneywhichisrepresentedineachofthefourprecedingFigures。
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Fig。7。
ThisFigurerepresentsthegroundplanofaChimneyFire-placeinwhichthegrateisplacedinaniche，andinwhichtheoriginalwidthABoftheFire-placeisconsiderablydiminished。
abistheopeningoftheFire-placeinfrontafterithasbeenaltered，anddisthebackofthenicheinwhichthegrateisplaced。Seepage347。
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Fig。8。
ShowsafrontviewofthesameFire-placeafterithasbeenaltered；wheremaybeseenthegrate，andthedoor-wayfortheChimney-sweeper。Seepage347。
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Fig。9。
ShowsasectionofthesameFire-place，cdebeingasectionoftheniche，gthedoor-wayfortheChimney-sweeper，closedbyapieceofthefire-stone，andfthenewwallunderthemantlebywhichtheheightoftheopeningoftheFire-placeinfrontisdiminished。Seepage347。
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Fig。10。
ThisFigureshowshowthecovingsaretobeplacedwhenthefrontofthecovingsaandbdonotcomesofarforwardasthefrontoftheopeningoftheFire-place，orthejambsAandB。
Seepage348。
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Fig。11。
ThisFigureshowshowthewidthandobliquityofthecovingsaretobeaccommodatedtothewidthofthebackofaFire-place，incaseswhereitisnecessarytomakethebackverywide。
Seepage349。
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Fig。12。
ThisFigureshowshowaninstrumentcalledabevelmn，usefulinlayingoutthework，inalteringChimneyFire-places，maybeconstructed。Seepage349。
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Fig。13。
Thisshowshow，whenthebreastofaChimneydistoohigh，itmaybebroughtdownbymeansofawallhplacedunderthemantle，andacoatingofplaster，whichinthisFigureisrepresentedbythepartmarkedbydots。Seepage351。
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Fig。14。
ThisshowshowthebreastofaChimneymaybebroughtdownmerelybyacoatingofplaster。Seepage351。
FootnotesforessayIV。
[1]
EvesandSutton，bricklayers，BroadSanctuary，Westminster，havealonealteredabove90Chimnies——TheexperimentwasfirstmadeinLondonatLordPalmerston’shouseinHanover-square；——thentwoChimnieswerealteredinthehouseofSirJohnSinclair，Baronet，PresidentoftheBoardofAgriculture；oneintheroominwhichtheBoardmeets，andtheotherintheSecretary’sroom；whichlastbeingmuchfrequentedbypersonsfromallpartsofGreatBritain，itwashopedthatcircumstanceswouldtendmuchtoexpeditetheintroductionoftheseimprovementsinvariouspartsofthekingdom。SeveralChimnieswerealteredinthehouseofSirJosephBanks，Baronet，K。B。PresidentoftheRoyalSociety。
AfterwardsanumberwerealteredinDevonshire-house；——inthehouseofEarlBesborough，inCavendish-square，andathisseatatRoehampton；——atHolywell-house，nearSt。Alban’s，theseatoftheCountessDowagerSpencer：——atMelbourne-house；——atLadyTempleton’sinPortland-place；——atMrsMontagu’sinPortman-square；——
atLordSudley’s，inDover-street：——attheMarquisofSalisbury’sseatatHatfield，andathishouseintown；——atLordPalmerston’sseatatBroadlands，nearSouthampton，andatseveralgentlemen’shousesinthatneighbourhood；——andagreatmanyothers；butitwouldbetiresometoenumeratethemall；andeventhesearementionedmerelyforthesatisfactionofthosewhomaywishtomakeinquiriesrespectingthesuccessoftheexperiments。
[2]
HavingbeenobligedtocarrybackwardtheFire-placeinthemannerheredescribed，inordertoaccommodateittoaChimneywhosewallsinfrontwereremarkablythin，——IwassurprisedtofinduponlightingthefirethatitappearedtogiveoutmoreheatintotheroomthananyFire-placeIhadeverconstructed——
Thiseffectwasquiteunexpected；butthecauseofitwastooobviousnottobeimmediatelydiscovered——Theflamerisingfromthefirebrokeagainstthepartofthebackwhichslopedforwardoverthefire，andthispartofthebackbeingsoonverymuchheated，andinconsequenceofitsbeingveryhot，andwhenthefireburntbrightitwasfrequentlyquiteredhot，itthrewoffintotheroomagreatdealofradiantheat——ItisnotpossiblethatthisobliquesurfacetheslopeofthebackoftheFire-place
couldhavebeenheatedred-hotMERELYbytheradiantheatprojectedbytheburningfuel，forotherpartsoftheFire-placenearerthefire，andbettersituatedforreceivingradiantheat，wereneverfoundtobesomuchheated；——andhenceitappearsthatthecombinedheatinthecurrentofsmokeandhotvapourwhichrisesfromanopenfireMAYBE，atleastINPART，stoppedinitspassageuptheChimney，changingintoradiantheat，andafterwardsthrownintotheroom——Thisopensupanewandveryinterestingfieldforexperiment，andbidsfairtoleadtoimportantimprovementsintheconstructionofFire-places——I
haveoflatebeenmuchengagedintheseinvestigations，andamnowactuallyemployeddailyinmakingavarietyofexperimentswithgratesandFire-places，upondifferentconstructions，intheroomIinhabitintheRoyalHotelinPallMall；——andMr。HopkinsofGreek-streetSoho，IronmongertohisMajesty，andMrs。Hempel，atherPotteryatChelsea，arebothatworkintheirdifferentlinesofbusiness，undermydirection，intheconstructionofFire-placesuponaprincipleentirelynew，andwhich，Iflattermyself，willbefoundtobenotonlyelegantandconvenient，butveryeconomical——ButasImeansoontopublishaparticularaccountoftheseFire-places，——withdrawingsandampledirectionsforconstructingthem，Ishallnotenlargefartheronthesubjectinthisplace——Itmayhowevernotbeamissjusttomentionhere，thatthesenew-inventedFire-placesnotbeingfixedtothewallsoftheChimney，butmerelysetdownuponthehearth，maybeusedinanyopenChimney：andthatChimniesalteredorconstructedontheprincipleshererecommendedareparticularlywelladaptedforreceivingthem。
ThePublicingeneral，andmoreparticularlythoseTradesmenandManufacturerswhomitmayconcern，arerequestedtoobserve，thatastheAuthordoesnotintenttotakeouthimself，ortosufferotherstotakeout，anypatentforanyinventionofhiswhichmaybeofpublicutility，allpersonsareatfulllibertytoimitatethem，andvendthem，fortheirownemolument，whenandwhere，andinanywaytheymaythinkproper；andthosewhomaywishforanyfurtherinformationrespectinganyofthoseinventionsorimprovementswillreceivegratisalltheinformationtheycanrequirebyapplyingtotheAuthor，whowilltakepleasureingivingthemeveryassistanceinhispower。
[3]
Kindlingballscomposedofequalpartsofcoal，——charcoal，——andclay，thetwoformerreducedtoafinepowder，wellmixedandkneadedtogetherwiththeclaymoistenedwithwater，andthenformedintoballsofthesizeofhenseggs，andthoroughlydried，mightbeusedwithgreatadvantageinsteadofwoodforkindlingfires。Thesekindlingballsmaybemadesoinflammableastotakefireinaninstantandwiththesmallestspark，bydippingtheminastrongsolutionofnitreandthendryingthemagain，andtheywouldneitherbeexpensivenorliabletobespoiledbylongkeeping。Perhapsaquantityofpurecharcoalreducedtoaveryfinepowderandmixedwiththesolutionofnitreinwhichtheyaredippedwouldrenderthemstillmoreinflammable。
IhaveoftenwonderedthatnoattemptsshouldhavebeenmadetoimprovethefireswhicharemadeintheopenChimniesofelegantapartments，bypreparingthefuel；fornothingsurelywasevermoredirty，inelegant，anddisgustingthanacommoncoalfire。
Fireballsofthesizeofgooseeggs，composedofcoalandcharcoalinpowder，mixedupwithadueproportionofwetclay，andwelldried，wouldmakeamuchmorecleanly，andinallrespectsapleasanterfirethancanbemadewithcrudecoals；
andIbelievewouldnotbemoreexpensivefuel。InFlandersandinseveralpartsofGermany，andparticularintheDutchiesofJuliersandBergen，wherecoalsareusedasfuel，thecoalsarealwayspreparedbeforetheyareused，bypoundingthemtoapowder，andmixingthemupwithanequalweightofclay，andsufficientquantityofwatertoformthewholeintoamasswhichiskneadedtogetherandformedintocakes；whichcakesareafterwardswelldriedandkeptinadryplaceforuse。
Andithasbeenfoundbylongexperiencethattheexpenseattendingthispreparationisamplyrepaidbytheimprovementofthefuel。Thecoals，thusmixedwiththeclay，notonlyburnlonger，butgivemuchmoreheatthanwhentheyareburntintheircrudestate。
Itwilldoubtlessappearextraordinarytothosewhohavenotconsideredthesubjectwithsomeattention，thatthequantityofheatproducedinthecombustionofanyquantityofcoalsshouldbeincreasedbymixingthecoalswithclay，whichiscertainlyanincombustiblebody；——butthephenomenonmay，Ithink，beexplainedinasatisfactorymanner。
Theheatgeneratedinthecombustionofanysmallparticleofcoalexistingundertwodistinctforms，namely，inthatwhichisCOMBINEDwiththeflameandsmokewhichrisefromthefire，andwhichifmeansarenotfoundtostopit，goesoffimmediatelybytheChimneyandislost，——andtheRADIANTHEATwhichissentofffromthefire，inalldirectionsinrightlines：——Ithinkitreasonabletoconclude，thattheparticlesofclaywhicharesurroundedonallsidesbytheflamearrestapartatleastofthecombinedheat，andpreventitsescape；andthiscombinedheat，soarrested，heatingtheclayredhot，isretainedinit，andbeingchangedbythisoperationtoradiantheat，isafterwardsemitted，andmaybedirected，andemployedtousefulpurposes。
Incomposingfireballs，Ithinkitprobablethatacertainproportionofchaff——ofstrawcutveryfine，orevensawdust，mightbeemployedwithgreatadvantage。Iwishthosewhohaveleisurewouldturntheirthoughtstothissubject，forIampersuadedthatveryimportantimprovementswouldresultfromathoroughinvestigationofit。