o　make　it　appear　in　a　manner　perfectly　satisfactory　to　my　readers　that　I　have　not　ventured　to　give　this　opinion　but　upon　good　and　sufficient　grounds。
  Those　who　will　take　the　trouble　to　consider　the　nature　and　properties　of　elastic　fluids；of　air；smoke；and　vapour；　and　to　examine　the　laws　of　their　motions；　and　the　necessary　consequences　of　their　being　rarified　by　heat；　will　perceive　that　it　would　be　as　much　a　miracle　if　smoke　should　not　rise　in　a　Chimney；　（all　hindrances　to　its　ascent　being　removed；）　as　that　water　should　refuse　to　run　in　a　syphon；　or　to　descend　in　a　river。
  The　whole　mystery；　therefore；　of　curing　smoking　Chimnies　is　comprised　in　this　simple　direction。　　FIND　OUT　AND　REMOVE　THOSE　LOCAL　HINDRANCES　WHICH　FORCIBLY　PREVENT　THE　SMOKE　FROM　FOLLOWING　ITS　NATURAL　TENDENCY　TO　GO　UP　THE　CHIMNEY；　or　rather；　to　speak　more　accurately；　which　prevents　its　being　forced　up　the　Chimney　by　the　pressure　of　the　heavier　air　of　the　room。
  Although　the　causes；　by　which　the　ascent　of　smoke　in　a　Chimney　MAY　BE　obstructed；　are　various；　yet　that　cause　which　will　most　commonly；　and　I　may　say　almost　universally　be　found　to　operate；　is　one　which　it　is　always　very　easy　to　discover；　and　as　easy　to　remove；the　bad　construction　of　the　Chimney　IN　THE　NEIGHBOURHOOD　OF　THE　FIRE…PLACE。
  In　the　course　all　my　experience　and　practice　in　curing　smoking　Chimnies；and　I　certainly　have　not　had　less　than　five　hundred　under　my　hands；　and　among　them　many　which　were　thought　to　be　quite　incurable；I　have　never　been　obliged；　except　in　one　single　instance；　to　have　recourse　to　any　other　method　of　cure　than　merely　reducing　the　Fire…place　and　the　throat　of　the　Chimney；　or　that　part　of　it　which　lies　immediately　above　the　Fire…place；　to　a　proper　form；　and　just　dimensions。
  That　my　principles　for　constructing　Fire…places　are　equally　applicable　to　those　which　are　designed　for　burning　coal；　as　to　those　in　which　wood　is　burnt；　has　lately　been　abundantly　proved　by　experiments　made　here　in　London；　for　of　above　an　hundred　and　fifty　Fire…places　which　have　been　altered　in　this　city；　under　my　direction；　within　these　last　two　months；　there　is　not　one　which　has　not　answered　perfectly　well＇1＇。And　by　several　experiments　which　have　been　made　with　great　care；　and　with　the　assistance　of　thermometers；　it　has　been　demonstrated；　that　the　saving　of　fuel；　arising　from　these　improvements　of　Fire…places；　amounts　in　all　cases　to　more　than　HALF；　and　in　many　cases　to　more　than　TWO　THIRDS　of　the　quantity　formerly　consumed。Now　as　the　alterations　in　Fire…places　which　are　necessary　may　be　made　at　a　very　trifling　expence；　as　any　kind　of　grate　or　stove　may　be　made　use　of；　and　as　no　iron　work；　but　merely　a　few　bricks　and　some　mortar；　or　a　few　small　pieces　of　fire…stone；　are　required；　the　improvement　in　question　is　very　important；　when　considered　merely　with　a　view　to　economy；　but　it　should　be　remembered；　that　not　only　a　great　saving　is　made　of　fuel　by　the　alterations　proposed；　but　that　rooms　are　made　much　more　comfortable；　and　more　salubrious；　that　they　may　be　more　equally　warmed；　and　more　easily　kept　at　any　required　temperature；that　all　draughts　of　cold　air　from　the　doors　and　windows　towards　the　Fire…place；　which　are　so　fatal　to　delicate　constitutions；　will　be　completely　prevented；that　in　consequence　of　the　air　being　equally　warm　all　over　the　room；　or　in　all　parts　of　it；　it　may　be　entirely　changed　with　the　greatest　facility；　and　the　room　completely　ventilated；　when　this　air　is　become　unfit　for　respiration；　and　this　merely　by　throwing　open　for　a　moment　a　door　opening　into　some　passage　from　whence　fresh　air　may　be　had；　and　the　upper　part　of　a　window；　or　by　opening　the　upper　part　of　on　window　and　the　lower　part　of　another；　and　as　the　operation　of　ventilating　the　room；　even　when　it　is　done　in　the　most　complete　manner；　will　never　require　the　door　and　window　to　be　open　more　than　one　minute；　in　this　short　time　the　walls　of　the　room　will　not　be　sensibly　cooled；　and　the　fresh　air　which　comes　into　the　room　will；　in　a　very　few　minutes；　be　so　completely　warmed　by　these　walls　that　the　temperature　of　the　room；　though　the　air　in　it　be　perfectly　changed；　will　be　brought　to　be　very　nearly　the　same　as　it　was　before　the　ventilation。
  Those　who　are　acquainted　with　the　principles　of　pneumatics；　and　know　why　the　warm　air　in　a　room　rushes　out　at　an　opening　made　for　it　at　the　top　of　a　window　when　colder　air　from　without　is　permitted　to　enter　by　the　door；　or　by　any　other　opening　situated　lower　than　the　first；　will　see；　that　it　would　be　quite　impossible　to　ventilate　a　room　in　the　complete　and　expeditious　manner　here　described；　where　the　air　in　a　room　is　partially　warmed；　or　hardly　warmed　at　all；　and　where　the　walls　of　the　room；　remote　from　the　fire；　are　constantly　cold；　which　must　always　be　the　case　where；　in　consequence　of　a　strong　current　up　the　Chimney；　streams　of　cold　air　are　continually　coming　in　through　all　the　crevices　of　the　doors　and　windows；　and　flowing　into　the　Fire…place。
  But　although　rooms；　furnished　with　Fire…places　constructed　upon　the　principles　here　recommended；　may　be　easily　and　most　effectually　ventilated；　（and　this　is　certainly　a　circumstance　in　favour　of　the　proposed　improvements；）　yet　such　total　ventilations　will　very　seldom；　if　ever；　be　necessary。As　long　as　ANY　FIRE　is　kept　up　in　the　room；　there　is　so　considerable　a　current　of　air　up　the　Chimney；　notwithstanding　all　the　reduction　that　can　be　made　in　the　size　of　its　throat；　that　the　continual　change　of　air　in　the　room　which　this　current　occasions　will；　generally；　be　found　to　be　quite　sufficient　for　keeping　the　air　in　the　room　sweet　and　wholesome；　and　indeed　in　rooms　in　which　there　is　no　open　Fire…place；　and　consequently　no　current　of　air　from　the　room　setting　up　the　Chimney；　which　is　the　case　in　Germany；　and　all　the　northern　parts　of　Europe；　where　rooms　are　heated　by　stoves；　whose　Fire…places　opening　without　are　not　supplied　with　the　air　necessary　for　the　combustion　of　the　fuel　from　the　room；and　although　in　most　of　the　rooms　abroad；　which　are　so　heated；　the　windows　and　doors　are　double；　and　both　are　closed　in　the　most　exact　manner　possible；　by　slips　of　paper　pasted　over　the　crevices；　or　by　slips　of　list　or　furr；　yet　when　these　rooms　are　tolerably　large；　and　when　they　are　not　very　much　crowded　by　company；　nor　filled　with　a　great　many　burning　lamps　or　candles；　the　air　in　them　is　seldom　so　much　injured　as　to　become　oppressive　or　unwholesome；　and　those　who　inhabit　them　show　by　their　ruddy　countenances；　as　well　as　by　every　other　sign　of　perfect　health；　that　they　suffer　no　inconvenience　whatever　from　their　closeness。There　is　frequently；　it　is　true；　an　oppressiveness　in　the　air　of　a　room　heated　by　a　German　stove；　of　which　those　who　are　not　much　accustomed　to　living　in　those　rooms　seldom　fail　to　complain；　and　indeed　with　much　reason；　but　this　oppressiveness　does　not　arise　from　the　air　of　the　room　being　injured　by　the　respiration　and　perspiration　of　those　who　inhabit　it；it　arises　from　a　very　different　cause；　from　a　fault　in　the　construction　of　German　stoves　in　general；　but　which　may　be　easily　and　most　completely　remedied；　as　I　shall　show　more　fully　in　another　place。　　In　the　mean　time；　I　would　just　observe　here　with　regard　to　these　stoves；　that　as　they　are　often　made　of　iron；　and　as　this　metal　is　a　very　good　conductor　of　heat；　some　part　of　the　stove　in　contact　with　the　air　of　the　room　becomes　so　hot　as　to　calcine　or　rather　to　ROAST　the　dust　which　lights　upon　it；　which　never　can　fail　to　produce　a　very　disagreeable　effect　on　the　air　of　the　room。　　And　even　when　the　stove　is　constructed　of　pantiles　or　pottery…ware；　if　any　part　of　it　in　contact　with　the　air　of　the　room　is　suffered　to　become　very　hot；　which　seldom　fails　to　be　the　case　in　German　stoves　constructed　on　the　common　principles；　nearly　the　same　effects　will　be　found　to　be　produced　on　the　air　as　when　the　stove　is　made　of　iron；　as　I　have　very　frequently　had　occasion　to　observe。
  Though　a　room　be　closed　in　the　most　perfect　manner　possible；　yet；　as　the　quantity　of　air　injured　and　rendered　unfit　for　further　use　by　the　respiration　of　two　or　three　persons　in　a　few　hours　is　very　small；　compared　to　the　immense　volume　of　air　which　a　room　of　a　moderate　size　contains；　and　as　a　large　quantity　of　fresh　air　always　enters　the　room；　and　an　equal　quantity　of　the　warm　air　of　the　room　is　driven　out　of　it　every　time　the　door　is　opened；　there　is　much　less　danger　of　the　air　of　a　room　becoming　unwholesome　for　the　want　of　ventilation　than　has　been　generally　imagined；　particularly　in　cold　weather；　when　all　the　different　causes　which　conspire　to　change　the　air　of　warmed　rooms　act　with　increased　power　and　effect。
  Those　who　have　any　doubts　respecting　the　very　great　change　of　air　or　ventilation　which　takes　place　each　time　the　door　of　a　warm　room　is　opened　in　cold　weather；　need　only　set　the　door　of　such　a　room　wide　open　for　a　moment；　and　hold　two　lighted　candles　in　the　door…way；　one　near　the　top　of　the　door；　and　the　other　near　the　bottom　of　it；　the　violence　with　which　the　flame　of　that　above　will　be　driven　outwards；　and　that　below　inwards；　by　the　two　strong　currents　of　air　which；　passing　in　opposite　directions；　rush　in　and　out　of　the　room　at　the　same　time；　will　be　convinced　that　the　change　of　air　which　actually　takes　place　must　be　very　co