Where　the　top　of　a　Chimney　is　commanded　by　high　buildings；　by　clifts；　or　by　high　grounds；　it　will　frequently　happen；　in　windy　weather；　that　the　eddies　formed　in　the　atmosphere　by　these　obstacles　will　blow　down　the　Chimney；　and　beat　down　the　smoke　into　the　room。This　it　is　true　will　be　much　less　likely　to　happen　when　the　throat　of　the　Chimney　is　contracted　and　properly　formed　than　when　it　is　left　quite　open；　and　the　Fire…place　badly　constructed；　but　as　it　is　POSSIBLE　that　a　Chimney　may　be　so　much　exposed　to　these　eddies　in　very　high　winds　as　to　be　made　to　smoke　sometimes　when　the　wind　blows　with　violence　from　a　certain　quarter；　it　is　necessary　to　show　how　the　effects　of　those　eddies　may　be　prevented。
  Various　mechanical　contrivances　have　been　imagined　for　preventing　the　wind　from　blowing　down　Chimnies；　and　many　of　them　have　been　found　to　be　useful；there　are；　however；　many　of　these　inventions；　which；　though　they　prevent　the　wind　from　blowing　down　the　Chimney；　are　so　ill…contrived　on　other　accounts　as　to　obstruct　the　ascent　of　the　Smoke；　and　do　more　harm　than　good。
  Of　this　description　are　all　those　Chimney…pots　with　flat　horizontal　plates　or　roofs　placed　upon　supporters　just　above　the　opening　of　the　pot；and　most　of　the　caps　which　turn　with　the　wind　are　not　much　better。One　of　the　most　simple　contrivances　that　can　be　made　use　of；　and　which　in　most　cases　will　be　found　to　answer　the　purpose　intended　as　well　or　better　than　more　complicated　machinery；　is　to　cover　the　top　of　the　Chimney　with　a　hollow　truncated　pyramid　or　cone；　the　diameter　of　which　above；　or　opening　for　the　passage　of　the　Smoke；　is　about　10　or　11　inches。　This　pyramid；　or　cone；　（for　either　will　answer；）should　be　of　earthen　ware；　or　of　cast　iron；its　perpendicular　height　may　be　equal　to　the　diameter　of　its　opening　above；　and　the　diameter　of　its　opening　below　equal　to　three　times　its　height。It　should　be　placed　upon　the　top　of　the　Chimney；　and　it　may　be　contrived　so　as　to　make　a　handsome　finish　to　the　brick…work。Where　several　flews　come　out　near　each　other；　or　in　the　same　stack　of　Chimnies；　the　form　of　a　pyramid　will　be　better　than　that　of　a　cone　for　these　covers。
  The　intention　of　this　contrivance　is；　that　the　winds　and　eddies　which　strike　against　the　oblique　surface　of　these　covers　may　be　reflected　upwards　instead　of　blowing　down　the　Chimney。　The　invention　is　by　no　means　new；　but　it　has　not　hitherto　been　often　put　in　practice。As　often　as　I　have　seen　it　tried　it　has　been　found　to　be　of　use；　I　cannot　say；　however；　that　I　was　ever　obliged　to　have　recourse　to　it；　or　to　any　similar　contrivance；　and　if　I　forbear　to　enlarge　upon　the　subject　of　these　inventions；　it　is　because　I　am　persuaded　that　when　Chimnies　are　properly　constructed　IN　THE　NEIGHBOURHOOD　OF　THE　FIRE…PLACE　little　more　will　be　necessary　to　be　done　at　the　top　of　the　Chimney　than　to　leave　it　open。
  I　cannot　conclude　this　Essay　without　again　recommending；　in　the　strongest　manner；　a　careful　attention　to　the　management　of　fires　in　open　Chimnies；　for　not　only　the　quantity　of　heat　produced　on　the　combustion　of　fuel　depends　much　on　the　manner　in　which　the　fire　is　managed；　but　even　of　the　heat　actually　generated　a　very　small　part　only　will　be　saved；　or　usefully　employed；　when　the　fire　is　made　in　a　careless　and　slovenly　manner。
  In　lighting　a　coal　fire　more　wood　should　be　employed　than　is　commonly　used；　and　fewer　coals；　and　as　soon　as　the　fire　burns　bright；　and　the　coals　are　well　lighted；　and　NOT　BEFORE；　more　coals　should　be　added　to　increase　the　fire　to　its　proper　size＇3＇。
  The　enormous　waste　of　fuel　in　London　may　be　estimated　by　the　vast　dark　cloud　which　continually　hangs　over　this　great　metropolis；　and　frequently　overshadows　the　whole　country；　far　and　wide；　for　this　dense　cloud　is　certainly　composed　almost　entirely　of　UNCONSUMED　COAL；　which　having　stolen　wings　from　the　innumerable　fires　of　this　great　city　has　escaped　by　the　Chimnies；　and　continues　to　sail　about　in　the　air；　till　having　lost　the　heat　which　gave　it　volatility；　it　falls　in　a　dry　shower　of　extremely　fine　black　dust　to　the　ground；　obscuring　the　atmosphere　in　its　descent；　and　frequently　changing　the　brightest　day　into　more　than　Egyptian　darkness。
  I　never　view　from　a　distance；　as　I　come　into　town；　this　black　cloud　which　hangs　over　London；　without　wishing　to　be　able　to　compute　the　immense　number　of　chaldrons　of　coals　of　which　it　is　composed；　for　could　this　be　ascertained；　I　am　persuaded　so　striking　a　fact　would　awaken　the　curiosity；　and　excite　the　astonishment　of　all　ranks　of　the　inhabitants；　and　PERHAPS　turn　their　minds　to　an　object　of　economy　to　which　they　have　hitherto　paid　little　attention。
  Conclusion。
  Though　the　saving　of　fuel　which　will　result　from　the　improvements　in　the　forms　of　CHIMNEY　FIRE…PLACES　here　recommended　will　be　very　considerable；　yet　I　hope　to　be　able　to　show　in　a　future　Essay；　that　still　greater　savings　may　be　made；　and　more　important　advantages　derived　from　the　introduction　of　improvements　I　shall　propose　in　KITCHEN　FIRE…PLACES。
  I　hope　likewise　to　be　able　to　show　in　an　Essay　on　COTTAGE　FIRE…PLACES；　which　I　am　now　preparing　for　publication；　that　THREE　QUARTERS；　at　least；　of　the　fuel　which　cottagers　now　consume　in　cooking　their　victuals；　and　in　warming　their　dwellings；　may　with　great　ease；　and　without　any　expensive　apparatus；　be　saved。
  END　OF　THE　FOURTH　ESSAY。
  EXPLANATION　OF　THE　FIGURES
  ＇　IMAGE　＇
  Fig。　1。　The　plan　of　a　Fire…place　on　the　common　construction。　A　B；　the　opening　of　the　Fire…place　in　front。　C　D；　the　back　of　the　Fire…place。　A　C　and　B　D；　the　covings。　See　page　341。
  ＇　IMAGE　＇
  Fig。　2。　This　figure　shows　the　elevation；　or　front　view　of　a　Fire…place　on　the　common　construction。　See　page　341。
  ＇　IMAGE　＇
  Fig。　3。　This　Figure　shows　how　the　Fire…place　represented　by　the　Fig。　1；　is　to　be　altered　in　order　to　its　being　improved。
  A　B　is　the　opening　in　front；C　D；　the　back；　and　A　C　and　B　D；　the　covings　of　the　Fire…place　in　its　original　state。
  a　b；　its　opening　in　front；i　k；　its　back；and　a　i　and　b　k；　its　covings　after　it　has　been　altered；　e　is　a　point　upon　the　hearth　upon　which　a　plum　suspended　from　the　middle　of　the　upper　part　of　the　breast　of　the　Chimney　falls。　　The　situation　for　the　new　back　is　ascertained　by　taking　the　line　e　f　equal　to　four　inches。　The　new　back　and　covings　are　represented　as　being　built　of　bricks；and　the　space　between　these　and　the　old　back　and　covings　as　being　filled　up　with　rubbish。　　See　page　342。
  ＇　IMAGE　＇
  Fig。　4。　This　Figure　represents　the　elevation　or　front　view　of　the　Fire…place　Fig。　3。　after　it　has　been　altered。　　The　lower　part　of　the　door…way　left　for　the　Chimney…sweeper　is　shown　in　this　Figure　by　white　dotted　lines。　　See　page　344。
  ＇　IMAGE　＇
  Fig。　5。　This　Figure　shows　the　section　of　a　Chimney　Fire…place　and　of　a　part　of　the　canal　of　the　Chimney；　on　the　common　construction。
  a　b　is　the　opening　in　front；　b　c；　the　depth　of　the　Fire…place　at　the　hearth；　d；　the　breast　of　the　Chimney。
  d　e；　the　throat　of　the　Chimney；　and　d　f；　g　e；　a　part　of　the　open　canal　of　the　Chimney。
  ＇　IMAGE　＇
  Fig。　6。　Shows　a　section　of　the　same　Chimney　after　it　has　been　altered。
  k　l　is　the　new　back　of　the　Fire…place；　l　i；　the　tile　or　stone　which　closes　the　door…way　for　the　Chimney…sweeper；　d　i；　the　throat　of　the　Chimney；　narrow　to　four　inches；　a；　the　mantle；　and　h；　the　new　wall　made　under　the　mantle　to　diminish　the　height　of　the　opening　of　the　Fire…place　in　front。
  N。B。　These　two　Figures　are　sections　of　the　same　Chimney　which　is　represented　in　each　of　the　four　preceding　Figures。
  ＇　IMAGE　＇
  Fig。　7。
  This　Figure　represents　the　ground　plan　of　a　Chimney　Fire…place　in　which　the　grate　is　placed　in　a　niche；　and　in　which　the　original　width　A　B　of　the　Fire…place　is　considerably　diminished。
  a　b　is　the　opening　of　the　Fire…place　in　front　after　it　has　been　altered；　and　d　is　the　back　of　the　niche　in　which　the　grate　is　placed。　See　page　347。
  ＇　IMAGE　＇
  Fig。　8。　Shows　a　front　view　of　the　same　Fire…place　after　it　has　been　altered；　where　may　be　seen　the　grate；　and　the　door…way　for　the　Chimney…sweeper。　See　page　347。
  ＇　IMAGE　＇
  Fig。　9。　Shows　a　section　of　the　same　Fire…place；　c　d　e　being　a　section　of　the　niche；　g　the　door…way　for　the　Chimney…sweeper；　closed　by　a　piece　of　the　fire…stone；　and　f　the　new　wall　under　the　mantle　by　which　the　height　of　the　opening　of　the　Fire…place　in　front　is　diminished。　See　page　347。
  ＇　IMAGE　＇
  Fig。　10。　This　Figure　shows　how　the　covings　are　to　be　placed　when　the　front　of　the　covings　（a　and　b）　do　not　come　so　far　forward　as　the　front　of　the　opening　of　the　Fire…place；　or　the　jambs　（A　and　B）。　See　page　348。
  ＇　IMAGE　＇
  Fig。　11。　This　Figure　shows　how　the　width　and　obliquity　of　the　covings　are　to　be　accommodated　to　the　width　of　the　back　of　a　Fire…place；　in　cases　where　it　is　necessary　to　make　the　back　very　wide。　See　page　349。
  ＇　IMAGE　＇
  Fig。　12。　This　Figure　shows　how　an　instrument　called　a　bevel　（m　n）；　useful　in　laying　out　the　work；　in　altering　Chimney　Fire…places；　may　be　constructed。　See　page　349。
  ＇　IMAGE　＇
  Fig。　13。　This　shows　how；　when　the　breast　of　a　Chimney　（d）　is　too　high；　it　may　be　brought　down　by　means　of　a　wall　（h）　placed　under　the　mantle；　and　a　coating　of　plaster；　which　in　this　Figure　is　represented　by　the　part　marked　by　dots。