obtained in the Comhuftion of Fuel. ' 4$ 



are incombustible, as well as thofe which are combuttible, 

 and actually burning, — throw oft, in all directions, heat, or 

 rather calorific (heat-making) rays, which generate heat 

 wherever they are Hopped or abforbcd : but common obfcrv- 

 ation was hardly iufficient to (how any perceptible difference 

 between the quantities of calorific rays thrown off by different 

 bodies, when heated to the fame temperature, or expofed in 

 the fame fire; although the quantities fo thrown off might 

 be, and probably are, very different. 



It has lately been afcertained, that when the fides and 

 back of an open chimney fire-place, in which coals are 

 burned, are compofcd of fire-bricks, and heated red-hot, 

 they throw off into the room incomparably more heat than 

 all the coals that could pofiibly be put into the grate, even 

 fuppofing them to burn with the greateft pofrible degree of 

 brightnefs. Hence it appears that a red-hot burning coal 

 does not fend off near fo many calorific rays as a piece of red- 

 hot brick or Hone, of the lame form and dimensions ; and 

 this interesting difcovery will enable us to make very import- 

 ant improvements in the construction of our fire-places, and 

 alio in the management of our fires. 



The fuel, iniiead of being employed to heat the room di- 

 rectly, or by the direcl rays from the fire, mould be fo dif- 

 pofed or placed as to heat the back and fides of the grate ; 

 which mult always be constructed of fire-brick or fire-Stone, 

 and never of iron or of any other metal. Few coals, there- 

 fore, when properly placed, make a much better fire than a 

 larger quantity; and Shallow grates, when they are conftrutted 

 of proper materials, throw more heat into a room, and with 

 a much lefs confumption of fuel, than deep grates ; for a large 

 mafs of coals in the grate arre(ts-the rays which proceed from 

 the back and fides of the grate, and prevents their coming 

 into the room ; or, as fires are generally managed, it prevents 

 the back and Sides of the grate from ever being fufficiently 

 heated to affift much in heating the room, even though they 

 be constructed of good materials, and large quantities of coals 

 be confumed in them. 



It is pofllble, however, by a Simple contrivance, to make 

 a good and an ceeonomical fire in almoft any grate, though 

 jt would always be advifable to continuSt fire-places on good 

 principles, or to improve them by judicious alterations, rather 

 than to depend on the ufeof additional inventions for corre&T 

 ing their defects. 



To make a good fire in a bad grate, the bottom of the 

 grate muft be firlt covered with a tingle layer of balls, made 

 of good fire-bricks or artificial fire-lione, well burnt, each 



ball 



