348 Mr. T. Pridgin Teale [Feb. 5, 



It was clear, therefore, tliat the inclination might be made more 

 acute. Guided by this idea, and having determined the principle on 

 which the shape of the grate should depend, an inclination was 

 arrived at which turned out to be an angle of 60^, i. e. the inclination 

 of the sides of an equilateral triangle. 



Count Rumford came very nearly to the same conclusions : — " I 

 have said, in my essay on chimney fireplaces, that where chimneys 

 are well constructed and well situated, and have never been apt to 

 smoke, in altering them the ' covings ' may be placed at an angle of 

 135 degrees with the back ; but I have expressly said that they should 

 never exceed that angle, and have stated at large the bad consequences 

 that must follow from making the opening of a fireplace very wide, 

 when its depth is very shallow." (V. p. 610.) 



Rule VI. " The ' lean-over ' at the hack should he at an angle 

 of 70° " (Fig. 1). — Commencing at a level (A) corresponding with 

 the top of the front bars, and leaning forward at an angle of 70° 

 with the horizontal line of the hearth, the back should rise to such 

 a point that the angle where it returns towards the chimney (B) 

 should be vertically over the insertion (C) of the cheeks of the fire- 

 grate. This angle (B) will be about 28 inches from the hearth, or 

 16 inches from the top of the fire, and about 3 J to 4 J inches from 

 the front line of the fireplace, according to the size of the grate. 

 These points will be obvious from the vertical section of the fireplace 

 here shown, and from C, Fig. 2. 



Note. — So far, in the fireplaces built after my rules, the height 

 of the grid from the hearth has been taken at two bricks, or 6 inches, 

 and the height of the bars from the grid also at two bricks, or 6 

 inches. It follows, therefore, that the lean-over commences at 12 

 inches from the hearth. It is possible that a better angle than 70° 

 may eventually be found — such as an angle of 60° — but commencing 

 a few inches above the fire so as not to loiver the angle B where the 

 lean-over returns to the chimney. 



Rule VII. " The shape of the grate should he hased upon a square 

 described within an equilateral triangle, the size to vary in constant pro- 

 portion to the side of the square " (Fig. 2). — The shape of the grate, or 

 grid, is arrived at in the following way : — Describe a square D, of which 

 the sides shall be 8, 9, or 10 inches, according to the size of the 

 room, within an equilateral triangle E, the two sides of which shall 

 represent the " covings " of the fireplace, and the base the front line 

 of the fireplace. From each front angle of the square carry a line 

 from D to C, to the " covings " or sides of the triangle, at an angle 

 of 45° with the front line of the fireplace. These two lines, with 

 the side of the square from which they are drawn, form the front of 

 the grid. The back line of the grid does not correspond with the 

 corresponding side of the square, but is carried IJ inches further 

 back, so as to give greater depth to the grate, and allow the firebrick 

 back to overhang the back of the grid to the extent of IJ inches (see 

 A, Fig. 1) before it ascends as the "lean-over." 



