240 THE POPULAR SCIENCE MONTHLY. 



experiments were determined by the shape of the corner bricks which 

 were in the market. These determined the inclination of the sides to 

 be such that, if prolonged, they would meet at a right angle. This is 

 the angle laid down by Rumford as the angle of selection, but as the 

 largest angle admissible in a good fireplace. This angle, however, 

 brought me into difficulties with my " lean-over " back. The openness 

 of the angle made the back, as it ascended, spread out so rapidly that 

 what was gained in width was lost in height. Moreover, my critics 

 objected to its appearance as ugly. What, then, should determine the 

 inclination of the sides ? The point was thus determined : Seeing 

 that a heated brick throws off the greatest amount of radiant heat at 

 a right angle with its surface, the " covings" should be at such an 

 inclination to each other that the perpendicular line from the inner 

 margin of one " coving " should just miss the outer margin of the 

 opposite "coving." Where the " covings," as in my earlier attempts 

 and in Count Rumf ord's fireplaces, are at a right angle to each other, 

 this perpendicular line misses the opposite margin by several inches. 

 It was clear, therefore, that 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 

 with the back ; but I have expressly said that they should never ex- 

 ceed 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." 



Rule VII. " The ' lean-over"* at the back should be 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 toward the chimney (B) should be vertical- 

 ly over the insertion (C) of the cheeks of the fire-grate. This angle 

 (B) will be about twenty-eight inches from the hearth, or sixteen inch- 

 es from the top of the fire, and about three and a half to four and a 

 half 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. 



So far, in the fireplaces built after my rules, the height of the grid 

 from the hearth has been taken at two bricks, or six inches, and the 

 height of the bars from the grid also at two bricks, or six inches. It 

 follows, therefore, that the lean-over commences at twelve inches from 

 the hearth. It is possible that a better angle than 70 may eventually 



