1886.] on the Principles of Domestic Fireplace Construction. 347 



essential. But there is gain, thereby, in another direction. It 

 affords plenty of room for the burning fuel to lie down close to the 

 grid, and away from swift air currents, and prevents the tendency of 

 the fire to burn hollow. 



On this point Eumford has a word to say : — " But as many of the 

 grates now in common use will be found too large when the fireplaces 

 are altered and improved, it will be necessary to diminish their 

 capacities by filling up with pieces of firebrick. But in diminishing 

 the capacities of grates, care must be taken not to make them too 

 narrow, i. e. too shallow. 



" The proper depth for grates for rooms of middling size will be 

 from six to eight inches. But where the width (i.e. depth) is not 

 more than five inches, it will be very difficult to prevent the fire going 

 out." (III. 520.) 



"Where grates designed for rooms of middling size are longer 

 (and broader) than 14 or 15 inches, it will always be best to diminish 

 their length by filling them up at their two ends by firebrick." 

 (III. 522.) 



Rule V. " The sides or ' covings ' of the fireplace should be inclined 

 to one another as the sides of an equilateral triangle " (Fig. 2, p, 350). — 

 The working out of this rule has cost me much thought and experi- 

 ment. It was worked out more or less emjiirically with a view to 

 attain certain objects, and, having attained them, I discovered that I 

 had unwittingly selected the sidos of an equilateral triangle. It is of 

 some importance, and may be of interest, to tell how the question 

 arose. In my earlier fireplaces the sides or " covings " were parallel 

 to each other, and had the defect that they radiated most of their 

 heat from one to the other, not into the room, with the probable result 

 that much of such heat would eventually escape up the chimney. 



It was clear then that the sides must be set at an angle with the 

 back, so as to face towards the room. But at what angle ? My first 

 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 Eumford 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 of)en- 

 ness 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 deter- 

 mine 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 Rumford's fireplaces, are at a right angle to each other, 

 this perpendicular line misses the opposite margin by several inches. 



