construction is the most simple, and which, of course, are the cheapest, are beyond comparison the best, on all accounts. Nothing being wanted in these chimneys but merely a grate for containing coals, and additional apparatus being not only useless but very pernicious, all complicated and expensive grates should be laid aside, and such as are simple substituted in their stead. In the choice of a grate, beauty and elegance may easily be united with perfect simplicity. Indeed, they are incompatible with everything else." Again he says, "Iron, and in general metals of all kinds, are to be reckoned among the very worst materials that it is possible to employ in the construction of a fireplace."
Rule II. "The back and sides of the fireplace should be of brick, or fire-brick."—Brick retains, stores, and accumulates heat, and radiates it back into the room, and keeps the fuel hot. Iron lets heat slip through it up the chimney, gives very little back to the room, and chills the fuel. On this point also Rumford speaks very strongly. "The best materials I have hitherto been able to discover are firebrick and common bricks and mortar. . . . The fuel, instead of being employed to heat the room directly or by the direct rays from the fire, should be so disposed or placed as to heat the back and sides of the grate, which must always be constructed of fire-brick or fire-stone, and never of iron or any other metal."
Rule III. "The fire-brick back should lean over the fire, not lean away from it," as has been the favorite construction throughout the kingdom. The lean-over not only increases the power of absorbing heat from rising flame—otherwise lost up the chimney—but the increased temperature accumulated in the fire-brick raises the temperature of gases to combustion-point, which would otherwise pass up the chimney unconsumed, and thus be lost. Rumford discovered accidentally the value of this "lean-over," and at once realized its immense importance. He does not, however, seem to have carried out his intention of working out for general adoption this form of back.
He first of all condemns to alteration all fire-backs which lean away from the fire. "It frequently happens that the iron backs of grates are not vertical, but inclined backward. Where the grates are wide, and can be filled up with fire-brick, the inclination of the back will be of little consequence, since, by making the fire-brick in the form of a wedge, the front may be made perfectly vertical, the iron back being hid in the solid work of the fireplace. If the grate be too shallow to admit of any diminution, it will be best to take away the iron back entirely, and cause the vertical back of the fireplace to serve as the back to the grate."
He next describes his discovery of the value of the "lean-over": "In this case I should increase the depth of the fireplace at the hearth to twelve or thirteen inches, and should build the back perpendicular to the height of the top of the burning fuel, and then, sloping the back
