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plate, which, for this purpose, is made about two incheswider than the door, and as long as the height of the hoopwill admit it to be. The fuel is put in, as before, throughthe fire-place door of the dome. As the part of the fur-nace above the grate widens downwards, the coals gene-rally of themselves fall properly round the muffle : if thisshould not happen, they are easily pushed down by meansof a crooked iron wire introduced through the door. Thedome is lifted off, as in the wind-furnace, by an ironrod passed through its opposite apertures.

The foregoing combination, of the two pots and theiron hoop, with or without the chimney or a part ofit according as a greater or less degree of heat is required,serves also as a reverberatory, for distillation in coated glassretorts, earthen retorts, or longnecks ; with only thisvariation in their disposition, that instead of the largegrate, the middle one is introduced into the undermostpot, and in its upper part two iron bars are laid across :the bottom of the distilling vessel rests upon these bars,and its neck comes out at the door of the hoop, which isaccommodated to vessels of greater or less height by placingit with the door uppermost or lowermost. Both the re-verberatory and the assay furnace are, in effect, no otherthan the wind-furnace; with a muffle or a retort set inthe fire instead of a crucible.

These furnaces may be used likewise as a commonstove, for keeping a room warm with a little quantity offuel. There are three general intentions which havebeen pursued in contrivances for this purpose ; (i) makingthe fuel take fire by degrees, and consume siowly; (2)conducting its heat, or the air warmed by it, through anumber of passages or circumvolutions, that the heat,

instead