furnace,) to hang over the fire-place in the centre; this in time enlarges by burning away, and causes them to crack at the bottom or back, by cold draughts through the fire-bars, if holes are too suddenly opened beneath by the tiseur, for the admission of air to urge the heat of the furnace after pot-setting. Occasionally, too, when the centre part of the siege has been partly destroyed by the flame, a pot full of liquid Glass has been known to fall back into the fire-place or grate; and, as the intense heat prevents any means of raising it again to its erect position, with iron boat-hooks, which become straightened by the melting heat of the furnace, the back of the pot must of necessity be tapped with an iron bar through the grating below, and the whole contents allowed to run into the arch beneath the furnace. The author has been present on such an occasion, and finds it difficult to describe the awful beauty of the prismatic colours of the liquid fire, as it showered into the cave.

Ten pots of thirty-six inches diameter are the medium number for a well proportioned furnace, and are found the most economical for fuel.

The crown of the furnace should be as low as can be built, to support itself, and to admit the pots, that the fuel may not be wasted by heating a useless interior area.

The consumption of fuel by a well constructed ten-pot furnace will be from eighteen to twenty-four tons of coals weekly, in the furnace only. A furnace of twelve pots, exposing a much larger unoccupied area, in comparison with a ten-pot furnace, will consume nearly double the quantity of fuel; whereas, twelve pots of melted metal will hold only in the proportion of one-fifth increase. Furnaces of less dimensions