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earthy and stony bodies. I nevertheless apprehend, thatfurnaces on this principle, with all the advantages thatcan be given to them, will not be found equal, in regardto the intensity of the heat, to the blast furnace abovedescribed and that air may be supplied more effectuallyby a well contrived wide nosed bellows, than by anyother means whatever. The pressure of the atmosphere,which actuates the wind furnace, is variable, and sub-ject to many irregularities in its effect : but the powerwhich animates the blast furnace, is entirely in the opera-tors hands, and its effect may be increased or diminished,with certainty and regularity, by increasing or diminish-ing the force artificially applied. The wind furnacehowever has its conveniencies; as the fire may be raisedin it to a degree sufficient for most purposes that com-monly occur, and continued without any other troublethan that of supplying fuel.

The structure of our general furnace, already described,unites in some measure the advantages of both kinds ; byaffording an opportunity, when the wind furnace is atwork, of occasionally animating its fire by the blast.The same convenience may be procured also in thewind furnace above described for vehement fire : a hole,made in the side of the foot or ash-pit, serves for ad-mitting the bellows-pipe ; and the air-pipe is at the sametime stopt by means of a moveable register in the endnext the furnace. This register is a circular iron plate,fixt on an axis, which is placed across the pipe : the ex-tremity of the axis projecting on the outside, the plate isthereby readily turned, so as either to allow a free passagefor the air, or to close the whole bore of the pipe.

It is, in many cafes, a very desirable point, to be ableto collect the heat, diffused through a furnace, into one

E particular