BOOK VII. 



227 



hearth, for it does not project beyond the wall. The hide of the bellows is 

 fixed to the bellows-boards with its own peculiar kind of iron nails. It joins 

 both bellows-boards to the head, and over it there are cross strips of 

 hide fixed to the bellows-boards with broad-headed nails, and similarly 

 fixed to the head. The middle board of the bellows rests on an iron bar, 

 to which it is fastened with iron nails clinched on both ends, so that it cannot 

 move ; the iron bar is fixed between two upright posts, through which it 

 penetrates. Higher up on these upright posts there is a wooden axle, with 

 iron journals which revolve in the holes in the posts. In the middle of 

 this axle there is mortised a lever, fixed with iron nails to prevent it from 

 flying out ; the lever is five and a half feet long, and its posterior end is 

 engaged in the iron ring of an iron rod which reaches to the " tail " of the 

 lowest bellows-board, and there engages another similar ring. And so when 

 the workman pulls down the lever, the lower part of the bellows is raised and 

 drives the wind into the nozzle ; then the wind, penetrating through the hole 

 in the middle bellows-board, which is called the air-hole, lifts up the upper 

 part of the bellows, upon whose upper board is a piece of lead, heavy enough 

 to press down that part of the bellows again, and this being pressed down 

 blows a blast through the nozzle. This is the principle of the double bellows, 

 which is peculiar to the iron hoop where are placed the triangular crucibles in 

 which copper ore is smelted and copper is melted. 





A IRON HOOP. B DOUBLE BELLOWS. C ITS NOZZLE. D LEVER. 



I have spoken of the furnaces and the iron hoop ; I will now speak of 

 the muffles and the crucibles. The muffle is made of clay, in the shape 

 of an inverted gutter tile ; it covers the scorifiers, lest coal dust fall into 

 them and interfere with the assay. It is a palm and a half broad, and the 

 height, which corresponds with the mouth of the furnace, is generally a palm, 



