2j;$ Vffcnption of an AJfay -furnace. 



5-ioths. This, however, will not be the cafe, though e?^- 

 pofed to a degree of heat approaching to fafion, EE are 

 two fupports for the fcale, attached to the extremity of the 

 plate by means of bolts. FF is a box of wrought iron 

 which contains the bar of Reel exaftly fitted, witli a fmall 

 allowance for expanding in the thicknefs. This box is in- 

 troduced into the lining of the furnace by means of fquare 

 notches formed in the bricks about two inches from the 

 Gonta£l of the fire. The bottom of the box rells upon the 

 uuder-fiange of the cylinder, and its other end rifes through 

 the building and iron-cover about two inches. When at 

 firll introduced into its place, the fpace which may remain 

 betwixt the outfide of the box and the building is carefully- 

 filled with fine charcoal duft, to prevent oxydation by the 

 chance contaft of atmofpheric air. G is a pollflied bar of 

 fteel 3 feet 2 3-4th inches long and i-4th of an inch fquare, 

 the (liarp extremity of which afts upon that part of the lever 

 which, when at C, meafures one inch from the fulcrum. 

 HH, a fmall box or cover, which fits upon the top of the 

 iron box by means of pins. This is always kept full of char- 

 coal-duft, to prevent the approach of external air, and the 

 tranfmiflion of heat from within. 



This.inftrument may be ufed in conjunftion with Mr. 

 Wcdgewood's fcale. Any given fubftance may be melted, 

 and the degree marked upon tlie fcale : let this be compared 

 with the degree of heat at wdiich the fame fubftance melts 

 by Wedgewood's fcale ; then let the greateft degree of heat 

 of the furnace be meafured by one of Wedgewood's rolls, and 

 compared with that pointed out by the index, the one dif- 

 ference divided by the other will give a fcale of comparifon. 

 It will hardly efcape the notice of men of fcience, that 

 circumftances may be fo varied, by the modes of charging 

 the furnace, as to endanger an erroneous refult : but, if pro- 

 per attention be paid, the affayer will foon undcrftand the 

 trim of his furnace fo thoroughly as to be fure of alwayi 

 •btaining fiich an accurate indication of the heat as cannot 

 6 fail 



