' EXPLANATION arid OBSERVATIONS to. Plate II. p. 97. 
a Fire-houfe. 
h b Fire-places, which comniunicate with the flues c c 
c c Firft flues. 
d d Second flues. 
ee Third flues. . 
f f Fourth flues. 
One fire ought not to be allowed to work more than about thirty r'eet in 
length, becaufe by the time it has made four returns, (viz 120 feet) its heat is 
generally nearly fpent. As the heat decreafes proportionable to the diftance from 
the fire-place, the diminifhing of the dimenfions of the flues is obvious. On this 
account, feme Perfons who give defigns for building of Hot-walls, recommend 
a brick on edge inftead of a brick in breadth, for the front of the two uppermoft 
flues. When this expedient is intended, it will be proper to have narrow bricks^ 
of the thicknefs of common bricks, made on purpofe to fuit the work — But when 
the wall is intended to be drawn with ftucco, this laft precaution will be unne- 
ceflary. 
