220 Description, with Plans of a Hot Wall. 



trained upon the wall. In every other respect the wall is the 

 same, only the thickness in front of the upper horizontal flue 

 is three inches. The furnace is provided with an outer and 

 inner cast-iron door, and ash-pit door, and the outlet of the 

 flues with a cast-iron chimney top, having a lifting damper. 

 In heating the wall the furnace door is always kept close, ex- 

 cept when feeding the fire ; the ashpit door being allowed to 

 stand open as much as to make the fire burn to the extent 

 required. When the wall has been brought to the proper 

 temperature, the damper on the chimney top is let down, and 

 the ash-pit door closed ; a few red embers shut up in the 

 furnace will assist in preserving the heat, which may thus be 

 maintained for a considerable time, and a saving of fuel 

 effected. In summer all the furnace doors are to be kept 

 close, and the top dampers let down. For a further descrip- 

 tion of these plans I beg to refer you to the particular refer- 

 ences which accompany them. 



I am, Sir, 

 Your most obedient Servant, 



Edinburgh, John Hay. 



July 15, 1826. 



References to the annexed Plan, and Sections. 



Fig. 1 . The ground plan. One side A has a recess for a 

 wooden trellis, the other side B is without a trellis, 

 but has in lieu of it a warm air flue a. The furnaces, 

 flues, cleaning holes, &c. are shown, bb, are holes 

 three inches square, at the level of the fire bars, 



