93 



light may be opened in this way, so that a workman 

 may get to any part of the pit. (Gard. Chron. 1844, 

 69.) 



Mr. Knight's pit was also heated by dung heat 

 only, but applied by means of linings. It was con- 

 structed of a hollow wall, nine inches thick, with 

 sound, even-sized bricks, placed edgeways, the joints 

 being carefully made, and laid with the very best 

 mortar. The bricks placed with their faces and ends 

 alternately to the outside, so that those which have 

 their ends exposed become ties to the surfaces of the 

 wall. In each succeeding course, as the wall is built, 

 the bricks with their ends outwards are placed on the 

 centre of the bricks which are laid lengthways in the 

 course below. Thus a hollow space is formed in the 

 middle of the wall, of four inches in width, which is 



