400 FORCING DEPARTMENT. 



the inner one is carried up to within a foot of the level 

 for the wall plate, and a cavity of four inches left 

 betwixt the two, which is left open at top. The 

 centre of the external wall between the piers, is formed 

 into pannels, with thin tiles placed on the edge, 

 (and set in cement,) in order that the heat produced 

 from the dung linings may penetrate rapidly through 

 them into the vacuity, when it ascends and warms 

 the atmosphere of the pit with dry heated air, free 

 from all the obnoxious effluvia that arises from dung- 

 when applied in a recent state. This cavity is a 

 very advantageous contrivance, as it prevents, also, 

 much of the moisture, accruing from the ferment- 

 ing materials, getting into the pit ; a too great degree 

 of which is often very injurious to the plants in the 

 Winter season, particularly if the atmosphere of the 

 pit is not kept in a warm and congenial state. This 

 is often a matter of some difficulty, from the sudden 

 changes of the weather,, especially in large establish- 

 ments, where there is a large supply of accelerated 

 vegetables required, and various other articles, 

 whose growth is promoted by dung heat ; which 

 renders the consumption of this material of no small 

 importance. The pit is about 70 feet long, 6 feet 

 9 inches in the clear inside measure from the two 

 interior walls ; the back wall is eight feet high ; the 

 front five feet ; the entire pit is sunk three feet under 

 the ground level, and is surrounded by an external 

 dung pit, where the linings are applied, of about two 

 and a half feet wide. The exterior wall of this pit 

 consists of nine-inch brick work, which is carried up 

 to the ground level, and there coped with a three 



