Construction of Melon, Phie, and Plant Pits. 



459 



Fig. 42. Section of a Pine-Pit. 



having a greater volume of air between the soil and glass, is to 

 be heated by hot water when it is necessary. A pit so large 

 will seldom be over-heated, and therefore no vacuity is shown 

 within the walls ; but, should it at any time become so, the lining 

 must be prised back with a stick, to admit cooling air to the 

 walls. One of Rogers's conical boilers is shown in the plan, 

 Jig. 43., as also the pipes (g), flue (h), and chimney (i) ; the piers 

 ;— TTfi are shown at k, and those of 



XM i ^ ^ ^ the front wall support the 



"" ' : " "7lf|l"^~7 pipes, as expressed in the sec- 

 The lights on this pit 

 are at an angle of 23° to the 



Fig. 43. Plan of Part of a Pine-Pit, showing 

 Rogers's Boiler and Pipes. 



Fig. 44. Section of a Plant- Pit. 



horizon, which is considered to be the most suitable angle for 

 the purpose. 



Fig. 44. is a plant-pit, sunk 18 in. into the ground, and filled 



