STEAM. 



321 



manner exhibited in the two following figures. The 

 cistern is covered with pavement, over which is a bed 

 of small stones, then ashes or sand, into which the pots 

 containing plants are to be plunged. 



Fi- 25. 



^^w^=^^ds^^m 





Steam has also been employed to heat flues. The fol- 

 lowing figure represents a side view and section of a flue 

 filled with small stones or broken bricks, and heated 



Fig. 26. 



by means of a small steam-pipe passing along the lower 

 part of the flue. Along the upper side of this pipe arc 

 a number of small holes, becoming more frequent to- 

 wards the farther end, to allow the escape of steam: 

 there are, besides, a few perforations in the under side 

 to clear away condensed water. The flue has a slight 



