THE CULTUEE OF THE GRAPE. 41 



It is the same with air as with water,— the heated be- 

 comes the lighter and ascends ; consequently the cold or 

 heavier descends, and fills the place vacated. 



In the view of the furnace which is given,* the Pol- 

 maise system is attached, the arrows showing the current 

 of heated air over the furnace, and the bending one the 

 rushing in of the cold air to fill the space, and thus the 

 circulation is kept up while the heat is in the furnace. 

 The end view shows the hot-air chamber over the fur- 

 nace ; the two dotted places in this are the openings for 

 the cold air. 



The side view shows also the smoke-flue and the finish 

 of the furnace, with a dead air chamber to receive any 

 ashes that may pass from this and prevent their entering 

 the flue. One opening in the covering of the Polmaise, 

 for the escape of the heated air, is shown, and this cov- 

 ering may be continued as desired, and the heat led by 

 brick, or copper, or other pipes to any spot desired. la 

 the hot-air chamber may be placed j)ans to contain wa- 

 ter, that the heated air may have the required moisture ; 

 these can be regulated at pleasure, having more or less, 

 or none at all, as the state of the house requires. For 

 instance, in the early stages of forcing, you would re- 

 quire all the moisture that could be obtained in this way. 

 If, with such an apparatus, a fire was made to preserve 

 the fruit from frost or other causes after it was ripe, pro- 

 bably no moisture at all would be wanted. 



* This is coi.ied from the Gardenera' Chrouiole, with soiiie slight altera- 

 lions.' 



