THE CULTURE OF THE GRAPE. 29 



house. An opening must be provided on the top of the boiler, 

 or tank, to fill these with the water. 



THE POLMAISE SYSTEM OF HEATING. 



Much discussion has been held of late in England, relative 

 to this mode of heating green and other houses for horticul- 

 tural purposes, and some curiosity has been excited in this 

 comitrj as to Avhat the system is. The principle is similar 

 to that upon which many of our churches and dwelling-houses 

 have, for many years, been warmed. It is the same with air 

 as with water, — the heated becomes 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 Polmaise 

 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 furnace ; 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 covering may be continued 

 as desired, and the heat led by brick, or copper, or other 

 pipes to any spot desired. In the hot-air chamber may be 

 placed pans to contain water, 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 require 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, probably 

 no moisture at all would be wanted. 



* This is copied from the Gardeners' Chronicle, with some slight alterations. 



