230 PEINCIPLES OF GARDENING. [CH. YII. 



circulatory system. A very small boiler will speedily 

 raise the heat of the water, in a very large tank, to 

 1 80 degrees ; and if this heat be imparted late in 

 the evening, it will retain its heat but little di- 

 minished until the morning. The smoke, by means 

 of a flue, /, may be made to impart heat to the house, 

 by passing through it, or may at once enter the chim- 

 ney or pipe attached to the summit of the boiler. 



Hot water in a tank is superior to the same source 

 of heat in pipes, because it is not liable to freeze ; 

 and it is preferable to steam, because its heating 

 power continues, until the whole mass of water is 

 cooled down to the temperature of the house, whereas 

 steam ceases to be generated as a source of heat the 

 moment the temperature falls below 212°. 



If steam be employed, Mr. Tredgold has given 

 the following niles for calculating the surface of pipe, 

 the size of the boiler, the quantity of fuel, and the 

 quantity of ventilation required for a house thirty 

 feet long, twelve feet mde, with the glass four feet 

 high in front ; vertical height of the glass roof eight 

 feet ; length of the rafters foiu'teen feet ; height of 

 the back wall fifteen feet. The surface of glass 

 in this house will be 720 feet supei-ficial, viz." 540 

 feet in the front and roof, and 180 feet in the ends. 

 Now, half the vertical height, 7 ft. 6 in., multiplied 

 by the length in feet, and added to Ij time the 



