CH. VII.] THE FRUIT AND SEED. 231 



area of glass in feet, is equal to the cubic feet of air 

 to be wanned in each minute, when there are no 

 double doors. That is 7.5 x30 + 1| X 720 = 1305 

 cubic feet. But in a house ^ith wooden bars and 

 rafters, about -J^th of this space will be occupied 

 with wood-work, which is so slow a conductor of heat, 

 that it will not suffer a sensible quantity to escape, 

 therefore 130 feet may be deducted, leading the 

 quantity to be warmed per minute ==1175 cubic 

 feet. 



To ascertain the surface of pipe required to warm 

 any given quantity of air, multiply the cubic feet of j 

 air to be heated per minute by the difference be- j 

 tween the temperature the house is to be kept at, 1 

 and that of the external air in degrees of Fahren- \ 

 heit s thennometer, and divide the product by 2.1, 

 the difference between 200, which is the temperature 

 of the steam pipes, and the temperature of the 

 house ; the quotient will be the surface of cast iron 

 pipe required. 



Now in the house, the dimensions of which are 

 above given, if the lowest temperatm^e in the night 

 be fixed at 50°, and lO'^ are allowed for winds, 

 and • the external air is supposed to be at zero, 

 or of Fahrenheit, then 1175 multiplied by 60, 

 and the product divided by 2.1, the difference 

 between 200 and 60, will give us the quotient 236 

 =to the surface of pipe required. Now the house 



