28 



200 and 60, will give us the quotient 236 = to the 

 surface of pipe required. Now the house being thirty 

 feet long, five pipes of that length, and five inches in 

 diameter, will be about the proper quantity. 



If hot water be employed instead of steam, the 

 following proportions and information, obtained from 

 Mr. Rendle, may be adopted confidently as guides.. 

 In a span roof propagating house, forty feet long, 

 thirteen feet broad, seven feet high in the centre, 

 and four feet high at the two fronts, having a super- 

 ficial surface of glass amounting to 538 square feet, 

 Mr. Rendle has a tank of eighty-three feet long, 

 running round three sides of the house, four feet wide 

 and about eight inches deep, and consequently capable 

 of containing nearly 300 cubic feet of hot water, 

 though only half that quantity is used. This is 

 closely approaching to the size pointed out, according 

 to Mr. Tredgold's formula. The mean temperature 

 of a hot- water tank will never be much above 100 

 degs., so that for the sized house mentioned by that 

 skilful engineer, the divisor must be 2.1 times the 

 difference between 100 and 60 degs., which gives as 

 the quotient 335 cubic feet. 



The tank in Mr. Rendle' s propagating house is 

 lined with Roman cement, and if the temperature 

 at the time of lighting the fire be 90 degrees, the 

 temperature of the atmosphere of the house Q7 de- 

 grees, and the temperature out of doors 50 degs., the 



