102 : THE PRINCIPLES OF FLORICULTURE 



dress before the students in floriculture at the Massa- 

 chusetts Agricultural College, F. J. Elder, then heating 

 engineer for Lord & Burnham, considered this topic in a 

 clear, logical way. He spoke as follows: 



" A greenhouse is, without doubt, the most difficult of 

 all structures to heat, and is, it might be said, the least 

 responsive to scientific calculation to ascertain the re- 

 quired quantities of radiation. This is due to the great 

 susceptibility of a greenhouse to the cooling effects of 

 winds. If outside air were at all time quiet air, the 

 heat loss per square foot of exposed surface would be 

 constant, notwithstanding the fact that the openings 

 between the lapped lights of glass are not at all of the 

 same size. Excepting sheet iron only, glass is, of all 

 building materials, the greatest conductor of heat, and 

 all greenhouse radiation must be figured in ratio to the 

 exposed glass surface or its equivalent in other exposed 

 surfaces. The ratios following have been used by Lord 

 & Burnham Company for years, and have given satis- 

 faction. " 



TABLE OF FACTORS FOR FINDING THE NUMBER OF SQUARE FEET 

 OF PIPE SURFACE REQUIRED TO HEAT WITH HOT-WATER TO 

 DIFFERENT TEMPERATURES IN GREENHOUSES WHEN THE OUT- 

 SIDE TEMPERATURE is AT ZERO 



" For 70 to 75 divide square feet of glass and equiva- 

 lent by 1.8. 



" For 65 to 70 divide square feet of glass and equiva- 

 lent by 2.28. 



" For 60 to 65 divide square feet of glass and equiva- 

 lent by 2.62. 



" For 55 to 60 divide square feet of glass and equiva- 

 lent by 3. 



