RADIATING AND GLASS SURFACE. 85 



generally discarded. It is one of the misfits between theory and 

 practice that often occurs. 



It may be of interest to give tables prepared by B. A. Dud- 

 ley, representing a reliable heating and ventilating manufactur- 

 ing company. The following will be found a safe proportion men t 

 of heating surface to glass surface for various temperatures in the 

 greenhouses, when the temperature is at zero outside, with not 

 to exceed five pounds steam pressure at the boiler: 



TABLE I. 



PROPORTION OF HEATING TO GLASS SURFACE FOR MAIN- 

 TAINING DIFFERENT TEMPERATURES IN 

 GREENHOUSES. 



Having determined the amount of heating surface, the next 

 point is its distribution, and for this nothing gives better results 

 than the "over-head" and "under-bed" system. This system 

 consists in carrying the flows through the peak of the house to 

 the end farthest from the boiler, then droDping and returning in 

 small pipes, preferably one-inch under tuc teds. 



