INTRODUCTION. 



The followiiifj: discuission of some of tlie comparative merits of 

 steam and hot water for greenhouse heating is adapted from a 

 thesis pre]iared for a bachelor's degree by Fred W. Card, who is 

 at present a Fellow in Horticulture. The inspiration of the thesis 

 lay in the facts that the subject itiself is now much discussed by 

 greenhouse men, and that the few experiments which have been 

 made seem to consider chiefly but one item — the coal consiunp- 

 tion — in the merits of the two systems. If we are to arrive at 

 definite results concerning the relative merits of steam and hot 

 water for warming glass-houses, we must consider jiot only the 

 consumption of coal, but the original cost of th<? systems, their 

 adaptations to particular purposes, and comparative ease with 

 which they can be managed. At the outset of our investigation 

 we asked ourselves the question, " Where is the heat expended in 

 the two systems?" It is evident that two heating jilants which 

 make the same amount of heat and carry it throughout houses of 

 equal size may distribute this heat differently, and therefore vary 

 widely in usefulness. We have endeavored to ascertain how much 

 heat left the heater and how much returned to it, how rnnch was 

 expended near the heater and how much was carried to tlie farther 

 end of the runs, how much escaped from the risers as top heat and 

 how much from the returns as bottom heat. These questions, and 

 many others, can not be studied by taking the air temperainres of 

 the houses. In fact, air temperatures taken at stated intervals 

 seldom afford a 'satisfactory measure of the actual cnditicns of 

 the houses, for they do not show the incidental variations, and 

 they often overlook the temperature at the :nost critical periods ; 

 this fact is well illustrated in the air records of ou>' houses in the 

 following pages, which give the highest average for the hot water 



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