Steam and Hot Watek fok Gkeenhouse Heating. 175 



water pipes was much more limited, but there does not seem to 

 be such a uniform difference between outside and inside readings' 

 with increase of temjx^rature an with the steam. The results in 

 Table I plainly show a considerable variation at diiferent points 

 between the outside and inside temperatures, but how much of 

 this is due to differences in painting, radiating powers of the 

 pipes, etc., and how much to the crudeness of the method, it is 

 impossible to say. Thermometer riser A shows a temperature 

 differing not more than 18 degrees, on the average, from that of 

 the inside of the pipe; that on riser C shows 16 degrees variation 

 from the inside temperature, but as there was a difference of 

 some twenty feet between this and its twin inside thermometer 

 c d, the real difference is probably not more than 15 degrees. 



It is evident from this study of radiation, that the higher the 

 inside temperature the less is the proportionate warming power 

 of the pipe at a given point; and as a higher temperature and more 

 rapid flow are ordinarily canied with steam than with hot water, 

 steam has the advantage in carrying long runs. It is said, how- 

 ever, that much of the fierce heat of rapidly moving steam is 

 returned to the hea/ter and is lost as a direct warming agent; but 

 this depends entirely upon the length of the run. It is to be 

 expected that the relative merits of steam and hot water for 

 green-house heating depend very much upon the sizes and shapes 

 of the houses, and it is surj^rising that these conditions are so 

 little considered. The distribution of heat in our two systems 

 should now be discussed, for it will throw much light upon the 

 whole question. 



3. Distribution of heat in the pipes. — We will now compare 

 the temperatures at extreme ends of the different systems, both 

 in risers and returns, in order to detenu ine where the heat is 

 transferred to the athmosphere of the houses. Table II, shows 

 the average temperatures, during the whole time, inside the risers 

 and returns, and on the outside of the risers, at opposite ends of 

 the houses. The inside thermometers in all the risers, and in 

 the returns from the steam houses, were about twelve feet from 

 the heater; those in the hot water returns were some twenty or 

 twenty-five feet from the heater. 



