Steam and Hot Water fok Gkeenhouse Heating. 169 



indicated by their letters : A, B, C,- D, in houses A, B, C, D, respect- 

 ivel}-, or the steam houses; E. F, in the hot-water house F, E being 

 at the west or boiler end and F at the farther end. The thennoni- 

 eters inserted inside the pipes are designated by small letters, to 

 correspond with the respective series of houses. Part of these 

 latter are in the risers and part in the returns, as indicated in the 

 table. These inside riser thermometers were inserted near the 

 heater, before the riser entered the house; and the return ther- 

 mometers were inserted near them or after the pipes had left the 

 house. 



Eeturn thermometer a b is inserted in the pipe which takes 

 the return from the middle and upper benches of house A and 

 B; those from the lower bench passing back, by a separate pipe 

 to the general steam return. Return thermometer c d is in the 

 pipe which carries the return from all the runs of house C and D. 

 The mercury in this thermometer was occasionally found to fluctu- 

 ate back and forth with a comparatively uniform and rapid 

 motion. Whenever this was the case, the figures are given which 

 show the extent of the range. This thermometer being in the 

 return near the boiler, there was probably a backward pressure 

 at times, forcing some of the heat into the return, which at this 

 point is below the water level in the boiler, and nearly horizontal. 

 A slight tendency to a similar action was noted in the other series 

 once or twice (return a b), but that thermometer is in an upright 

 portion of the return, nearly as high as the top of the boiler, 

 where such an effect was not to be expected. 



It will be seen by the table that on the mornings of February 

 twenty-third, twenty -fourth, twenty-fifth, twenty-sixth and twenty- 

 ninth, there was practically no circulation in the pipes of houses 

 C and D. These were warm mornings and the fires were low, 

 hence in computing the averages of the thermometers on this 

 run more reliable figures are obtained by disregarding these 

 observations, and such modified figures are used in comparison 

 in the summary of Table 1, although the actual averages obtained 

 by including these are also given in parentheses. This is of 

 little importance in the return, where the temperature is change- 

 able, for it there modifies the average but slightly. 



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