198 MASSACHUSETTS HORTICULTURAL SOCIETY. 



pipe, it would work twenty-five per cent better. The only advan- 

 tage in running a water circulation under pressure is to be found 

 in the slightly higher temperature which can be gained. Pressure 

 is solely from the effect of steam. A pressure of five pounds to an 

 inch, equal to about eleven feet head of water, would raise the 

 temperature of the water when boiling to 238°, instead of 212° as 

 in the case of open pipes. When we run under pressure we require 

 stronger apparatus and tighter joints ; and, if pressure were to be 

 used at all, he would prefer steam, which is yevy easily managed. 

 There will be a tendency to form globules of steam, which will rise 

 in vertical pipes, and ever}- particle must be replaced by the re- 

 turn-pipe. You cannot heat pipes by the plan of the essayist: 

 there would be no heat in tlie two lower pipes ; the water will 

 take the shortest route to return. The most intense heat applied 

 to the surface will not heat water a foot below it. 



The speaker formerly objected to steam, but has modified his 

 opinion in regard to it. He spoke of George Hill's house, at Ar- 

 lington, as one which it would repay all interested to visit. Mr. 

 Hill has the newest arrangeuients, and one foot of surface of the 

 steam-pi|)cs heats thirty cubic feet of the greenhouse. He has an 

 upright boiler, which is the best heating unit, and the steam goes 

 to the end of the house, and returns by six pipes an inch and a 

 quarter in diameter. He uses a pressure of one pound to the 

 square inch. Tliere is a compensating valve by which a uniform 

 pressure, equal to 215°, can be maintained for ten hours during sud- 

 den and severe changes of weather. The pressure could be in- 

 creased if desirable ; but it is not. The adjustment is simple and 

 automatic. One of the advantages o'f steam over water is that it 

 takes but very little time to heat up or to cool off the pipes, and, 

 with good apparatus in good hands, it is more easily managed 

 than hot water. Another advantage is, that steam affords the 

 easiest way to moisten the air of the house when too dr}' ; which is 

 a protection against freezing in cold weather. A house will cool 

 off more quickly if the air is drj' than if moist, because the capac- 

 ity of moist air for heat is three times as great as that of dr}- air. 



The studv of this subject will be more profitable to the owners 

 of greenliouses than that of any other ; indeed, it has an application 

 to every part of life. Some kinds' of glass will transmit the heat 

 of the sun better than others. Great care is needed in the selec- 

 tion of glass for greenhouses. Any one wishing to understand the 

 very complex questions offered by the subject of heating would do 



