192 MASSACHUSETTS HORTICULTURAL SOCIETY. 



I would construct the flow-pipe in such a manner, as it passes 

 from the boiler, as to immediately empt}' itself into a stand or 

 expansion pipe near the boiler, and on the top of this stand-pipe I 

 would have a valve which would open under a definite pressure, 

 liable to be generated in case of the great heat in the water induc- 

 ing steam and otherwise entailing an explosion. 



Some persons — and I am one of them — assume to say that the 

 accumulation of steam in this stand-pipe will act as a force, pro- 

 vided the valve is weighted, propelling the hot water through the 

 radiating pipes, thereby very much increasing its natural velocity, 

 and returning it again to the boiler before it loses its heat. I can- 

 not say, from actual experience, whether this stand-pipe will act 

 as a force or not, but am confident it will so act, and that this 

 theory will stand the tests of science and experience against any 

 other theory. 



I have never yet seen the expansion-pipe thus placed near the 

 boiler ; \et, when we reflect on the action of hot water and steam, 

 it seems to me that this is the proper place for it, and I hope that 

 the plan I now propose will so commend itself to some enterpris- 

 ing horticulturist that it will be tried at once, for I believe that 

 in this way, and this onh", can we accelerate the flow of hot water ; 

 and therein lies the whole secret of successful heating. I conceive 

 that this stand-pipe can be placed in such a position in the green- 

 house, and the flow can be taken from it at such a depression, 

 as to preclude the necessity of placing the boiler below the level 

 of the surface of soil in the greenhouse. This is another very 

 important point in construction, and is worth}' of great attention. 

 Ever}- l)oiler-pit I know of is a dark, damp hole, exceedingly 

 objectionable in every possible way, often filled with water, and 

 disagreeable to enter. But, with the method of construction I 

 suggest, the whole arrangement will be on the surface of the 

 ground, and the care of the fire can be looked at as a pleasure 

 rather than a dread. 



The cliimne}- should receive the smoke on a level with the grate, 

 or lower down, so that all the gases from the coal will be 

 consumed over .the fire and among the pipes constituting the 

 boiler. 



The radiating pipes in the greenhouse are to be in number suflji- 

 cient to properly heat the space required, and no viore. To have 

 more than enough pipes is detrimental, because the surplus causes 

 the water to move sluggishly, whereas our object is velocity, and 



