AATD COXSKnV.VTOKT. 33 



in a tank or otherwise any extra amount of heat which may be 

 carelessly applied in the furnace. 



Let B represent a common boiler, havinfra feed cistern (c) ; 

 let E and r be the ordinary flow and return pipes for heating 

 the greenhouse, under the floor of which is placed the rain- 

 water tank (n). All this will be seen to consist of what is 

 found in an ordinary greenhouse only. The rest can be added 

 to any common house and heating apparatus, and consists of 

 a layer or coil of pipes (i) in the bottom of the tank, and com- 

 municating with the return pipe and boiler at k; while from 

 the other end of this coil is fixed the pipe (r,) terminating in 

 a cistern (m), the bottom of which is on the same level as 

 that of the feed cistern (c). An upright pipe (n), with a 

 sliding tube (o), marked with degrees, is attached to the flow- 

 pipe (e), and also enters the aforementioned cistern (m). The 

 tube (o) regulates the whole affair, according to its position ; 

 e. g. if this tube be raised one inch above the level of the water 

 in the cistern and return-pipe (ii) no circulation can take 

 place through the coil unless the water be heated some 40°. 

 If the orifice of the tube (l) be ten feet above the bottom of 

 the boiler, and that of the tube (o) ten feet one in'ch, the cir- 

 culation will commence only through the coil when the tem- 

 perature of the water in the pipes exceeds 100° (the ordinary 

 circulation will at all times proceed through the pipes in the 

 greenhouse). If the temperature of the water be required to 

 be 180°, the sliding tube would have to be raised about four 

 inches above m ; this is reckoning the water there to be about 

 40° ; and it will be seen that these calculations are based on the 

 table given at the beginning, and that no deduction is made 

 for the water becoming slightly heated in the return-pipe (m) ; 

 this being done for clearness. I find this is easily got over 

 by the graduating of the tube (o) accordingly (the cistern 

 (m) ought to be kept cold by a stream of air). The reader 

 will see that no water can circulate only in the ordinary 

 manner, unless the heat of the same exceed what is required ; 

 in that case it will, instead of flowing only through the 

 pipes in the greenhouse, leave them and flow through the coil 

 in the cold-water tank, and entering the boiler almost as cold 

 as that in the tank, and continue to circulate through these 

 until it becomes sufliciently cold to again flow through the 

 pipes in the greenhouse. 



In small greenhouses a very large fire may be made up 



