174 



HEATING AS APPLIED IN HORTICULTURE. 



that in the meanwhile the cold air at e 

 presses downwards into the drain, in con- 

 sequence of the abstraction of air from /, 

 and, rushing along in the direction e /, 

 produces a general circulation of all the 

 air of the house : in other words, the 

 pipes / act so as to suck the cold air out 

 of the house along the drain e f, and 

 having heated it, send it upwards again 

 into the house through the aperture c, 

 when it again descends to e. 



" It would be extremely difficult to 

 conceive anything more unphilosophical 

 than this singular contrivance. In the 

 first place, the whole heating apparatus 

 is placed on the outside of the house it is 

 intended to heat ; and this alone must, 

 from the nature of Mr Penn's other 

 arrangements, cause an immense waste of 

 heating power ; and, in the next place, 

 the heated air is forced downwards, in 

 the opposite direction to that which it 

 would naturally take ; — in order to effect 

 which a still further heating power is 

 to be provided, for no circulation, such 

 as would be required to produce the 

 necessary temperature of a greenhouse in 

 cold weather, can be thus maintained, if 

 at all, except by an extraordinary crea- 

 tion of heat at /. It is clear, therefore, 

 that one part of the supposed advantages 

 of Mr Penn's method — namely, that of 

 economising fuel — does not belong to 

 it." 



It appears to have been Mr Penn's 

 object to effect ventilation and circula- 

 tion of the air within the house — both 

 matters of very great importance. If by 

 ventilation we are to understand the 

 admission of a supply of fresh air, then, 

 in this case, we have none ; for, presum- 

 ing that there is a circulation, it is only 

 of the air in the shed flowing into the 

 house, and the air of the house flowing 

 back again into the shed. This is cer- 

 tainly the case in cold weather, when 

 supplies from the external air are shut 

 out, and therefore the same air, or nearly 

 so, keeps circulating until it can be of 

 little use to plants ; and if the shed and 

 house were perfectly air-tight, it would 

 soon become dangerous to breathe in it. 



The commentator on the above mode 

 of heating has shown by the opposite 

 diagram, fig. 209, "a plan of heating 

 without loss of heat or departure from 

 established principles, which would have 



Fig. 209. 



effected the circulation attempted by 



Mr Penn. 

 "Suppose," 

 says he, 

 "in the an- 

 nexed dia- 

 gram, acd 

 represent - 

 ed the sec- 

 tion of a 

 g reen- 

 house : if 

 / e is the 

 drain, and 

 the pipes 

 are sta- 

 tioned at e, no principle would be vio- 

 lated, no heat w T ould be lost, and a circu- 

 lation would be established all round the 

 house in the direction of the arrows." 



A very fair trial was given to Penn's 

 system by Sir Joseph Paxton in heating 

 an orchid house at Chatsworth, of which 

 the annexed fig. 210 is a section. This 



Fig. 210. 



house is covered with a thatched mov- 

 able roof a, travelling upon rails placed 

 on the side walls at b b, and almost 

 sufficient of itself to repel ordinary frosts. 

 Notwithstanding, four courses of pipes 

 were laid all round the house, and double 

 the quantity of fuel consumed that would 

 have heated it sufficiently upon any of 

 the ordinary methods of hot-water heat- 

 ing ; while Mr Penn was left uncon- 

 trolled by Sir Joseph, who, with great 

 liberality, wished to give the system a 

 fair trial. He not only failed in heating 

 the house, but the expense was above 

 ,£130 greater than Walker of Manches- 

 ter had contracted to do it for. c c is the 

 casing in which the pipes are enclosed ; d 

 the roof of the house. 



