188 



HEATING AS APPLIED IN HORTICULTURE. 



increasing it ; but the only result of his 

 labour is the more rapid destruction of 

 the boiler itself. Until the publication 

 of Hood's work above mentioned, the 

 principle of circulation in hot-water ap- 

 paratus was very little understood ; most 

 erroneous notions prevailed on the sub- 

 ject ; and where the principles were un- 

 known, and opportunities of experiment 

 comparatively few, it was not to be won- 

 dered that practice was very defective. 

 It must, however, be observed, that if the 

 earlier apparatus were mostly deficient in 

 the quantity of pipe employed, many of 

 those more recently erected err in the 

 opposite extreme. The error arises not 

 from any defect in the data or in the cal- 

 culations, but from assuming, as the 

 minimum of external air, a temperature 

 which very rarely occurs in this country, 

 and which lasts for so very short a time 

 that no building has time to cool down 

 to a corresponding temperature. 



" The next point which requires notice 

 is the expediency of heating several 

 houses from the same boiler. Now, to 

 this arrangement there is not the slightest 

 objection, provided the same number or 

 extent of houses is always to be heated at 

 the same time — that is to say, several 

 hothouses, all of which require permanent 

 heat, but different temperatures, may be 

 advantageously heated from one boiler. 

 In like manner a range of greenhouses 

 always requiring heat at the same time, 

 to exclude frost, may be worked from one 

 boiler, though different degrees of heat 

 are required in them ; and even if one of 

 these sometimes requires, as it probably 

 would, a slight degree of heat when the 

 others require none, this may be arranged 

 without difficulty or inconvenience. But 

 serious inconveniences will arise from 

 any attempt to heat two buildings, in one 

 of which occasional, and in the other per- 

 manent, heat is required; and this in- 

 convenience will be great in proportion 

 to the size of the buildings, especially if, 

 as is generally the case, the hothouse is 

 small, and the greenhouse or pits more 

 extensive. The same inconvenience will 

 also be felt if two vineries, one to be 

 forced at a later period than the other, 

 are to be heated from one boiler. The 

 reason is briefly this, that the capacity of 

 the furnace for fuel, the area of its bars 

 or its consuming power, and the boiler- 



surface or absorbing power, are all calcu- 

 lated with reference to a certain quantity 

 of pipe ; by urging the fire to the utmost 

 power which is consistent with a proper 

 duration of its heat, the pipes to which it 

 is ordinarily attached are heated to their 

 maximum, and the maximum heat is 

 produced as required in the building. If, 

 at this time, an additional extent of duty 

 is laid on the boiler, by opening the 

 sluices which connect it with the pipes 

 of a greenhouse or pits, the temperature of 

 the ordinary service-pipes is reduced, and 

 the hothouse receives a diminished quan- 

 tity of heat just when it requires most. 

 On' the other hand, if the common boiler 

 be constructed of a size and power ade- 

 quate to the double service, it will, when 

 applied to the hothouse only, constantly 

 overheat it ; and this effect can be pre- 

 vented only by throwing open the furnace 

 door, and allowing the fuel to burn to 

 waste ; — for, be it observed, it is the area 

 of the furnace bars which regulates the 

 consumption of fuel. It is true that, by 

 means of dampers and skilful manage- 

 ment, some remedy may be found for 

 these evils; but, nevertheless, they will 

 exist to a greater or less extent, and the 

 arrangement above mentioned should 

 never be willingly adopted. 



" The different temperature of stoves to 

 be heated from the same boiler may be 

 regulated with the most philosophic accu- 

 racy, by allotting to each house quantities 

 of pipe bearing a different proportion to 

 their respective surfaces of glass. The 

 difference thus established will be main- 

 tained for all temperatures, unless acci- 

 dental circumstances of exposure to wind 

 or imperfect glazing should cause a varia- 

 tion, and the general heat of all may be 

 regulated by attention to one fire." 



Hitherto, for the most part, hothouses 

 have been heated by pipes laid in a hori- 

 zontal direction, and generally running 

 parallel to the ends and front of the 

 house ; and in nine cases out of ten the 

 extent of piping has been far too limited 

 to effect the purpose required, or to take 

 the heat from the boiler so fast as it is 

 generated : hence an enormous waste of 

 fuel is constantly going on. Where it is 

 inconvenient to add to the number of 

 pipes, radiators may be attached to them, 

 or coils of smaller pipes may be placed in 

 convenient parts of the house, either in 



