Transactions of the London Horticultural Society. 427 



possible exception is in the case of forcing-housesTor very early grapes ; and it 

 is very doubtful whether, even here, any good would be attained by greater 

 power. I am aware that it is urged that it is always easy to work an 

 apparatus below its power, and that such an arrangement is economical 

 of fuel; and within certain limits this is undoubtedly true : but, if the quantity 

 of pipe materially exceeds what is necessary, the only means of keeping the 

 house at a moderate temperature is by leaving the furnace door open, and a 

 very great waste, instead of any economy of fuel, necessarily results. The 

 simplest remedy for this defect is to encase some portion of the pipes either 

 with sand or sawdust, which prevents the heat from escaping into the house, 

 by diminishing the radiating surface. 



" 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 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 part, 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 need none, this may be arranged without difficulty or 

 inconvenience : but serious inconvenience will arise from any attempt to heat 

 two buildings, in one of which occasional and in the other permanent heat is 

 required ; and this inconvenience will be great in proportion to the size of the 

 buildings, especially, if, as is generally the case, the hothouse is small and 

 the greenhouses 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 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 calculated with reference to a certain 

 quantity of pipe, by urging the fire to its 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 to 

 the boiler, by opening the sluices which connect it with the pipes of a green- 

 house or pits, the temperature of the ordinary service pipes is reduced, and 

 the hothouse receives a diminished quantity of heat just when it requires 

 most. On the other hand, if the common boiler be constructed of a size and 

 power adequate to the double service, it will, when applied to the hothouse 

 only, constantly overheat it, and this effect can be prevented 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 management 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 

 willingly be adopted. 



" The different temperature of stoves, to be heated from the same boiler, 

 may be regulated with the most philosophical accuracy, by allotting to each 

 house quantities of pipe bearing a different proportion to their respective 

 surfaces of glass ; the difference thus established will be maintained for 

 all temperatures, unless accidental cirucmstances of exposure to wind, or 

 imperfect glazing, should cause a variation, and the general heat of all may be 

 regulated by attention to one fire. 



" Closely connected with the subject of heating is the providing an adequate 

 degree of moisture in the atmosphere heated ; indeed it is upon this, above 

 every thing else, that the perfection or imperfection of an artificial climate 

 depends ; and it is by no means one of the least advantages of hot water 

 pipes, that they do not, like brick flues, dry the atmosphere by absorbing its 

 moisture. But this negative advantage falls far short of what is necessary. 

 The air of all buildings artificially heated is dried by condensation upon the 



