426 Transactions of the London Horticultural Society. 



objects within the building, which is gradually transmitted by the roof, so that, 

 in fact, the necessity for rapid heating, even in greenhouses, is really less than 

 at first sight appears. 



" The real desideratum is a furnace so constructed that it shall contain 

 fuel enough to supply the pipes with as much heat as they can radiate during 

 the night, and which may be depended upon for burning steadily and perfectly 

 whatever fuel is put into it. Not with that accurate precision requisite where 

 the temperature of the house depends upon the exact amount of combustion 

 per hour, but sufficiently slowly to allow the water to absorb the greatest 

 possible portion of the heat generated. With such an apparatus, the fire 

 being once effectually lighted, the gardener need be under no apprehension 

 that the heat during the night will prove insufficient, though it may be several 

 hours before the pipes attain their maximum temperature. 



" I have dwelt somewhat at large on this point, because it is one on which 

 much mistake exists, and under this misapprehension the best apparatus may 

 be condemned as defective, and a very imperfect one preferred and adopted in 

 its stead ; that which is commonly adopted as a criterion of excellence 

 being really a proof of defective construction. 



" There can be on the whole no doubt that three-inch or four-inch pipes 

 are exceedingly preferable to smaller ones, where economy of fuel and uniform 

 adjustment of the temperature for several hours are the primary objects. 

 Where ornament or great economy of space is important, and economy of 

 fuel is not much considered, smaller pipes may be employed : but, where rapid 

 heating is considered essential, 1 believe it will be found best to have recourse 

 to the old expedient of brick flues ; and their attendant inconveniences must 

 be considered as the price paid for this advantage, real or imaginary. The 

 most perfect construction of these has been so fully canvassed in the earlier 

 volumes of the Horticultural Trcmsactions y that it is unnecessary here to 

 enlarge upon it. 



" The next point to be noticed is the absolute amount of heat produced 

 by any hot-water apparatus, which depends upon the proportion between the 

 surface of pipe and surface of external glass in the building. The laws both 

 of cooling by the glass and of radiation from the pipes have been so ably and 

 accurately treated by Mr. Charles Hood in his most valuable treatise on hot- 

 water apparatus, that there is now nothing to desire on this head. An 

 apparatus may be adjusted with the most minute accuracy to the work re- 

 quired of it. Formerly the most preposterous blunders were committed on 

 this point. Almost all the earlier apparatus are incompetent to the work 

 required of them, the quantity of pipe being utterly insufficient to produce 

 the heat desired, while, the boiler being large and of very defective con- 

 struction, a vast quantity of fuel was burnt to waste : the gardener finding 

 his heat deficient naturally stokes up his fire and throws on fuel in the hope 

 of increasing it ; but the only result of his labour is the more rapid de- 

 struction of the boiler itself. Until the publication of Mr. Hood's work 

 above-mentioned, the principle of circulation in hot-water apparatus was 

 very little understood, most erroneous notions prevailed on the subject ; and, 

 where the principles were unknown and opportunities of experiment com- 

 paratively few, it was not to be wondered 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 calculations, but from assuming, as the minimum of ex- 

 ternal 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 gardener is generally consulted as to the 

 heat he requires, and if he states, as he probably may do, that he wishes to 

 keep his greenhouse at 50° and his stove at 65° when outer air is 5° 

 or 0°, the apparatus is constructed accordingly, and will of course be found 

 excessive in power; a power of 30° for greenhouses and of 45° for hothouses 

 .will, I believe, be found ample under any circumstances in England ; the only 



