PRELIMINARY REMARKS. 



143 



nearly two-thirds of the whole effect. The 

 experiments of Hood prove that " 1 square 

 foot of glass will cool 1.279 cubic feet of 

 air as many degrees per minute as the 

 internal temperature of the house exceeds 

 that of the external air : that is, if the 

 difference between the internal and ex- 

 ternal temperature of the house be 30°, 

 then 1.279 cubic feet of air will be cooled 

 30° by each square foot of glass; or, more 

 correctly, as much heat as is equal to this 

 will be given off by each square foot of 

 glass." This calculation is taken, pre- 

 suming the air externally to be still, but 

 in high winds the loss of heat will be 

 much greater ; hence houses placed in 

 exposed situations are more difficult to 

 heat than such as are more sheltered. 



In estimating the extent of radiation 

 in glass houses, it will be found sufficiently 

 accurate for ordinary purposes to take 

 the whole surface of the sashes, and de- 

 duct one-eighth of the amount for the 

 wood-work ; for in hothouses, where glass 

 of a small size, say 6 inches by 4, or 6 by 

 8, is used, the surface of the astragals 

 and rails fully amounts to this quantity; 

 but in roofs without framed sashes, and 

 having glass 9 to 12 inches broad, the 

 amount to be deducted will be much less; 

 and in the case of metallic houses, as the 

 radiation will be quite as much from the 

 metal as from the glass, no deduction 

 whatever must be made. 



Heating upon scientific principles, even 

 as regards dwelling-houses, was very little 

 understood in this country until the ar- 

 rival of Count Rumford, who gave an 

 impetus to it by the publication of his 

 essays, and the production of the grates 

 known by his name. The late Walter 

 Nicol and John C. Loudon were amongst 

 the first who effected improvements in 

 heating hothouses, and both began at the 

 right end, by constructing improved fur- 

 naces. Hay and Stewart also directed 

 their attention to this matter; but, so far 

 as we can learn, it was Count Rumford 

 and Dr Black who first used double fur- 

 nace-doors and ash-pit registers, and these, 

 with slight modifications, have remained 

 in use ever since. The utility of double 

 doors is obvious. They are not only more 

 durable, but they also keep in the heat, 

 and prevent a current of cold air from 

 entering into the furnace, and of course 

 passing rapidly over the fire, so as to be 



less capable of heating the flue or boiler 

 than that air which is admitted through 

 the ash-pit register, and has to pass 

 through the fire before it enters the flue. 

 The supply of air is also graduated by 

 being admitted through the ash-pit door, 

 this securing a more steady combustion. 



In 1805, the late Mr Loudon published 

 " A Treatise on Improvements in Hot- 

 houses," one of the earliest productions of 

 that eminent man, who during his life did 

 so much for the advancement of horticul- 

 ture. In that work he describes an improved 

 furnace and flue, which, although it has 

 been condemned by many, and ourselves 

 amongst the number, still, upon more 

 mature deliberation, we now admit to have 

 certain merits. The intention of the 

 author appears to have been to econo- 

 mise fuel, by collecting heated air above 

 and around the furnace, and so bringing 

 it into the house. This is the foundation 

 of all improvements in heating ; for it is 

 beyond a doubt, that not one-half of the 

 heat produced by the fuel in most furnaces 

 is directed to the object intended, chiefly 

 in consequence of the bad construction of 

 the furnaces, by which an unnecessary 

 quantity of air is admitted, tending to 

 hasten the consumption of the fuel, and 

 drive the heated air rapidly through the 

 flues and out at the chimney top, accom- 

 panied with volumes of smoke and an 

 immense quantity of unconsumed car- 

 bonaceous matter, most of which ought 

 to have been consumed, and to have 

 afforded its quota of heat. Experiments 

 have been made, which prove that the loss 

 of heat by this latter waste is as 975 to 

 1160. 



The great objection to the admission 

 of heated air into houses by such means, 

 is the introduction of noxious gases, con- 

 sisting of sulphuretted, phosphorated, and 

 carburetted hydrogen, besides various 

 compounds of nitrogen and carbon, all of 

 which are highly injurious to both animal 

 and vegetable life. Certainly these effects 

 are not so great where the air is heated 

 by passing over bricks only ; but no hot- 

 air furnace exists without a portion of 

 metallic material being used in its con- 

 struction; and hence the difficulty of 

 applying the heat generated above and 

 around most furnaces to the greatest 

 advantage, and at the least possible risk of 

 deteriorating the atmosphere to be heated. 



