326 SCIENCE OF GARDENING. PART II. 



Hart, Trans, vol. iv.) The furnaces from whence the flues proceed, are generally 

 placed behind the back wall, as being unsightly objects ; but in point of utility, the best 

 situation is at the end of the front wall, so as it may enter the house, and proceed a con- 

 siderable length without making an angle. A greater utility, however, is here given up 

 for fitness ; it being more fitting in a gentleman's garden that something should be sa- 

 crificed to neatness, than that all should be sacrificed to profit. 



.1661. The direction of flues, in general, is round the house, commencing always within 

 a short distance of the parapet, and after making the course of three sides, that is, of the 

 end at which the fire enters, of the front, and of the opposite end, it returns (in narrow 

 houses) near to or in the back wall, or (in wide houses) up the middle, forming a path ; 

 and in others, immediately over or along side of the first course. In all narrow houses 

 this last is the best mode. 



1662. The power of flues depends so much on their construction, the kind of fuel, the 

 roof, mode of glazing, &c. that very little can be affirmed with any degree of certainty on 

 this subject ; 3000 cubic feet of air is in general enough for one fire to command in stoves 

 or forcing-houses ; and 5000 in lean-to green-houses. In houses exposed on all sides, 

 2000 cubic feet is enough in stoves, and 3000 cubic feet for green-houses. The safest 

 side on which to err is rather to attach too little than too much extent to each fire, as ex- 

 cessive fires generally force through the flues some smoke or mephitic air ; and besides 

 produce too much heat at that part of the house where the flue enters. 



1663. Dampers, or valves, are useful in flues and chimneys, both in case of accident and 

 also to moderate the heat, or in case of one furnace supplying two flues, to regulate the 

 passage of smoke and heat. For general purposes, however, the ash-pit door is perfectly 

 sufficient. The damper, and furnace, and ash-pit doors ought seldom to be all shut 

 at the same time, as such a confinement of the hot air of the flue is apt, owing to its ex- 

 pansion by increased heat from the hot masonry, to force some of it through the joints of 

 the flue into the house. 



1664. Chimney-tops are generally built on the coping of the back wall, and some- 

 times ornamented with mouldings, and even disguised as vases. Where there are 

 only one or two to a conservatory or other house of ornament, these last modes may 

 be allowable ; but in culinary ranges, it appears to us an unsuitable application of orna- 

 ment either to form on the stone or brick chimneys many mouldings, or to disguise them, 

 as urns or vases. When these last are to be adopted, cast-iron presents abundant facilities 

 of economical execution. There is a four-sided composition -stone chimney-pot recently 

 come into use near London, which will answer extremely well till it becomes so common 

 as to be reckoned vulgar. Sometimes the flues are carried under ground to some 

 distance from the hot-house, and the chimney carried up in a group of trees, or other- 

 wise concealed. This practice is suitable to detached buildings formed of glass on all 

 sides. 



SUBSECT. 7. Steam Boilers and Tubes. 



1 665. Steam affords the most simple and effectual mode of heating hot-houses, and indeed 

 large bodies of air in every description of chamber, for no other fluid is found so con- 

 venient a carrier of heat. The heat given out by vapor, differs in nothing from that given 

 out by smoke, though an idea to the contrary prevails among gardeners, from the cir- 

 cumstances of some foul air escaping into the house from the flues, especially if these are 

 over-heated or over- watered ; and from some vapor issuing from the steam -tubes when 

 these are not perfectly secure at the joints. Hence flues are said to produce a burnt or 

 drying heat, and steam-tubes a moist or genial heat, and in a popular sense this is cor- 

 rect for the reasons stated. It is not, however, the genial nature of steam heat which 

 is its chief recommendation for plant-habitations, but the equality of its distribution, 

 and the distance to which it may be carried. Steam can never heat the tubes, even close 

 to the boiler, above 212 degrees, and it will heat them to the same degree, or nearly so, at 

 the distance of 1000, 2000, or an indefinite number of feet. Hence results the convenience 

 of heating any range or assemblage of hot-houses, however great, from one boiler, and the 

 lessened risk of over or insufficient heating at whatever distance the house may be from 

 the fire-place. The secondary advantages of heating by steam are the saving of fuel and 

 labor, and the neatness and compactness of the whole apparatus. Instead of a gardener 

 having to attend to a dozen or more fires, he has only to attend to one ; instead of ashes, 

 and coal, and unsightly objects at a dozen or more places in a garden, they are limited to 

 one place ; and instead of twelve paltry chimney-tops, there is only one, which being 

 necessarily large and high, may be finished as a pillar so as to have effect as an object ; 

 instead of twelve vomitors of smoke and flakes of soot, the smoke may be burned by 

 using Parkes's or some other smoke-consuming furnace. The steam-tubes occupy much 

 less space in the house than flues, and require no cleaning ; they may often pass under 

 paths where flues would extend too deep ; there is no danger of steam not drawing or 

 circulating freely as is often the case with flues, and always when they are too narrow or 



