212 FIXED STRUCTURES FOR GROWING 



below, little or no heat escapes by the chimney, the whole being taken up by 

 the surrounding water. The economy, therefore, of fuel in such an apparatus 

 is very great : and it is also evident that excess of draught must be carefully 

 guarded against, so much only being allowed as will consume the fuel 

 steadily, which is easily learned by experience. The necessity, also, of keeping 

 the aperture in front close, so that air enters the furnace only through the ash- 

 pit, is hence evident. The water, it will be observed, is in close and immediate 

 contact with the red-hot fuel on all sides, no black smoking coals intervening, 

 as in most kinds of boilers ; hence the great power in proportion to their size. 

 Economy of fuel is not, however, the sole or principal advantage of these 

 boilers ; their great recommendation is the long duration of steady heat which 

 they insure without attendance. When properly managed, they may be 

 depended upon for maintaining heat twelve hours untouched. This to many 

 amateurs, who do not command the services of a resident gardener, is invalu- 

 able. In the next place, they are applicable to houses and pits on the 

 smallest possible scale ; a three-light pit may be kept at a temperature as 

 uniform as that of the largest hothouse, without any trouble by night. It 

 was for a purpose of this kind that Mr. Rogers was originally led to devise 

 them, and he has for three years past cultivated Orchideae in a small house 

 not twelve feet square in this manner. Mr. Rogers's gardener does not live 

 on the premises ; and the temperature, as ascertained by a double self-regis- 

 tering thermometer, rarely varies 6 during the night. 



It is to be observed, that, as the quantity of heat produced depends upon 

 the quantity of fuel consumed, each boiler must contain, at one charge, fuel 

 sufficient to supply the pipes to which it is attached with heat for twelve 

 hours ; it is therefore necessary that the size of the boilers be proportioned to 

 the work they have to do. They are cast in the following sizes, which have 

 been found most generally useful : 



10 -inch furnace, working 40 ft. to 60 ft. 4-inch pipe, price 4 10s. 

 13-inch do. do. 60ft. to 120 ft. do. price 6 Os. 

 15-inch do. do. 120 ft. to 200 ft. do. price 7 10s.* 



Where the quantity of pipe exceeds the above amount, two boilers have 

 hitherto been employed ; but there is no reason why an eighteen-inch should 

 not be cast, if a sufficient demand arose for them ; boilers of this size have 

 been found very effective in copper ; and a twenty- one inch, cast in iron for Mr. 

 Wilmot of Isleworth, worked exceedingly well. The numbers affixed to the 

 boilers above are such as they will work properly and efficiently at all times. 

 Some boilers of the above dimensions have been found to do a good deal more 

 work than is here allotted to them ; but this has only been by increasing the 

 draught, and producing more intense combustion, a great deal of heat at the 

 same time escaping by the chimney. When thus employed, the peculiar 

 advantages of these boilers are lost; fuel is burnt to waste, and consumed so 

 rapidly that they do not maintain their heat as long as is desirable. Duration 

 of heat and economy of fuel are considered by Mr. Rogers as paramount objects. 



The only case in which stronger draught may be allowed is where the fire 

 works into a flue in the house : but the objection of the rapid consumption of 

 fuel is not thus removed ; nor can this arrangement be generally recom- 



* The fittings, comprising doors, dampers, &c., all things, in short, peculiar to the appa- 

 ratus as above described, vary from U. 5s. to U. 15s., according to the size, and the 

 articles required. The appendages for steaming the house are not included in this estimate. 



