invented hy John Rogers, Jan., Esq. 137 



throat of the furnace, when it will last through the night. In 

 filling, care, of course, must be taken that the fuel is not so small 

 and dusty as to stop the draught. Where cinders are used they 

 should be well sifted. The proper management of these boilers 

 may be best secured by explaining the principle upon which they 

 are constructed. As fuel cannot be consumed without air, if a 

 furnace be constructed of considerable depth, and filled with fuel, 

 and air be admitted only at the bottom, that fuel alone is con- 

 sumed which lies immediately on the bars, and first receives the 

 draught of air. The fuel above, provided it transmits the air, 

 becomes red-hot, or nearly so, but does not consume until that 

 below it is destroyed. In this manner, one of these conical 

 furnaces being lighted and filled with fuel, that portion in the 

 upper part of the furnace which cannot burn absorbs the heat 

 of the burning fuel below, and radiates or transmits it to the 

 water on every side. So perfect is this absorption of heat, 

 that for several hours after the furnace has been filled up with 

 cinders, though there may be a fierce fire 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 ad- 

 vantage 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 main- 

 taining heat 12 hours untouched. This to many amateurs, who 

 do not command the services of a resident gardener, is invaluable. 

 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 hot-house, without 

 any trouble by night. It was for a purpose of this kind that I 

 was originally led to devise them, and I have for three years past 

 cultivated Orchideae in a small house not 1 2 ft. square in this 

 manner. My gardener does not live on the premises ; and the 

 temperature, as ascertained by a double self-registering ther- 

 mometer, rarely varies 5° during the night. 



It is to be observed, that, as the quantity of heat produced de- 

 pends upon the quantity of fuel consumed, each boiler must 

 contain, at one charge, fuel sufficient to supply the pipes to 



1840. March. l 



