^6*6 Mr Tredgold on (he Princi'ples and Practiee 
In these rules, the fire is estimated to be capable of ' keeping' 
the temperature of the room 30° above that of the external air, 
when it is supplied with Newcastle coal ; and the fire being ren- 
dered capable of regulation bj a damper in the chimney, and a 
register at the ash-pit, it is easy to have any variation of heat 
within that range. 
In churches, and buildings of a like kind, the whole of the 
air, or nearly the whole, may be supplied to the stove frona 
within the building ; but, in smaller buildings that are in more 
frequent use, a part of the air should be brought from the ex- 
terior, and the rest from the interior ; the relative proportions of 
which will be determined by what has been remarked in treating 
the subject of ventilation. 
Enough has, perhaps, been said respecting the properties and 
powers of stoves of this kind ; and if the importance of the prin- 
ciples of limiting the temperature of the surface, and of prevent- 
ing the heated air becoming charged with minute particles of 
dust be admitted, it must be acknowledged, that very few of the 
contrivances called Stoves, are proper instruments for aifording 
heat. 
About the year 1196, a new method of limiting the tempera- 
ture of a surface, for affording heat, was discovered by Messrs 
Strutt of Derby. It consists in placing the surface at such a 
distance from the fire, that its temperature cannot exceed 300® ; 
and as, from the nature of the arrangement, this surface can on- 
ly be of small extent, it was found necessary to direct the air in 
small streams against the heated surface with great velocity, to 
cause it to absorb a greater quantity of beat, and by that means, 
compensate for want of surface. 
It will be obvious, that, in this arrangement, the fire should 
either be raised in an open grate in the centre of the cocMe (for 
that is the name given to the vessel which is heated), or the fire 
should give offbeat through sides of slow conducting matter;— 
the latter appears to be the plan adopted by Messrs Strutt. It 
will also be evident, that the smoke of the chimney cannot be 
brought to a lower temperature than that of the surface giving 
off heat, unless it be given off through the sides of the flue 
which conducts it to the chimney. Consequently, the whole of 
the heat cannot be obtained without in part employing the prin- 
