VROM DIFFERENT APFAHATI B. 



as the cold air, thus admitted, is very annoying in its passage to 

 the fire-place, and particularly to those seated mar (lie doors or 

 window-;. Now, these inconveniences may be entirelj avoided, 

 and all parts of the room rendered equally i ifortable, bj fur- 

 bishing the room, as is now done in some instances, with a 

 supply pipe mar the lire-place, for the admission of air. In 

 this pipe there should lira valve, to regulate the quantity of air 

 necessary to be admitted, by which the pressure of the externa] 

 air. at the joints, or nv\ ices, may not only be wholly taken off, 

 but an outward current produced, through the crevices at the 

 higher parts of the room. 



The objection which has been made to this manner of ad- 

 mitting the air, that it does not change the air in the room 

 sufficiently for respiration, appears to be gratuitous, and has 

 been disproved by experience, in rooms of ordinary size, when 

 not unusually crowded. 



An additional improvement, to obviate the inconvenience 

 experienced by over-heated or crowded rooms, would be to 

 furnish a ventilator in the chimney, near the ceiling; but tin 

 most rational plan, in these eases, would be to remove the cans, 

 by diminishing the lire. 



Having shown very (dearly, during the preceding remarks, 

 that the reason why a combustible burns better at one timi 

 than another, cannot be owing to an\ change in the veloeitj 

 of the current within a chimney, in consequence "I chan| 

 in the pressure of the atmosphere, it becomes obligatory on mi 

 ;«s an objector to this opinion, to assign a more satisfactory 

 cause. 



The fact that combustible bodies generally hum better, 

 when the barometer is at m. than when it is at J s inch 

 other things being equal, is admitted. The principal causi ot 

 this, appears to be, that the air is generally drier, and bettei 

 adapted to produce rapid combustion, having less aqueous 

 vapour mechanically mixed with it. Now moist air n tarda 

 combustion, and cools the burning body, more than dry air. 

 because it posa m sa greater capacity for hi at, and. consequently 

 requires more from the burning bodj to raise its U mp ratun 



