VENTILATION BY OPEN FIREPLACES. 339 



once by the fact that such air being colder than that of the 

 room, it must fall immediately it enters. The rivulet 

 under the door is thus supplemented by cascades pouring 

 down from the top and sides of the door and the top and 

 sides of the windows, all being tributaries to the lake of 

 cold air covering the floor. 



The next question to be considered is, what is the depth 

 of this lake? In this, as in every other such accumulation 

 of either air or water, the level of the upper surface of the 

 lake is determined by that of its outlet. The outlet in 

 this case is the chimney hole, through which all the over- 

 flow pours upwards; and, therefore, the surface of the 

 flowing stratum of cold air corresponds with the upper part 

 of the chimney hole, or of the register, where register stoves 

 are used. 



Below this level there is abundant ventilation, above it 

 there is none. The cat that sits on the hearth-rug has an 

 abundant supply of fresh air, and if we had trachea! breath- 

 ing apertures all down the sides of our bodies, as caterpil- 

 lars have, those on our lower extremities might enjoy the 

 ventilation. If we squatted on the ground like savages 

 something might be said for the fire-hole ventilator. But 

 as we are addicted to sitting on chairs that raise our breath- 

 ing apparatus considerably above the level of the top of the 

 register, the maximum efficiency of the flow of cold air in 

 the lake below is expressed by the prevalence of chilblains 

 and rheumatism.* 



The atmosphere in which our heads are immersed is 

 practically stagnant; the radiations from the fire, plus the 

 animal heat from our bodies, just warm it sufficiently to 

 enable the cool entering air to push it upwards above the 

 chimney outlet and the surface of the lower moving stra- 

 tum, and to keep it there in a condition of stagnation. 



If anybody doubts the correctness of this description, ho 

 has only to sit in an ordinary English room where a good 

 fire is burning the doors and windows closed, as usual 



* Since the above was written, a correspondent in Paris tells me 

 that a caricature exists, representing a Frenchman enjoying an open 

 fire by standing on his head in the middle of the room. 



