DOMESTIC VENTILATION. 65 



Imagine your dwelling-house buried a quarter of a mile of 

 perpendicular depth below the surface of the earth, and its walls 

 giving off suffocating* and explosive gases in such quantities 

 that steady and abundant ventilation shall be a matter of life 

 or death, and that in spite of this it is made so far habitable 

 that men who spend half their days there retain robust health 

 and live to green old age, and that horses, after remaining there- 

 day and night for many months, actually improve in condition. 

 Imagine, further, that the house thus ventilated has some 

 hundreds of small, very low-roofed rooms, and a system of 

 passages or corridors with a united length of many miles, 

 and that its inhabitants count by hundreds. 



Such dwellings being thus ventilated and rendered habi- 

 table for man and beast, it is idle to dispute the practical possi- 

 bility of supplying fresh air of any given temperature to a 

 mere box of brick or stone, standing in the midst of the 

 atmosphere, and containing but a few passages and apartments. 



The problem is solved in the coal-pit by simple and skilfully 

 controlling and directing the natural movements of unequally 

 heated volumes of air. Complex mechanical t devices for forc- 

 ing the ventilation by means of gigantic fan- wheels, etc., < 

 by steam-jets, have been tried, and are now generally aban- 

 doned. An inlet and an outlet are provided, and no air is 

 allowed to pass inward or outward by any other course than 

 that which has been pre-arranged for the purposes of efficient 

 ventilation. I place especial emphasis on this condition, 

 believing that its systematic violation is the primary cause of 

 the bungling muddle of our domestic ventilation. 



Let us suppose that we are going to open a coal-pit to win 

 the coal on a certain estate. We first ascertain the " dip" 

 of the seam, or its deviation from horizontality, and then start 

 at the loioest part, not, as some suppose, at that part nearest 

 to the surface. The reason for this is obvious on a little reflec- 

 tion, for if we began at the shallowest part of an ordinary 

 water-bearing stratum we should have to drive down under 

 water ; but, by beginning at the lowest part and driving up- 

 ward, we can at once form a " surapf " or bottom receptacle, 

 to receive the drainage, and from which the accumulated 

 water may be pumped. This, however, is only by the way, 

 and not directly connected with our main subject, the venti- 

 lation. 



In order to secure this, the modern practice is to sink two 

 pits, " a pair," as they are called, side by side, at any con- 



