DOMESTIC VENTILATION. 343 



house thus ventilated has some hundreds of small, very low- 

 roofed rooms, and a system of passages or corridors with an 

 united length of many miles, and that its inhabitants count 

 by hundreds. 



Such dwellings being thus ventilated and rendered habit- 

 able for man and beast, it is idle to dispute the practical 

 possibility 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 simply and skil- 

 fully controlling and directing the natural movements of 

 unequally-heated volumes of air. Complex mechanical 

 devices for forcing the ventilation by means of gigantic fan- 

 wheels, etc., or by steam- jets, have been tried, and are now 

 generally abandoned. An inlet and an outlet are provided, 

 and no air is allowed to pass inwards or outwards 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 

 mine the coal on a certain estate. We first ascertain the 

 "dip" of the seam, or its deviation from horizontality, and 

 then start at the lowest part, not, as some suppose, at that 

 part nearest to the surface. The reason for this is obvious 

 on a little reflection, 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 upwards, we can at once form a ' ' sumpf," 

 or bottom receptacle, to receive the drainage, and from 

 which the accumulated water may be pumped. This, how- 

 ever, is only by the way, and not directly connected with 

 our main subject, the ventilation. 



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

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

 convenient distance from each other. If they are deep, it 

 becomes necessary to '.eminence ventilation of the mere 

 shafts themselves ;n the Bourse of sinking. This is done 



