AVIARIES, BIRD- ROOMS AND CAGES. 



47 



Ventilation means simply the changing of the foul, 

 used-up air of a building for the pure fresh outside 

 element. We must remember that whenever we admit 

 cold air into a room where a higher temperature exists, 

 it naturally sinks to the floor, so that by admitting the 

 necessary pure element somewhere near the ceiling we 

 get it into the room in such a way that it must gradually 

 sink and thus create a free circulation. At the same 

 time we must provide an outlet for the used-up gases, 

 and as this foul air rises naturally to the top of the build- 

 ing, we must make the outlet at the same place. By 

 carrying out this principle we get a free circulation 

 and consequent change of air, and without the fatal 

 draught we wish to avoid. If fresh air were admitted 

 into the building at the bottom, we should by that 

 means get such an inrush that it would be a straight 

 drive out of the/ Ventilator at the top. This would 

 naturally create a violent current which would probably 

 cut short our efforts at cage-bird keeping. 



Fig. 26 shows a 

 simple plan of ventila- 

 tion. The fresh air 

 enters the building at 

 A, sinks to the floor,, 

 rises again when 

 warmed, and passes ,out 

 of the building at the 

 ventilator B. This 

 system is splendid for 

 buildings erected out- 

 side, but for indoor 

 rooms, where most 

 fanciers keep their pets, 

 it requires a slight al- 

 teration. In ! that case 

 the air should be ad- 

 mitted at the window; 

 and an outlet be pro- 

 vided by removing a 

 brick in the chimney 



\ 



Fig. 26. System of Ventilation. 



near the ceiling. The window may be pulled down 

 a few inches and a piece of perforated zinc be 

 nailed over the opening, or a block of wood slipped 



