VENTILATION. 233 



removed by placing a register (which may be closed or 

 opened at pleasure) at a, in the upper corner, so that 

 the confined air may escape into the chimney. With- 

 out this provision, it is nearly impossible to preserve 

 the air in proper condition for breathing, for the upper 

 part, being warmest and lightest, remains unchanged 

 at the top. In rooms heated by stoves, registers for es- 

 cape of the foul air are still more important, where the 

 thermometer frequently indicates twenty degrees differ- 

 ence in the heat above and at the floor, the lower stra- 

 tum of air resting like a cold lake about the feet, while 

 the head is heated unduly. 



"When the draught of the chimney-fire is not strong, 

 the smoke may, however, escape through the ventilat- 

 ing register into the room. To avoid this difficulty, it 

 is best to provide separate air-flues in the walls when 

 the house is built, for effecting perfect ventilation. In 

 rooms strongly heated by fires, the fresh air should be 

 admitted near the ceiHng, producing descending cur- 

 rents, and effecting a complete circulation in the air of 

 the room. But in sleeping apartments and in closets, 

 not heated artificially, and where the descending cur- 

 rents will not take place, the fresh air should be admit- 

 ted through a register or small rolling blind near the 

 floor, and discharged near the ceiling into an air-flue. 

 Fig. 197. The excessive warmth of 



garrets in mid-summer may be 

 avoided by placing a ventilator 

 at the highest part, and admit- 

 ting air at windows or openmgs 

 near the eaves {Fig-. 197), thus 



Mode of Ventilating Garrets. SWecpUlg aU thc hot air OUt by 



