348 



Our Surroundings 



attention is given to the temperature and to the regulation of the 

 amount of moisture present. 



Methods of Ventilation. The simplest way to ventilate a 

 room is by opening the windows, both at the top and bottom, 



Brown Brothers. 



A WARNING OF INVISIBLE DANGER 



A canary is extremely sensitive to foul air. If there are poisonous gases in a mine 

 the bird will quickly die, warning the miners that they are in danger. 



thus allowing free circulation of air. This method, however, can 

 be used with safety and comfort only in warm weather. Even 

 ther "t is wise to prevent direct drafts by placing a window board 



