SCHOOL HYGIENE 427 



should be enough windows to provide sufficient light during 

 this season, as well as on cloudy days. 



The direction from which the light comes is a second point 

 to consider. It should not come from the front, because 

 it would then shine directly into the children's eyes, and 

 strain them. It should not come from the rear because the 

 shadow of the body would be thrown on the desk. It should 

 not come from the right because the shadow of the hand is 

 thrown on the reading and writing. The best arrangement 

 is to have the light come from the left. 



The bottom of the window should be at such a height that 

 it is above the level of the eyes of the children when they are 

 seated. This should be from three and one-half to four feet. 

 If it is lower than this, it strains the eyes more because the 

 light shines directly into them. The top of the window 

 should reach up well toward the ceiling, as the light from 

 high up is better distributed throughout the room. 



Heating and ventilating the building. The general prin- 

 ciples involved in heating and ventilating the school build- 

 ing are the same as those involved in the home, which were 

 discussed in the first and second chapters. But in the 

 schoolroom more attention should be given to ventilation 

 than is ordinarily done in the home, because a larger number 

 of persons are gathered in one room. 



Essentials of ventilation. As we have seen in Chapter II, 

 good ventilation requires attention to the following matters ; 

 a constant supply of fresh air, a motion of air, the right de- 

 gree of temperature, and the right per cent of humidity. 



Fresh air and motion. To keep a constant supply of fresh 

 air requires two openings in a room, an inlet where the fresh 

 air enters and an outlet where the used air is removed. 

 Experiments which have been carried on show that the 

 best place for the inlet is about eight or nine feet from the 

 floor and that the best place for the outlet is within a foot 

 of the floor and on the same side of the room as the inlet. 



