Page:Popular Science Monthly Volume 16.djvu/544

518 are manifested. The diminution of light goes on almost unnoticed by well-formed eyes, for it is compensated by the increase of the used surface of the cornea. Less perfect eyes, on the other hand, not being able to perform their functions with ease, have to make fatiguing efforts to accommodate themselves to the situation, which tend to increase existing defects or to induce short-sightedness.

Adults are less liable than children to suffer injury from insufficient light, for several reasons: 1. Their pupils being less dilatable, they are obliged to desist from their work sooner when the light diminishes; 2. They make more frequent use of glasses; 3. They are less often confined, like school-children, and compelled to continue their labors after the light has become insufficient; and, 4. The coverings of their eyes are less extensible, and, if they have so far escaped myopia, they have more chances of continuing free from it.

A good management of the daylight is especially important with regard to the construction of schoolhouses. It is not enough to lay down a rule establishing the proportion which the surface of glass should bear to the number of pupils; attention must also be given to the direction whence the light comes to each pupil. The darkest point in the room must be light enough, and for this it is necessary that each desk shall receive a sufficiency of light direct from the sky. Every one who has practiced photography knows that the sky acts more strongly than any terrestrial body upon the sensitive surface. The least favored place in the room should be within the reach of this light. Nevertheless, the direct rays of the sun should be avoided, for they will dazzle. Where such an arrangement is otherwise practicable, the advantage of a diffused light may be gained by opening windows on the north side. Then, if the seats are placed perpendicularly to the wall occupied by the windows, so that the pupils may receive the light from the left side and from above, the result will be satisfactory provided the width of the room does not much exceed the height of the tops of the windows above the floor; for, under this condition, the least favored seat will still look upon about one twentieth of the surface of the sky. With ceilings of the ordinary height, unilateral lighting answers very well for rooms that do not exceed twelve or thirteen feet in width. For larger rooms, windows may also be opened on the other side, or behind the pupils, but never in front of them.

If we open windows in opposite sides of the room, we must arrange it so that they shall not be on the south side, for that would let in the glare of noon. For this reason it would be preferable to direct the axis of the room north and south, in which case it may be expedient to temper the forenoon and afternoon sunshine with transparent curtains. This arrangement will also give us the advantage of a better lighting in the morning and afternoon during the short days of winter. A certain latitude in orientation is admissible, which may extend to