Very often this system is used in connection with the ventilation. The radiators are placed in the basement or in another convenient place and cool fresh air from the outside is passed over them and warmed. It is then forced into the rooms. Very often this air is washed, as described in the chapter on ventilation, and thus freed from suspended matter. At the same time the relative humidity can be controlled and this is very essential, not only as a means of providing air that is most desirable for breathing, but also in point of fuel economy, since air of high humidity is more easily heated and is more desirable in conserving the heat of the body as has already been explained. Steam heating is especially suitable for high and irregularly shaped buildings. The fact that the radiators and pipes are empty when not in use reduces the risk of damage to the house furnishings from bursted or leaky pipes. It is well to have the radiators placed near windows so that in ventilating the air will pass over them and be warmed before entering the room. CHAPTER VI LIGHTING LIGHTING ADAPTABILITY OF EYE TO LIGHT DIFFERENCE IN INTENSITY OF LIGHT TIME REQUIRED FOR ADAPTATION THE EYE MECHANISM OF EYE ACTION OF LIGHT UPON THE EYE INTELLECTUAL ADAPTATION NECESSARY VALUE OF SUNLIGHT EFFECT UPON HEALTH ACTION IN NATURE NATURAL LIGHT IN BUILDINGS DIRECT RAYS OF THE SUN FACTORS DETERMINING THE AMOUNT OF LIGHT ADMITTED REFLECTED LIGHT LOSS OF LIGHT THROUGH DIFFERENT GLASS WINDOW AREA REQUIRED ARTIFICIAL LIGHTING EFFECT UPON THE EYES EVOLUTION OF LIGHTING SYSTEMS BEST MEANS OF LIGHTING OBJECTIONS TO OPEN BLAZE FOR LIGHT DIRECTION OF LIGHT PSYCHOLOGICAL EFFECT OF LIGHT INFLUENCE UPON THE EMOTIONS SOFT LIGHT SOOTHING BRIGHT LIGHT STIMULATING SYSTEMS OF LIGHTING DIRECT INDIRECT SEMI-INDIRECT EFFECT OF INSUFFICIENT LIGHT CHAPTER VI LIGHTING Adaptability of Eye to Light The eye has a great range of adaptability to the intensity of light. This is evidenced by the fact that the eye is readily adapted to the intensity of the bright sunlight or to the soft rays of the moon. In both instances there is no disturbance in vision, even though the intensity of illumination at midday when the light is brightest is almost a million times greater than the illumination from the full moon on a clear night. This adaptation takes place so perfectly and so independent of the educated mind that we give little thought to the great difference in intensity of light.