rooms, particularly in the homes of the poor in the winter time. Add to these difficulties the further fact that by habit and association we have learned to base our visual estimation and discrimination of things on their appearance in broad daylight, and we begin to appreciate the baneful optical effects of the frequent obscuration of the sun by smoke clouds, by smoke-produced water clouds and fogs, and by the filling of the atmosphere with opaque particles. As stated before, particles in the air and fogs may reduce the limit of visibility from one mile to less than one city block. During the dark days which are common in manufacturing cities the lights must be kept burning in the homes, schools, shops and factories--anywhere, in fact, where close eye work must be done--all day. Almost always the lights must be turned on very early in the evenings. Very frequently the intensity of artificial illumination does not meet the requirements of visual health. Aside from this, artificial illumination entails a considerable economic loss. Worse still is the condition of those who, through financial limitations, must work in the dark gloom of smoky days without the aid of artificial light. The writer has shown in a special experiment on the visual estimation of distances that bright objects are judged to be nearer the observer than similar black objects when placed at the same distance (25). This being the case, it is evident, as indeed common observation indicates, that anything on which the eyes must be fixated in darkened illumination will be imperfectly envisaged. To overcome this optical handicap, there is a strong tendency to move the object too near the eyes. If done repeatedly this entails a severe strain on the muscles of accommodation, causing increased muscular fatigue, which may result in muscular paralysis, imbalance or dioptric distortions. On the other hand, by illuminating an object with good daylight it will be made to appear nearer to the eye. The result is that objects will actually be held at a further distance and distant objects will be seen without eyestrain. If an investigation could be carried out on a large scale with sufficient accuracy, it is possible that a greater prevalence of myopia, myopic astigmatism and other eye disorders would be found in densely smoky cities than in smoke-free cities, so that a positive correlation would be found to exist between eyestrain or certain eye disorders and atmospheric smoke.