Whether the retinal excitation by the sun’s rays exerts any stimulating influence is not known. It is known, however, that red colors are stimulating. They excite some animals (for example, cattle, frogs and turkeys) and increase muscular strength. Thus Fere obtained the following strength records: with ordinary light, 23 units; with blue, 24; with green, 28; with yellow, 30; and with red, 42 ([29]). Colors, as is well known, possess marked affective qualities, due not merely to the affective tone of the sensation and the sense feeling, but to the affective elements of consciousness, namely associations, emotions and sentiments ([29]). That sunlight does exert psychic influences apart from any specific retinal influence is a matter of common experience. Nevertheless, the most important visual influence of sunshine is perhaps not the emotional satisfaction, cheer or exuberance which it engenders, but the optical value of good daylight. Daylight is relatively colorless because it contains both chromatic and achromatic light. A bright colorless illumination is best from the standpoint of visual efficiency, health and affective quality. It is less fatiguing than a colored light or than intense or dull artificial light. Electric lights are often too intense because of the proximity of the light or because the rays are thrown directly into the eyes or directly upon the object under observation. They thus over-stimulate the sensitive layers of the retina, and this may cause degenerative changes. Mercury vapor lamps and old Welsbach burners emit a greenish flame whose affective quality is very disagreeable to many persons. Many of the gas jets in common use, unless equipped with incandescent burners, not only give a weak flickering, dirty yellowish light, which is extremely fatiguing and irritating to the eyes, but they also vitiate the air of the living 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.
Dark days repress the infra-red rays and thus diminish solar energy. In fact, on excessively smoky days only a small amount of solar heat penetrates to the earth’s surface. This circumstance may be rather welcome to man during the excessive heat of the summer (although objectionable to plant life), but during the winter time it may cause much misery, particularly among the poor, because of the excessive diurnal cold during this season (smoke clouds elevate the nocturnal temperature). It is also possible that the reduction of the heat profoundly affects the habits of the community. Thus Dexter ([5]) has shown that low temperatures (10°) produce an excess of drunkenness amounting to 38%, while high temperatures (85°) decrease drunkenness to the extent of 40%. High winds, which lower the bodily temperature, also increase dissipation. The increased tendency to dissipate probably results from an attempt to seek forgetfulness from misery in alcoholic narcosis, or from an attempt to artificially elevate the body temperature by indulgence in drink.
Dark days exert a particularly sinister influence upon working people. One factory head has ventured the opinion that a disagreeable day yields about 10% less in labor returns than an agreeable day. During human labor the chemical products of activity are greatly augmented. The amount of carbon dioxide given off during a day of work is nearly twice as much as during a day of rest. Observations on the embryos of frogs also indicate that more carbonic acid is given off when it is light than when it is dark (Moleschott). Therefore, merely reasoning from these premises, it would appear that the bodily waste products from muscular activity, and probably also to a lesser extent from mental activity, are more injurious on dark than on bright days. Not only so: dark, sunless days are likely to be moist, rainy or foggy. During foggy days particularly the poisonous gases are unable to rise because of the atmospheric stagnation that obtains during fogs. On these days the amount of carbon dioxide may sometimes be increased from 200 to 300% as compared with clear days. Dexter ([5]) attributes the devitalizing, depleting effects of fogs to lowered electrical potential. He regards atmospheric states of high electrical potential as stimulating and vitalizing to animal life. But it has not been conclusively shown that the electrical potential is decreased during fogs. On the contrary, it is maintained that fogs, especially thick, winter fogs, usually raise the potential ([14]), while the low ground fogs in late summer and fall have been found to lower the potential. But then, again, Chauvenau found that thick, city fogs exercised no influence on the electrical potential. It has, therefore, not been proved that lowered electrical potential has anything to do with the depleting effects of fogs; but I am of opinion that the suppression of the tonic chemical rays of the sunshine is an important factor.
Again, moisture in the atmosphere may become very injurious because it absorbs the poisonous exhalations of living organisms. Hence the air which must be breathed on moist, dark days is liable to be surcharged with toxic waste products which poison the individual.
The effects of moisture per se vary with the temperature. During warm, moist atmospheric conditions there is diminished evaporation from the lungs, fewer red corpuscles (because there is less oxygen in the air), increased tendency towards intestinal troubles, lowered resistance, and greater mental and bodily fatigue and prostration; while during cool moist weather catarrhal, respiratory and rheumatic affections are aggravated ([3], [26]).
It has been observed that changes in the density of moisture affect the sensitivity for odors, tastes and touch. Tea-tasters do their best work on fair days ([11]).
That the electrical potential decreases with increase of humidity has, apparently, been established, except under conditions of fog. It we grant that a state of high electrical potential stimulates and energizes the organism, then a part of the devitalizing effect of humid days must be ascribed to a lessened potential.
Not the least detrimental effect of the dark smoke strata of our cities is the fact that they intercept the bactericidal rays of the sun, namely, the blue and ultra-violet rays. These rays either check the growth of, or completely exterminate, various kinds of pathogenic bacteria ([1], [6]). Their deadly effect on the tubercle bacilli is universally recognized. Indeed, as Sternberg points out, sunlight is one of the most potent and one of the cheapest agents for the destruction of pathogenic bacteria. Less diseases are found during sunshiny than foggy or cloudy weather, while the death rate increases considerably during fogs. Thus during a November fog in Glasgow the death rate rose to 13.9 while in other Scotch towns free from fog it was only 3.3. But the increase in the mortality is not merely due to the fact that the sunless, foggy states lower the temperature and favor the growth of micro-organisms, but the water globules absorb particles of dust and acrid smoke and the toxic products of respiratory waste. (In factories dust particles become vehicles for the products of human fatigue.) The inhalation of these products irritates and poisons the mucous membrane. Moisture is particularly injurious in cases of pathological nasal obstruction. We should not forget, then, that fog and particularly dense smoke fog may entirely extinguish those rays of the sun which exert not only a germicidal action, but which also possess a tonic, vitalizing quality, viz., the short wave lengths.
Now, since smoke diminishes the sunlight, reduces or suppresses the heat giving infra-red and the tonic ultra-violet rays, and diminishes the electrical potential (at least during certain states of the atmosphere); since smoke increases humidity, both during cold and warm weather, but particularly during cold states; and since it also increases fogs, and since fogs and humidity tend to increase the poisonous, bactericidal and solid contents of the air and to decrease the electrical potential and the heat light rays; it is evident that smoke must exert an important influence on human health, happiness and efficiency, and that the smoke nuisance must be regarded as a problem of very vital concern to any community that would conserve the vital efficiency of its citizenship.
The assumption that smoke is an immediate, indirect conditioning factor in human behavior, because of its sinister influence on weather states (aside from its intrinsically pernicious qualities), is at least suggested by the only comprehensive study extant of the relation of weather to abnormal behavior: viz., Dexter’s investigation of the influences of various weather states on the conduct of a large number of child and adult offenders in Denver and New York City ([5]). The data which he studied included records of misdemeanors in schools, penitentiaries, and hospitals for the insane, arrests for assault and battery, for suicide and murder, records of deaths and bank errors, and strength tests. From this study Dexter arrives at the conclusion that days with high temperature and high humidity are unfavorable to metabolism. More specifically: anabolism is favored by high temperatures (though high temperatures deplete the vital reserve), high winds (because of better ventilation), and fair days with low humidity; while katabolism is increased by low temperatures, high humidities, high barometric pressures, rainy and cloudy days, and calms. (During fogs there is usually a condition of calm and a fall of temperature.) The katabolic weather states tend to deplete vitality, lower the vital reserve and augment the death rate, while the anabolic states tend to stimulate, invigorate, irritate and increase the nervous tension. Conformably with this classification of weather states Dexter finds statistically that anabolic conditions increase all the data which are of the nature of offenses.