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.