These variations in health and energy have an important relation to business. During the 24 worst months of the four years shown in Fig. 18, 25 per cent more people died in both Connecticut and Pennsyl vania than during the 24 best months. In other words, if the climatic conditions of the worst 24 months, together with their indirect effects ; through food, clothing, indoor air, and diseases, could have been neutralized, the number of deaths each year would have been dimin ished by about 2000 in Connecticut and 12,000 in Pennsylvania. In the United States as a whole there are about 1,400,000 deaths each year. At the rate determined in Connecticut and Pennsylvania, there would be about 150,000 fewer deaths each year if by proper care the worst half of the months could be made as good as the best half. Every person who dies while his work is still of value represents an irre placeable loss. In the factories the difference between the better and the worse halves of the .months shown in Fig. 18 amounts to about 4 per cent, but would be far greater if people did not feel obliged to work in spite of their feelings. Yet even at this rate, if we suppose each of the gainfully employed workers in the United States to be worth two dollars a day and to work 250 days per year, the country would gain about 00,000,000 if people worked as well in the worse half of the year as in the better. The effect of the seasons on mental work appears to be much the same as upon physical work, except that peo ple's minds apparently work best at a somewhat lower temperature than their bodies. Thus, each year the variations of the weather appear to cause a loss of hundreds of millions of dollars from deaths and poor work, in addition to all the loss due to sickness, and to the interruption of the work of others which sickness and death always cause. So important is this matter that many factories employ doctors and nurses, and provide recre ation grounds and hygienic lunch rooms in order to improve the health and energy of the operatives.
Effect of Tem perature on Man's Mind and Body. Let us now see what particular conditions of cli mate cause the variations from season to season. Fig. 19 shows the effect of tempera ture alone, without respect to other conditions or to the season at which a given temperature happens to occur. The upper curve shows that in the investiga tions thus far made, when the average temperature out-of-doors for day and night together was low, the marks of a large group of students were also low, which means that their minds were inactive. When the average temperature rose aboutto freezing, the marks began to improve.
When the outdoor temperature averaged 40°, that is when it rose to perhaps 50° by day and there were light frosts at night, mentality seemed to be at its best, while at high temperatures the mind became less active. The third curve in Fig. 19 shows variations in health as deter mined from the deaths of milliods of people and from records of illness. Here, just as in the mental curve, the ability is relatively slight on cold days, but increases with rising temperature until the highest point, is reached at about 64°, that is, when the thermometer rises to about 70° or more at noon and falls to 55° or so at night. Thus there seem to be indications of a mental optimum at an average outdoor temperature of about 40° and a physical optimum at about 64°. Since man's total
ability depends upon the combination of mental and physical activity, his general capacity for work probably varies according to the second curve in Fig. 19, which is a combination of the two upper curves, mental and physical, giving equal weight to each.
The other curves suggest that man is much like other forms of life. One curve shows the amount of carbon dioxide liberated by the cray fish at different temperatures. This is a measure of the animal's activity. At temperatures a little above freezing the life processes of this cold-blooded animal practically cease. With warmer conditions its activity rises steadily to a maximum not far from and then falls off rapidly. In the much lower form of life shown by the infusoria curve the rate at which the cells divide varies in the same way as the activity of the cray-fish, except that the optimum is a little higher. The same is true of plants whose optimum in most cases is highest of all. Fig. 19 illustrates the fact that among all living beings the same great law of optimum temperature apparently prevails. Man boasts that he is superior to nature, but each advance in knowledge shows rrlre conclusively than before that he is governed by the same laws winch govern the rest of creation. The only difference is that man has the power to overcome part of his limitations.
The Effect of Atmospheric Moisture.—Among the climatic elements other than temperature, people often suppose that the barometric pressure is highly important, but except at high altitudes it is now generally agreed to be important chiefly because of its effect upon variations in temperature and humidity.
It is hard to separate the effects of humidity from those of tem perature. In general the investigations thus far made suggest that people work best with high humidity in winter, while in the spring a relative humidity of about 75 per cent and in summer about 65 per cent appears best. This seems to indicate that it is not the relative humid ity but the absolute humidity which counts. Most people work best when the air contains 4 or 5 grains of moisture per cubic foot of space. At a temperature of 80° an absolute humidity of 5 grains means a rela tive humidity of 45 per cent; at 64° about 70 per cent; and at 56° about 100 per cent. If the air is colder than 56° it cannot hold as as 5 grains per cubic foot. Apparently this is an important reason why health and efficiency fall off so badly in winter even though we protect ourselves from the oustide air by means of heated houses. Within our houses the winter air is often extraordinarily dry. This not only parches the mucous membrane and leads to colds, but makes people sensitive to drafts. In the autumn we sit in a temperature of 65° and feel comfortable. As soon as the rooms are heated, how ever, many people feel chilly if the thermometer falls below 70°. The extreme dryness causes rapid evaporation from the skin and that makes us cool even though the temperature is higher than is good for health. If people would live in cool and properly humidified but not damp rooms not only would they probably soon find themselves com fortable but their health, work, and pocketbooks would presumably he better off.