Lastly, the war revolutionized weather telegraphy in Europe. Before the war the European forecasters were hampered by exasperating delays in the collection of reports over the telegraph lines, especially in the international exchange of observations. Wireless telegraphy had been extensively used for gathering reports from vessels and supplying vessels with forecasts, but not for the interchange of meteorological information on land. The war changed all this. Radiotelegraphic weather messages became the rule, and the advantages of the new system were so obvious that the tendency has been to retain it as far as possible since the war.
CHAPTER XX
MEDICAL AND PHYSIOLOGICAL METEOROLOGY
The starting point in any study of the physiological effects of weather and climate upon humanity is the remarkable fact that, on the hottest days of summer and the coldest of winter, in tropical deserts and amid polar snows, the temperature within the body of a healthy man remains constant to a fraction of a degree. There are slight temperature differences between different parts of the body; there is a periodic daily variation of about half a degree; and there are other slight changes, due to eating and exercise; but an internal temperature of about 98.6 degrees F. is maintained with little or no regard to fluctuations in the temperature of the air.
The body has often been compared to a building in which the temperature is regulated by a thermostat, but the comparison is not exact. The thermostat controls the temperature merely by regulating the combustion of fuel; and with the advent of mild weather we let the fires go out altogether. In the body the fires are always burning, the briskness with which they burn—or, to drop the metaphor, the rate at which bodily heat is generated—depending, above all, upon muscular activity, but also upon other causes. It is true that we possess a nervous mechanism, analogous to the thermostat, which tends to adjust the production of animal heat in such a manner as to offset the cooling effect of our environment; but this mechanism appears to be less important in maintaining our constant temperature than another, which regulates the loss of heat from the body. According to M. J. Rosenau:
“Heat is lost from the body chiefly in two ways; (1) by heat transfer, or loss by radiation, conduction, and convection; (2) by evaporation, chiefly by the evaporation of the water of perspiration. Pettenkofer and Voit estimated the loss of water by the lungs at 286 grams, and from the skin at from 500 to 1,700 grams daily. This will give some idea of the effects here concerned. The loss by heat transfer diminishes as the temperature of the surrounding air rises. The temperature of the body would rise when the atmospheric temperature goes above 70 degrees F. were not perspiration then secreted. So long as the perspiration can evaporate freely the heat production and heat loss are balanced. With a high humidity evaporation is lessened and the balance is maintained by rushing blood to the skin, which causes an elevation of the temperature of the surface, and thus the loss of heat by radiation, conduction, and convection is facilitated.”
Human sensations of temperature are paradoxical. We talk of being “hot” and “cold,” as if we belonged to the class of cold-blooded animals—the fishes and the reptiles—that actually undergo great variations of temperature, with variations in the temperature of their environment. We hear people say, for example, that they are most comfortable at a temperature of 65; yet we know that their temperature is always 98½, except just at the surface of the body.
The human body is, in fact, a poor thermometer. Our sensations do not register the temperature of the air, but they do, in a way, register the cooling power of the air, which depends upon temperature, humidity, and air movement, and they register, especially, changes in this cooling power, for within certain limits the body soon adapts itself to a constant rate of cooling, so as to lose any impression of heat or cold. When a steady outflow of heat from the body has been set up and the external cooling power is suddenly increased, we become conscious of a difference between the temperature at the surface of the body and the “blood temperature” beneath. The action of the nerves at the surface and the nerves underneath, under these circumstances, has been compared to that of a thermo-junction, in which an electric current is produced by differences of temperature. The rate of evaporation from the skin, also, has a marked effect upon our sensations of comfort and discomfort.
The common thermometer was long ago discredited as a means of measuring atmospheric comfort. Then, for a time, the wet-bulb thermometer had its day, and its indications were once published on a large scale in this country as representing the “sensible temperature,” or temperature that we actually feel. The wet-bulb thermometer is cooled by evaporation below the air temperature, except when the air is saturated with moisture, and may therefore give a rough indication of the temperature acquired by the skin when moistened with perspiration. The temperature of the skin is not, however, an accurate indication of our feelings of heat or cold, nor is it a satisfactory guide to the physiological effects of atmospheric conditions.