Human comfort, so far as it is determined or modified by atmospheric or climatic environment, depends on a greater number of factors than is generally supposed. Our customs and activities are frequently altered to meet the respective conditions that arise. Muscular work, clothing, movement, artificial heating or cooling and ventilation may be concerned with the physiologic well being of man so far as this is modified by his atmospheric surroundings. Nearly a century has elapsed since Heberden pointed out that the ordinary mercury thermometer is a very inadequate instrument for measuring the physiologic effects of atmospheric conditions. It merely accounts for that part of the body heat lost by radiation and convection, whereas a great part of the body heat resulting from metabolic processes is eliminated by evaporation from the surface of the body. The ability to lose heat in the latter way depends in part on the relative humidity of the atmosphere. Although there are ways of measuring this and translating the results into terms of experience, the senses have usually been the best guide. Movement of the air is a further factor that favors removal of heat -- perhaps the greatest factor of all, because the cooling resulting from evaporation and convection largely depends on the velocity of the air. Clothing may interfere with or modify the effects. As these different modifying features -- temperature, relative humidity and air motion -- may be independently variable, it is difficult to establish a single standard of comfort. Heat prostration may occur at quite unlike external temperatures in different places. The art of securing human comfort in the face of unfavorable environment is being studied more carefully than it has been in the past, particularly because of the demands of certain industries and the newer problem of the invasion of the tropics by persons from more temperate regions. Some indexes of the conditions to be established are therefore quite desirable. The latest investigations of the Bureau of Mines show that while a temperature of 57.7 F. with no air motion is too cold for comfort, a temperature of 85.6 F. with an air motion of 500 feet a minute is too warm to be comfortable. Perhaps two intermediate conditions -- say 70.8 F. at 50 feet a minute and 75.8 F. at 100 feet a minute -- will appeal to the comfort of the average person, provided the humidity is not outside the limits of the ordinary range. It is the problem of many arts to contribute toward securing these optimal environmental conditions for man. Here the stoker, the refrigeration expert, the clothier and furrier vie with one another in their attempts to thwart the machinations of the ubiquitous "weather man."...