Weather is not the same as climate. Climate is the average condition of the weather, such as average temperatures, amounts of rain or snow, averages of sunshine, wind, and humidity, and the number of days when certain weather conditions may be expected in a month or year.

Everybody is affected in mind and body by climate and changes in the weather. A long period of the same kind of weather may be depressing or irritating. The constant heat of the tropics is depressing, but an occasional hot day is not. Unless changes of weather are too severe, they are stimulating to mind and body. Human comfort depends largely on temperature, but also on air movement and moisture in the air. In general, more air movement makes the temperature seem lower.

An in-between climate with frequent but mild changes in the weather is usually considered the best kind. Most of the vigorous and progressive peoples are found in fairly cold climates with large seasonal changes of weather. It is well known that the climate is important in the treatment of disease. The choice of climate depends on the kind of disease and the physical condition of the patient. Climate is also the direct source of certain ills such as sunstroke, snow blindness, and frostbite. Many diseases occur mostly at certain seasons, such as infantile paralysis in late summer and the common cold in the winter.