38 OTHER FACTS ABOUT HEAT 



saturated and condensation begins is called the dew 

 point. 



28. How Chills are Caused. The discomfort we feel in an 

 overcrowded room is partly due to an excess of moisture in 

 the air, resulting from the breathing and perspiration of 

 many persons. The air soon becomes saturated with vapor 

 and cannot take away the perspiration from our bodies, and 

 our clothing becomes moist and our skin tender. When we 

 leave the crowded "tea" or lecture and pass into the colder, 

 drier, outside air, clothes and skin give up their load of mois- 

 ture through sudden evaporation. But evaporation requires 

 heat, and this heat is taken from our bodies, and a chill results. 



Proper ventilation would eliminate much of the physical 

 danger of social events ; fresh, dry air should be constantly 

 admitted to crowded rooms in order to replace the air satu- 

 rated by the breath and perspiration of the occupants. 



29. Weather Forecasts. When the air is near the satura- 

 tion point, the weather is oppressive and is said to be very 

 humid. For comfort and health, the air should be about 

 two thirds saturated. The presence of some water vapor in 

 the air is absolutely necessary to animal and plant life. In 

 desert regions where vapor is scarce the air is so dry that 

 throat trouble accompanied by disagreeable tickling is preva- 

 lent; fallen leaves become so dry that they crumble to dust; 

 plants lose their freshness and beauty. 



The likelihood of rain or frost is often determined by tem- 

 perature and humidity. If the air is near saturation and the 

 temperature is falling, it is safe to predict bad weather, be- 

 cause the fall of temperature will probably cause rapid con- 

 densation, and hence rain. If, however, the air is not near 

 the saturation point, a fall in temperature will not necessarily 

 produce bad weather. 



The measurement of humidity is of far wider importance 



