298 THE SEASONS CLIMATE AND HEALTH 



low vitality and low resistance to the attack of the influenza 

 germ, or other similar germs, which produce the effects we 

 commonly hear spoken of as "catching cold" (see Arts. 512 

 and 513). 



When we come to realize that the relative humidity changes 

 greatly from day to day, sometimes changing 10, 20, or even 

 50 per cent, within a few hours, we see how unscientific and 

 unwarranted the assumption is that we are likely to "catch 

 cold" in the evening on account of the low temperature and 

 dampness of the air. The importance of studying humidity 

 and of knowing how to secure the proper indoor relative 

 humidity will become more evident when we study ventilation, 

 Chap. VI. 



The student should keep a daily record of relative humidity 

 out of doors for one month, noting the changes in weather 

 during that period. 



C. WINDS 



318. Wind, Another Important Element of Climate. The 



temperature and humidity may be the same for two different 

 localities. But if one be a sheltered place where wind veloci- 

 ties are low while the other be exposed to high wind velocities, 

 we know from experience that the exposed place seems to be 

 much the colder and more uncomfortable in winter and much 

 the cooler and more comfortable in summer (Art. 231). Pro- 

 tection against the chilling effect of the wind in winter is nec- 

 essary. The clothing we wear, the wool, the fur and the hair of 

 animals, and the feathers of birds, all serve as a protection 

 against the chilling wind by retaining a layer or envelope of 

 warm air next to the body. High winds disturb this layer of* 

 warm air, thus cooling the body. 



319. Wind Velocities in the United States. The Weather 

 Bureau records for years past give fairly satisfactory in- 

 formation regarding the wind velocities. The principal facts 

 of wind velocity over the United States are easily shown (Fig. 

 224). From this map we see that the highest average wind 



