270 WORLD-POWER AND EVOLUTION 



above 65 per cent and at a temperature of about 61° when the humidity 

 fell below 20 per cent. The fact that they had just been actively exer- 

 cising accounts for the apparently low optimum. 



On the basis of these experiments and others I have prepared the 

 following table. It shows the approximate dry bulb temperature that 

 would be necessary in a house under different conditions of weather 

 in order to make people feel as warm as they would feel with a temper- 

 ature of 64° and a relative humidity of 75 per cent. 



Table of Equivalent Temperatures 



Column C shows that on very cold winter days with the thermometer 

 at 10°, the air in the house will have to be heated to 76° in order to 

 feel as warm as greenhouse air. It would then be as dry as the air of 

 the driest deserts. Such cmiditions prevail frequently in our houses. 

 That is why we shiver in cold weather even when the thermometer is 

 comparatively high in the house. That appears also to be one chief 

 reason why we catch so many colds, suffer so much from winter sick- 

 ness, and have so much poorer complexions than our English cousins. 

 The English, be it noted, live most of the time in fairly moist air; we, 

 on the contrary, parch our poor mucous membranes to such an extent 

 that they cannot resist the attacks of germs. The matter can scarcely 

 be put too strongly. Recall how disagreeable the dryness of the air 

 feels when the heat is first turned on. The heat itself may be grateful, 

 but it gives the nose and throat a disagreeable feeling. Consider, too, 

 how many people suffer from rough skins and from cracks around the 

 finger nails. The outside temperature may have something to do with 

 this, but apparently the indoor dryness is a much more potent cause. 



