136 GENERAL SCIENCE 



lated assembly halls and schoolrooms may give to persons in 

 them a feeling of discomfort and illness due to the same cause. 



On the other hand too small an amount of moisture in the 

 air dries the air passages and skin, causing an irritation that 

 disturbs the nervous equilibrium. In our furnace-heated 

 houses in winter time it is possible by evaporation of water 

 at the furnace to control the amount of moisture in the air. 

 The humidity should range from 40 to 50 per cent of satura- 

 tion 1 . Too great humidity is enervating, and no sustained 

 physical or mental effort is possible. If the air is too dry 

 furniture shrinks, and the mucous linings of the air passages 

 are irritated and rendered more susceptible to infection. 



Usually the high following a period of clouds and rainfall 

 'brings air that is clear, cool, and bracing. One is invigorated 

 and stimulated by it. But for unknown reasons the round of 

 weather change in the United States incident to the passage 

 of highs and lows across the country is sometimes inter- 

 rupted. A high may remain stationary over any section 

 for upwards of a week, especially in summertime, bringing 

 to that section an unbroken period of clear skies, drying air, 

 and pitiless sunshine. From this nerve-racking condition 

 the advent of moisture in the atmosphere brings relief and 

 refreshment. Changes in diet and in mode of life are even 

 more important than changes in clothing to withstand the 

 "hot spells" in summer without prostration and suffering. 



"The sick man from his chamber looks 

 At the twisted brooks; 

 He can feel the cool 

 Breath of each little pool; 

 His fevered brain 

 Grows calm again, 

 And he breathes a blessing on the rain." 



Longfellow's Rain in Summer. 



1 A humidity of 60 to 70 per cent, as commonly stated in text- books, 

 would be likely in cold weather to result in condensation of vapor on win- 

 dow panes, and on walls of rooms. 



