100 WORLD-POWER AND EVOLUTION 



The two groups were tested at the beginning and end of the 

 experimental period by examinations, lasting in all seven hours, 

 but covering several days. The children's progress was measured 

 by the difference between the score made by each pupil in a given 

 test the first and second times. Measured by this standard the 

 children in the drier room, contrary to what would be expected, 

 made a very slightly better showing than the others, although 

 their superiority was not enough to be significant. Thus there 

 seemed good ground for the conclusion that a difference of about 

 13 per cent in relative humidity does not make any appreciable 

 difference in the mental activity of school children. The obvious 

 inference is that it will not pay to attempt to improve the health 

 of the community by dampening the air in our dry winter houses. 



This conclusion is at variance with the lesson taught by our 

 study of millions of deaths. In trying to find some explanation 

 of this anomaly it occurred to me that there may have been a real 

 but unnoticed difference in the two rooms because dry air loses 

 its heat faster than moist air. Hence the dry room may have 

 been more variable than the other. Through the courtesy of the 

 chairman of the Ventilation Commission I was able to test this by 

 means of the original thermograph sheets from the two rooms. 

 Dividing the sixty available sheets into four consecutive sections 

 of fifteen days each, I found that the actual temperature and the 

 variability were as follows: 



