IMPORTANCE OF VARIABILITY 101 



This little table shows that at the beginning of the experiment 

 the average temperature of the two rooms was the same. As the 

 experiment progressed the temperature of the two rooms became 

 more different, until in the last period the dry room was 2.1' 

 warmer than the wet. Thus, judging by the results obtained from 

 a study of deaths and of factory operatives, the dry room had two 

 disadvantages : it was too dry, and its temperature was too high. 

 The variability of its temperature, however, grew steadily more 

 favorable. From having a variability 18 per cent less than that 

 of the wet room at the beginning of the experiment it changed to 

 a variability 15 per cent greater in the second period, 29 per cent 

 in the third, and 54 per cent in the final. Thus the greater varia- 

 bility seems to have overcome the handicap both of dryness and 

 of too high a temperature. Hence we conclude that this experi- 

 ment is inconclusive so far as humidity is concerned, but furnishes 

 weighty evidence as to the value of a variable temperature. 



It is to be hoped that further experiments as to the air of school 

 rooms may be carried on. If this is done strict attention should 

 be paid to variability, and the humidity in the wet room should 

 be much greater and the temperature lower than in the experiment 

 described above. In that case I feel confident that humidity will 

 be found to have a real effect on mental activity. 



The importance both of the mean temperature and of the 

 variability is shown by another experiment carried on by the 

 Ventilation Commission in cooperation with the Bureau of Child 

 Hygiene of the Department of Health of New York City. During 

 the period from February 19 to April 8, 1916, records of respira- 

 tory diseases were kept in eight New York schools having fifty- 

 eight classrooms and 2,541 children, while from November 4, 1916, 

 to January 27, 1917, similar records were kept in twelve schools 

 having seventy-six rooms and 2,992 children. A corps of trained 

 nurses under the supervision of physicians examined the children 

 daily and looked up those who were absent. The rooms were 

 divided into three groups: (I) cool rooms where the windows were 



