IMPORTANCE OF VARIABILITY 99 



be too great. The Pacific Coast of the United States, especially 

 in the northern portions, has an admirable range of temperature, 

 but not enough variety. Further discussion of this point is un- 

 necessary. The reader can apply the principles for himself. 



Since mankind is obliged to live in all sorts of climates, one of 

 the greatest problems of civilization is to provide an artificial 

 climate that shall be as nearly ideal as possible. I cannot illus- 1 

 trate this point better than by discussing two experiments which 

 form part of one of the largest and most careful attempts that 

 has yet been made to discover just what kind of artificial climate 

 is most favorable. The experiments were carried on by the New 

 York State Ventilation Commission under the chairmanship of 

 Professor C. E. A. Winslow. They were planned by a group of 

 the most competent experts to be found in the American metropo- 

 lis. They were conducted with the utmost accuracy, and without 

 any prepossessions as to what results ought to be found. 



In one of the experiments a class of forty-three school children 

 was divided into two groups of approximately the same size. The 

 greatest pains were taken to see that the average mental ability of 

 the groups was equal. Then from December to March one group 

 was kept in a school room where the conditions of ventilation and 

 temperature were as perfect as possible, but where the air had 

 the ordinary dryness characteristic of our winters. The relative 

 humidity averaged 28.7 per cent. The other group was kept in 

 a similar room except that the air was humidified and the relative 

 humidity averaged 42.2 per cent. In both rooms the temperature 

 averaged about 67°. Two teachers divided the care of the two 

 groups, each teaching certain subjects to both groups. At the 

 end of each month the rooms were interchanged; the pupils who 

 had been in the dry room went to what had been the damp room, 

 which now became the dry room. Thus while the conditions of 

 the air remained unchanged for each group, the rooms were inter- 

 changed so that there was no chance for one set of pupils to have 

 an advantage because of being in a room with a better outlook. 



