CLIMATE AND HEALTH 85 



different health conditions converge somewhat toward the left. 

 In eight cases out of twelve some of them are actually closed on 

 the left at the level of the optimum temperature. This is 

 important. It means that at the most favorable temperatures 

 a fairly high degree of moisture, that is, a relative humidity of 

 about 80 per cent for day and night together, is the most favor- 

 able. Moreover, dry weather increases the deathrate, as appears 

 from the way in which the shading becomes lighter on the left 

 side of many of the diagrams. Even at high temperatures very 

 dry air is bad, as may be seen in Figures 10, 13, 18, and others. 

 Damp, warm air is also harmful, as everyone knows, and as 

 appears in Figures 11 and 12. It is surprising, however, to see 

 how much less harm is done by warm damp air than by warm 

 dry air. I confess that this does not seem reasonable; it seems 

 to go counter to our ordinary experience. Yet it is scarcely 

 possible to question the reliability of our diagrams for they are 

 based on the official records of nearly 9,000,000 deaths and on 

 the official figures of the weather bureaus of some of the greatest 

 countries. 



When we examine the lower parts of Figures 8 to 19, the bad 

 effect of dry air becomes even more surprising. Notice how the 

 lower isopracts curve downward on the right in almost every 

 diagram. Take Figure 9 for example. At a mean temperature 

 of 30° and a relative humidity of 70 per cent the deaths are 

 85 per cent more than the normal. At the same temperature, but 

 with a humidity of 90 per cent, the deaths are only 15 per cent 

 above the normal, a gain of 20 per cent. Notice the same feature 

 in other diagrams. Figures 10, 14, 16, 18, and 19. In cold 

 weather dry air seems to be exceedingly harmful. Only in 

 southern Italy, as appears in Figure 11, does there seem to be 

 little difference in the effect of moist and dry air in winter. 

 Southern Japan likewise seems to show the same condition, for 

 there dry winter weather does no more harm than moist. As I 

 have shown elsewhere, the apparent effect of dryness cannot be 



