3l8 HUMAN BIOLOGY 



In this connection the question at once arises whether 

 the good effect of falHng temperature is completely counter- 

 acted by the bad effect of rising temperature. Among 

 plants, as we have seen, this is not the case; the net effect 

 of the two types of change is stimulating. Among men the 

 most extensive of the few investigations along this hne 

 is that of the Committee on the Atmosphere and Man in 

 New York City. There during a six-year period, a very 

 systematic relationship was found between the average 

 change of temperature from one day to the next during 

 ten-day periods and the deaths at the end of such periods. 

 If the variability is small, no matter whether the temperature 

 be high or low, the death rate is high. When the average 

 variability amounts to 3° during most of the year, or to 4° 

 or 5° during the winter, the death rate is at a minimum. 

 If the variabihty rises higher, the death rate likewise rises, 

 but even with the most extreme variabihty it is not so 

 high as with extreme uniformity. In New York variabihty 

 appears to have more effect on health than does humidity 

 and about half as much as mean temperature. If such a 

 relationship is universal, as appears to be indicated by many 

 scattered bits of evidence, variabihty must be of the utmost 

 importance in determining man's health and energy all 

 over the world. 



Other things being equal, extreme uniformity of tem- 

 perature from day to day is decidedly undesirable; extreme 

 variabihty is also undesirable, but to a less degree; and 

 between the two extremes hes the optimum. From this 

 point of view the chmate of Newport in Rhode Island appears 

 to approach the ideal quite closely, while chmates with 

 great uniformity as in southern Cahfornia or very violent 

 changes as in central Siberia are far from the optimum. 

 Apparently the moderately variable type of chmate is 

 good by reason of its changes not only in temperature, but 

 in humidity, sunshine, and wind. 



This is as far as we can carry our study of climatic optima. 

 We may hazard the guess that the optimum atmospheric 

 pressure is found within one or two thousand feet of sea level, 

 and that the optimum conditions of sunhght are found in 

 different latitudes according to the pigmentation of the skin. 



