304 HUMAN BIOLOGY 



tures. The chief difference is that the most rapid work is 

 done when the outside temperature averages 60° for day 

 and night together instead of 66° to 70°. One reason for this 

 lower optimum is doubtless that when people are at work 

 they warm themselves at least a httle and therefore prefer a 

 temperature somewhat lower than that which is most 

 favorable for people who are inactive, and for those who are 

 ill. Perhaps, too, the lower optimum means that in the 

 work of factory operatives not only physical energy but 

 mental activity is required so that this curve tends some- 

 what to approach the mental curve which lies just above. 

 The optimum for football is obviously much lower than for 

 factory work. 



The curve for "Mental Energy" represents the scholar- 

 ship records of about sixteen hundred students at West 

 Point and Annapolis. It resembles the curves for health 

 and physical energy except that the optimum lies at about 

 38° and there is a plateau from that point to the physical 

 optimum at 6§°. Although the reliability of this curve is 

 not so great as that of the others, several investigations 

 confirm the general thesis that the optimum temperature 

 for mental activity under our conditions of clothing, housing, 

 and diet is lower than that for physical activity. 



Taken as a whole. Figure i illustrates the laws of both 

 climatic limits and climatic optima so far as temperature is 

 concerned. It suggests that for every living creature there 

 is a distinct degree of activity for every condition of tem- 

 perature. The activity is highest at the optimum; with 

 lower temperatures it falls off rapidly at first and then more 

 slowly until the lower limit is reached. Above the optimum 

 the activity tends to decline rapidly and under all cir- 

 cumstances appears to cease at least by the time a mean 

 temperature of about 100° is reached. The exact position 

 of the optimum appears to vary from one individual or race 

 to another, but the general law is of universal application. 



The four upper curves of Figure i illustrate the further 

 law that the optimum temperature varies according to the 

 type of activity. When taken together they suggest that 

 so far as temperature is concerned the best climate for 

 people of European ancestry who live under our conditions 



