158 THE HUMAN FACTOB 



of Gujarat, as compared with the Koli cultivators of 

 the same locality. 



The effect of climate on the energy of workers must 

 be recognised in some degree by all, but has been 

 worked out in much detail for the varied climates of 

 the United States of America by Professor Hunting- 

 don.* From an interesting series of records of work 

 done under varying climatic conditions he has deduced 

 that the important climatic factors, so far as they 

 affect human energy, are the mean temperature from 

 month to month, the amount of change from one day 

 to another and the relative humidity. The optimum 

 temperature for factory work is a daily mean of 60° 

 for people of North European stock and 65° for people 

 of South European stock. In the case of mental 

 work a daily mean of about 40° is the best. The best 

 climate for physical and mental work combined is 

 one in which the daily mean never falls below 38° or 

 rises above 65°. Marked seasonal changes are bene- 

 ficial provided that they are not too violent. As regards 

 humidity, with an average temperature of 50° the best 

 work is done with a relative humidity of 75 per cent., 

 and with an average temperature of 65° to 70° a relative 

 humidity of about 60 per cent, is the best, while at 

 higher temperatures a lower humidity percentage is 

 desirable. The amount of change in the weather and 

 temperature from one day to another has a great 

 influence on human energy. Such changes depend 



*" Climate and Civilisation," by Ellsworth Huntingdon (Yale 

 University Press). 



