PHILOSOPHICAL SOCIETY OF WASHINGTON. 167 



cessive heat periods, which occur after the middle of August, the 

 daily mortality declines. 



4. The detrimental influence of summer temperature is intensified 

 by sudden and acute elevations and falls. 



5. Children under one year of age are most numerously and 

 seriously affected. 



Heat exhibits its deleterious influence in another and very impor- 

 tant relation. It is one of the many conditions which, in conjunc- 

 tion, make up a season. A comparison of the statistics of the 

 weekly mortality from diarrhoeal diseases in the principal cities of 

 the country grouped according to latitude, will exhibit the gradual 

 increase of these diseases with the gradual advance of the summer 

 solstice northward until it reaches its maximum during the period 

 when all the elements which complete the season of summer are in 

 their fullest activity ; also a gradual decline with the return of 

 the winter season. 



The total movement of the wind is, perhaps, a moye important 

 influence than is generally believed. A comparison of the mortality 

 data with the records of the monthly measurement of the wind, 

 supplied by the Signal Service Bureau for the years 1875, 1876, 

 1877, 1878, 1879, and 1880, shows : 



1. July is the month of greatest mortality and least movement 

 of the wind. 



2. The nearer the monthly movements of the wind approach uni- 

 formity, the less the mortality for summer diarrhoeas. 



3. Equality of climate corresponds with uniformity of and mod- 

 erate or small movements of wind, and small mortalities. 



4. Wide ranges of temperature correspond with large movements 

 of wind and high mortalities from diarrhoeal diseases. 



5. Weekly mortalities from diarrhoeal disease increase correspond- 

 ingly with advance of the summer solstice northward, increasing 

 and greater range of temperature, and larger and more fluctuating 

 movements of wind. 



Relative saturation of the air bears no constant relation to mor- 

 talities. Moisture in relative excess to the heat of an impure and 

 stagnant atmosphere is the condition which supplies the most satis- 

 factory explanation of its detrimental influence. 



