PLATE IV. 



The Advance of Autumn 

 After A. G. Hogbom 



The advent of autumn is proclaimed by the same degree of temperature 

 as that which ushered in the spring. The map shows the dates of the 

 return of isotherm 48° F., and its march southwards over the various regions 

 of Europe. 



The appearance of autumnal climatic conditions has an important bearing 

 upon the dates on which the different kinds of summer birds quit the more 

 northern portions of the Continent to proceed to winter retreats in warmer 

 climes. 



