156 SEASONAL CHANGES AND HISTORIES. 



course favorable to the multiplication of broods 

 in butterflies whose history allows a repetition of 

 the same cycle more than once a year ; the length 

 of the winter is of slight consequence, as long as 

 the insects can survive it ; and it can have no in- 

 fluence upon the number of broods, unless there 

 be species (of which we know nothing) able to re- 

 sist a cold winter only in certain stages of exist- 

 ence, and a multiplication of whose broods might 

 require some pliability in this respect. Not 

 only, too, are our summers longer and hotter, but 

 they enjoy a marked preponderance of sunshine, 

 as compared with European summers ; and this 

 alone would almost seem capable of producing 

 the variation we have noticed in the number of 

 broods. 



Differences will be found in all other climatic 

 phenomena of the two continents. " From 

 Europe as a standard," says Blodgett,* " the 

 American climate is singularly extreme both in 

 temperature, humidity, quantity of rain, wind, 

 and cloudiness or sensible humidity. The oscilla- 

 tions of the conditions are greater, and they 

 vibrate through long measures above and below 

 the average. All the irregular as well as regular 

 changes are of this sort, and the European observ- 

 er defines the climate as directly antagonistic to 



* Climatology of the United States, p. 221. 



