1876.] A Cosmopolitan Butterfly. II. Its History. 605 
present attainments, which marks us as a hurrying, energetic, 
enterprising people. My own experience has been that studies of 
precisely the same nature and undertaken under similar external 
conditions are accompanied by a very different mental state on the 
two continents. In Europe we are content to plod industriously 
on, unconscious of the need of relaxation; in America we bend 
with nervous intensity to our work, and carry the same excite- 
ment into the relaxation which such a life inevitably demands. 
After a long absence in Europe, a keen observer may even be 
directly conscious of this quickened life. ` 
Now to what shall we ascribe such peculiarities in animal life ? 
Naturally we look to climatic influences, and our attention is first 
attracted by the well-known fact that, if we compare two places 
in Europe and America having the same mean annual tempera- 
ture, the extremes of variation will prove much greater on this 
side of the Atlantic. For example, while the mean annual tem- 
perature of New York is about the same as that of Frankfort, 
the summer temperature of the former is that of Rome, and its 
winter that of St. Petersburgh. Moreover, the changes from 
summer to winter and from winter to summer are more immedi- 
ate in America, or, in other words, the summers and winters are 
longer (by about three weeks). Such long and hot summers are 
of course favorable to the multiplication of broods in butterflies 
Whose history allows a repetition of the same eycle more than 
once a year ; the length of the winter is of slight consequence, as 
ong as the insects can survive it; and it can have no influence 
upon the number of broods, unless there be species (of which we 
know nothing) able to resist a cold winter only in certain stages 
of existence, 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 Blod- 
sett, “the American climate is singularly extreme both in tem- 
Perature, humidity, quantity of rain, winds, and cloudiness or sen- 
ae humidity. The oscillations of the conditions are greater, 
“gg they vibrate through long measures above and below the 
Average. All the irregular as well as regular changes are of this 
1 Climatology of the United States, page 221. 
