160 NATURAL HISTORY 
tions of the difference between the present temper 
ature of the air in Italy,” &c., have fallen in my 
way, and gave me great satisfaction. They have 
removed the objection that always arose in my 
mind whenever I came to the passages which you 
quote. Surely the judicious Virgil, when writing 
a didactic poem for the region of Italy, could never 
think of describing freezing rivers, unless such se- 
verity of weather pretty frequently occurred! | 
P.S.—Swallows appear amid snows and frost. 
> 
LETTER Vite 
Selborne, May 21, 1770. 
Dear Sir,—THueE severity and turbulence of last 
month [ April] so interrupted the regular process of 
summer migration, that some of the birds do but 
just begin to show themselves, and others are ap- 
parently thinner than usual; as the whitethroat, the 
blackcap, the redstart, the fly-catcher. I well re- 
member, that after the very severe spring, in the 
year 1739-40, summer birds of passage were very 
scarce. They come probably hither with the south. 
east wind, or when it blows between those points ; 
but in that unfavourable year the winds blew the 
whole spring and summer through from the opposite 
quarters. And yet, amid all these disadvantages, 
two swallows, as | mentioned in my last, appeared 
this year as early as the 11th of April, amid frost 
and snow, but they withdrew again for a time, 
I am not pleased to find that some people seem 
so little satisfied with Scopoli’s new publication.* 
* This work he calls his “ Annus Primus Historico-Naturalis,” 
