130 THE NATURAL HISTORY 



Some extracts from your ingenious " Investigations of 

 the difference between the present temperature of the air 

 in Italy," etc., have fallen in my way ; and gave me great 

 satisfaction : they have removed the objections that 

 always rose 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 

 severity of weather pretty frequently occurred 1 



P.S. Swallows appear amidst snows and frost. 



LETTER VI 



Selborne, May 21, 1770. 

 Dear Sir, 



The severity and turbulence of last month so inter- 

 rupted the regular progress of summer migration, that 

 some of the birds do but just begin to show themselves, 

 and others are apparently thinner than usual ; as the 

 white-throat, the black-cap, the red-start, the fly-catcher. 

 I well remember that after the very severe spring in the 

 year 1739-40 summer birds of passage were very scarce. 

 They come probably hither with a south-east wind, or 

 when it blows between those points ; but in that unfavour- 

 able year the winds blowed the whole spring and summer 

 through from the opposite quarters. And yet amidst all 

 these disadvantages two swallows, as I mentioned in my 

 last, appeared this year as early as the eleventh of April 

 amidst 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 ; * there is 



* This work he calls his Annus Primus H islorico-Naturalis. 



