( X ) 
ator wliose works so loudly proclaim his wisdom, and tlie extent of his benevolence and attention to the innume- 
rable living objects which he has formed. 
§. XVIII. 
It is highly probable, that the periods of the migrations of birds will be found to be more or less uniform in pro- 
portion as the climates of the countries to which they migrate are more or less variable in their temperature. It is, 
perhaps, upon this principle, that we are to explain the difierence of the times of the arrival and departure of the 
birds of Pennsylvania, and other parts of North- America. The climates of these countries are extremely variable j 
I suppose more so than most other countries that are known to us. If, as has been supposed by many writers, the 
hand of man, by clearing and by cultivating the surface of the earth, contributes essentially to the greater uniformity 
in the temperature of climates, it is reasonable to conjecture, that the time will come, when the periods of the 
migrations of our birds will be more constant and fixed. For in North- America, especially the United-States, the 
progress of population, and of clearing and cultivating the earth, is more rapid and immense than in any other 
portion of the world. 
§. XIX. 
It would be a very curious subject of inquiry, — What changes have taken place in the periods of the arrival and 
disappearance of the passenger-birds, in those countries in which observations have long been made by the ancient! 
poets, and by naturalists ? Perhaps, an investigation of this question would, in some degree, illustrate the changes 
which climates are said to have undergone. Thus, the time of the Swallow's coming into Italy, is particularly 
mentioned both by Columella and by Pliny,* and it may be gathered also from a beautiful passage in the Georgics 
of Virgil.t Do the periods mentioned by these writers correspond with the periods of the arrival of this bird, in 
the same country, at present ? If the climate of Italy, within the last seventeen or eighteen himdred years, has 
altered as much as it is, by many ingenious men, thought to have done, it is not likely that the Swallow now visits 
that country at the same time it did formerly, in the days of Virgil, and the naturalists whom I have mentioned. I 
am sorry that I cannot, without some trouble, ascertain the question. 
§.xx. 
The fourth column of the tables will enable the curious naturalist to form some idea of the temperature of our 
climate (by showing the time of leafing, flowering, planting, &c. of a considerable number of vegetables, both 
native and foreign) ; at the same time, that it will point out, in a number of instances, the coincidence between 
this progress in vegetation and the arrival and disappearance of the migratory birds. This last has long been deemed 
an interesting subject by naturalists, though I am inclined to think, that they have often imagined, that this coinci- 
dence is greater than it really is. 
§. XXI. 
I will not deny, that there is a very remarkable conformity between the vegetation of some plants and the arrival 
of certain birds of passage. This, perhaps, is especially the case in those countries the climates of which are the 
most regular in their seasons. Linnaeus has observed, that the Wood- Anemone (Anemone nemorosa) blows in 
Sweden on the arrival of the Common Swallow, | and that the Marsh-Marygold (Caltha palustris) blows when the 
* Columella sayH, the Swallow Tisits Italy about the twentieth or twenty-third of February. The following are his own words: " Decimo Calendaf ! 
Martii leo dtrttnit occidere, vcnti septentrionaliiH, qui vocantur ornithiae, per dim triginta esse solent, turn et hirundo advenit." In another place, he says 6 
" Septimo Calendas Martii ventosa tempestas, hirundo conspicitur." De lie Ruelica. Pliny says, this bird appeared on the twenty-second of February II 
" Octavo calendaa Martii hirundinis visus." 
t Oeorgic. IV. 305—307. I Hirundo urbicn. I 
