( X ) 
ator whofe works fo loudly proclaim his wlfdom, and the extent of his benevolence and attention to the innume* 
Table living objeds which he has formed* 
§. XVIII. 
It is highly probable, that the periods of the migrations of birds will be found to be more or lefs uniform in pro¬ 
portion as the climates* of the countries to which they migrate are more or lefs variable in their temperature. It is, 
perhaps, upon this principle, that we are to explain the difference of the times of the arrival and departure of the 
birds of Pennfylvania, and other parts of North-America. The climates of thefe countries are extremely variable ; 
I fuppofe more fo that mod other countries that are known to us. If, as has been fuppofed by many writers, the 
hand of man, by clearing and by cultivating the furface of the earth, contributes effentially to the greater uniformity 
m the temperature of climates,- it is reafonable to conjedlure, that the time will come, when the periods of the 
migrations of our birds will be more conflant and fixed. For in North-America, efpecially the United-States, the 
progrefs of population, and of clearing and cultivating the earth, is more rapid and immenfe than in any other 
portion of the world. 
§. XIX. 
It would be a very curious fubjedt of inquiry,—What changes have taken place in the periods of the arrival and 
difappearance of the paffenger-birds, in thofe countries in which obfervatrons have long been made by the ancient 
poets, and by naturalifls ? Perhaps, an invefligation of this queflion would, in fome degree, illuflrate the changes 
which climates are faid 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 alfo from a beautiful paffage in the Georgies 
of Virgil.f Do the periods mentioned by thefe writers correfpond with the periods of the arrival of this bird, in 
the fame country, at prefent ? If the climate of Italy, within the laft feventeen or eighteen hundred years, has 
altered as much as it is, by many ingenious men, thought to have done, it is not likely that the Swallow now vifits 
that country at the fame time it did formerly, in the days of Virgil, and the naturalifls whom I have mentioned. I 
am forry that I cannot, without fame trouble, afeertain the queflion. 
§. XX. 
The fourth column of the tables will enable the curious naturalifl to form fome idea of the temperature of our 
climate (^by flowing the time of leafing, flowering, planting, &c. of a confiderable number of vegetables, both 
native and foreign); at the fame time, that it will point out, in a number of inflances, the coincidence between 
this progrefs in vegetation and the arrival and difappearance of the migratory birds. This lafl has long been deemed 
an interefling fubjecl by naturalifls, though I am inclined to think, that they have often imagined, that this coinci¬ 
dence is greater than it really is. 
§. XXL 
I will not deny, that there is a very remarkable conformity between the vegetation of fome plants and the arrival 
of certain birds of paffage. This, perhaps. Is efpecially the cafe in thofe countries the climates of which are the 
mofl legular in their feafons. Linnasus has obferved, that the AVood-Anemone (Anemone nemorofa) blows in 
oweden on the ai rival of the Common Sw^allow,| and that the Marfh-Marygold (Caltha paluflris) blows when the 
* Columella fays, the Swallow vifits Italy about the- twentieth or twenty-third of February. The following are his own words: “ Decimo Calendas Martii lea 
definit occidere, vend fcptentrionalcs, qui vocantur ornithic, per dies triginta effe folent, turn et hirundo advenitd’ In another place, he fays, “ Septimo Calendas 
M-artu ventofa tempeftas, hirundo coufpicitur.” ^ De R, Rujlka, Pliny fays, this bird appeared on the twenty-fecond of February : » Oftavo calendas Martii hirun- 
dinis vifus.” 
t Georgic. IV. 30J—307. J Hirundo urbica. 
N 
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