BIRDS OF PASSAGE. 
205 
pace with the diffusion of solar heat over the northern half of 
the globe. For the same plants flower much earlier in low 
than in high latitudes ; and we may safely conclude that the 
same lethargic animals, especially the same flies and other 
insects, will observe the like rule in quitting their winter 
quarters ; and will appear abroad in Italy much sooner than in 
Britain. The following comparative facts may serve to elucidate Facts relatival 
the slow progress of spring from the south to the north. I am to the progress 
r or spring, 
sorry, that the observations are chiefly confined to the vegetable 
kingdom. The table, however, contains a remark, which is of 
importance to the present subject. For it traces the nightingale, 
a feeble bird of passage, through 22° of north latitude $ by 
assigning the times of its appearance on three distant parallels. 
Now it has been shewn, that the periodic birds do not remain Birds migrate 
torpid through winter, in those countries which they frequent leisurely from 
in summer $ consequently, we may infer with safety, ihat the 
nightingale travels leisurely towards the arctic circle during the 
vernal months, after leaving its winter retreat, which is unknown. 
Jn this long journey, this bird passes from one degree of 
latitude to another, as the advances of spring prepare the 
successive climates of the northern hemisphere for its reception, 
by warming the ground, and calling the insects of each country 
progressively into active existence. 
clime to clime. 
The Progress of Spring shewn by the Time of flowering of the 
same Plants in different Latitudes. 
Name. 
Athens, 
lat.37°25' 
Stratton, 
lat .5V°4b' 
Kendal, 
lat.54 n 26' 
Upsal. 
iat.59°36' 
TiPHFfliiini vprnnm t 
Feh. 1 
Feb. 5 
Feb. 14 
Feb. 16 
Mar. 2 
Mar. 24 
April 13 
May 15 
Narcissus pseudo-Narcissus. f. . 
April 10 
April 10- 
April 22 
Mar. 22 
Ulmus campestris. v 
Crataegus Oxyacantha. v. . . . 
Nightingale sings. ....... 
April 15 
May 15 
May 15 
May 15 
This 
