Summer Birds of Passage. 4G5 
south to the north. Iam sorry, that the ob- 
servations are chiefly confined to the vege- 
table kingdom. The table, however, contains 
a remark, which is of importance to the pre- 
sent subject. For it traces the nightingale, 
afeeble bird of passage, through 22° of north 
latitude ; by assigning the times of its appear- 
ance on three distant parallels. Now it has 
been shewn, that the periodic birds do not 
remain torpid through winter, in those coun- 
tries which they frequeut in summer; conse- 
quently, we may infer with safety, that the 
nightingale travels leisurely towards the arctic 
circle during the vernal months, after leaving 
its winter retreat. which is unknown. In 
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, 
