Summer Birds of Passage. 469 
‘pears upon an average, six days earlier at 
Stratton in lat. 52° 45’, than at Catsfield in 
lat. 51°. There is little or no doubt that this 
apparent exception to the present theory arises 
from some circumstances which retard the 
increase of the vernal temperature at Catsfield ; 
and make the spring advance more quickly at 
Stratton. As I am unacquainted with the 
situations of both places, it will be proper to 
state a few facts, which shew how powerfully 
causes of this sort influence the excursions of 
migrating birds. Ist. The bank | martin, 
(Hirundo riparia) is commonly seen at the 
mouth of the river Kent six or seven days 
before it arrives at Kendal; though the dis- 
tance does not exceed five or six miles. But 
the town lies near the mountains; and the 
air is colder in that part of the valley than at 
the head of the estuary. 2d. I have fre- 
quently heard the redstart, the yellow-wren, 
and the white-throat singing in the gardens 
at Kendal, two or three days prior to their 
arrival at Middleshaw. 1 attribute this differ- 
ence to the same cause; for Middleshaw lies 
200 feet higher than the town, being distant 
from it three miles to the south east. Lastly, 
the chimney-swallow was seen at Kendal on 
the 24th of April, A. D. 1808; but did not 
make its appearance at Settle, before the first 
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