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on the migration of birds. 
“ their motions with us by a failure of food, or by a propen- 
“ sity to moulting, or by a disposition to rest after so rapid 
“ a life, or by what? This is one of those incidents in Natural 
“ History that not only baffles our searches, but almost 
eludes our guesses l” Thus Mr. White. 
Now, should the principle I have laid down be admitted, 
namely, that these birds come here for scarcely any other 
purpose than to produce an offspring, and retreat when the 
task is finished, how easily will all circumstances be recon- 
ciled ? and how little mysterious will those things appear 
which naturally seemed unaccountable, not only to the ami- 
able author from whom the foregoing passage is taken, but 
also to others, who have written before on the same subject. 
It is somewhat remarkable, that so sagacious a philosopher 
as the illustrious and learned Ray, who so clearly saw the 
object of migration in fishes, should not also have been led 
to a sight of it in birds. After making a very just obser- 
vation respecting salmons, that quit the sea and ascend up 
rivers with no other view than to find a place of security for 
their spawn in the sand ; he directly says again, adverting to 
birds, “ What moves them to shift their quarters? You will 
“ say the disagreeableness of the air to the constitution of 
“ their bodies, or want of food.”* 
The spring migrating birds do not arrive here at first in 
very large numbers. It may be observed, that in the early 
part of April a few swallows may be seen ; soon after these 
a few solitary martins, and as the month advances now and 
then a swift. On the walls of Berkeley Castle, martins build 
their nests in great numbers. I availed myself of their situ- 
* Ray, on the Wisdom of God in the Creation. Part i., page 128. 
