288 FACULTIES OF BIRDS. 
rest and breed upon, and these are therefore com- 
monly called Gulrocks. Now if there be such glob- 
ules (or ethereal islands), they must be supposed of 
such magnitude only, and set off at such distance 
as their reflective light may not reach home to our 
earth (though perhaps they may serve to illuminate 
our atmosphere), else they would ere now have 
been discovered, and yet no farther off than these 
birds may conveniently arrive uato them in such 
time as may be most convenient to allow them. 
This I do suggest, because it is as hard for me to 
persuade myself that they come from any other part 
of this earth as it is to persuade another that they 
come from the moon; and, therefore, if the moon 
will not be allowed, some other place must be found 
out for them.”* 
This notion, extravagant as it appears to be, was 
discussed by the celebrated Ray and his correspond- 
ents; but, as might have been expected, it was de- 
cided by them that the moon is too far off to be 
reached by our migratory birds. 
Dismissing these untenable conjectures, we shall 
now state a few facts proving the migration of birds 
to other countries. 
In the Philosophical Transactions,} Catesby, who 
gave much attention to this subject, remarks, that, 
besides the migratory birds which remain and breed 
throughout the summer, there are others which ar- 
rive periodically at certain places, for the sake of 
some sort of grain or other food of which theirown 
country may be supposed destitute. These birds, 
after a short stay, depart, and are not again seen 
until that time twelvemonth, at which time they re- 
turn, and continue repeating their annual visits. 
Pursuing the subject, the same sensible naturalist, 
* An Essay towards the probable Solution of this Question, 
Whence come the Stork, &c. ; or where those Birds do proba- 
bly make their Recess, é&c., 12mo., Crouch, London, 1703. 
+ Vol. xliv., part i., for the year 1746. 
