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always fuppofed them to be fhort-fighted, as I never 
loft the fight of a bird myfelf, but from its horizontal 
diftance, and I doubt much whether any bird was 
ever feen to rife to a greater height than perhaps 
twice that of St. Paul’s crofs 
There feems to be but one method indeed, by 
which the height of a bird in the air may be efti- 
mated ; which is, by comparing its apparent fize with 
its known one, when very near us ; and it need not 
be faid that method of calculating muft depend 
entirely upon the fight of the oblerver, who, if he 
happens not to fee objedts well at a diftance, will very 
foon fuppofe the bird to be loft in the clouds. 
There is alfo another objedtion to the hypothefts 
of birds palling feas at fuch an extraordinary height, 
arifing from the known rarefaction of the air, which 
may poffibly be inconvenient for refpiratioo, as well 
as flight ; and if this was not really the cafe, one 
fhould fuppofe that birds would frequently rife to 
fuch uncommon elevations, when they had no oo- 
cafion to traverfe oceans,. 
* Wild geefe fly at the greateft height of any bird I ever 
happened to attend to ; and from comparing them with rooks, 
which I have frequently looked at, when perched on the crofs of 
St. Paul’s, I cannot think that a wi!d-goofe was ever diminifhed, 
to my fight at leaft, more than he would be at twice the height 
of St. Paul’s, or perhaps 300 yards. Mr. Hunter, F. R. S. in- 
forms me, that the bird which hath appeared to him as the higheft 
flier, is a fmall eagle on the confines of Spain and Portugal, 
which frequents high rocks. Mr. Hunter hath firft feen this 
fpecies of eagle from the bottom of a mountain, and followed it 
to the top, when the bird hath rifen fo high as to appear lefs 
than he did from the bottom. Mr. Hunter however adds, that 
Ire could ftill hear the cry, and diflinguilh the bird. 
The 
