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always fuppofed them to be (Bort-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 y which is, by comparing its apparent fize with 

 its known one, when very near us - x and it need not 

 be faid that method of calculating muft depends 

 entirely upon the fight of the obferver,. who, if he 

 happens not to fee objects well at a diftance, will very 

 ibon fuppofe the bird to be loft in the clouds. 



There is alfo another objection to the hypothecs - 

 of birds paffing feas at fuch an extraordinary height^ 

 arifing from the known rarefaction of the air, which 

 may poffibly be inconvenient for refpiration, ..as wellh 

 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 oc«*~ 

 eafion 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 wild-goofe was ever dimimfhed^ 

 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 fir ft- 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 

 he could ftill hear the cry, and diftinguiih the bird. 



The 



