ASTR 



OMICAL PAPERS, 



131 



To the American Philosophical Society, held at 



Philadelphia^ for promoting vjcful Knoivledge, 



GENTLEMEN, 



INCE my delivering in the iliort account of the im- 

 provement, which I propofed in the conftrudion of 

 Mr. Gocifreyh double refleding odaot, at a late meeting 

 of this fociety, I have been induced to fubjoin a relation 

 of the manner in which I was firft led into it, and of the 

 time when it was efFeded. In the beginning of the year 

 1767, finding that the common arch of the odant was too 

 fliort, for taking large anglesby afore obfervation,! thought 

 that it might be conveniently enlarged; and foon after 

 found that this enlargement might anfwer valuable pur-^ 

 pofes both at fea and on land. I communicated, to Mr, 

 Benjamin Condy^ mathematical inftrument-maker of this 

 city, my propofal for making the inftrument with double 

 the ufual arch, and the addition of a fecond fpeculum on 

 the index, inclined to the other in an angle of half the 

 length of the arch; as appears by his certificate, which I 



have here inferted in the following words, viz* 



w 



" nnmS is to urtify-i That fome time in thefpring or fi 

 -^ 7ner of the year 1767, the Revd. Mr. John Etvi 

 of this city-f communicated to me a propofal of his ^ fc 

 king Godfrey'* s Sextant ninth double the ifiial arch-^ and the 

 addition of another fpeculum qffir-''^ *- '^^" ;../.. ^^ ..=,7;,.^/;...,,7 



ving 



of half the enlarged arch ; am 

 frequently cowverfed together on the purpofc 



'liSlion. As %vit 



s 



defined to be anfwered by this nezv conf 



:/' 



fj L 



of J' 



770 



BENJAMIN COND T. ' ' 



About two years after I had thought of this conftrudion 

 of the inftrument and pcrfcded the dcmoaftration of it, 

 vv'hich I laid before the focicty on the original fcrap of pa- 

 per, on which it was firft written^ I learned by converfing 



with 



