( 1 8* ) 
I. A Propofal of a Method for finding the Longi- 
tude at Sea within a Degree , or twenty Leagues. 
<By Dr. Edmund Halley, Aftr. Reg. Vice - 
[ Vrefident of the Royal Society. With an Ac- 
count of the Progrefs he hath made therein , by a 
continued Series of accurate Obfervations of the 
Moon, taken by him/elf at the Royal Obfer- 
vatory at Greenwich. 
I T is now above twenty Years fince I added an 
appendix to the fecond Edition of Mr. Street's 
Caroline Tables , containing a Set of Obfervati- 
ons I had made in the Years 1 68 3 and 1684, for af- 
certaining the Moon’s Motion ; and giving a .Specimen 
of what I thought, at that Time, might be the only 
pradicable Method of attaining the Longitude at Sea. 
What I printed fo long ago, is as follows: 
« c The Advantages of the Art of finding the 
“ Longitude at Sea, are too evident to need any Ar- 
« guments to prove them. And having by my own 
“ Experience found the Impradicability of all other 
“ Methods propofed for that Purpofe, but that deri- 
“ ved from a perfeQ: Knowledge of the Moods Moti - 
“ on ; I was ambitious, if poflible, to overcome the 
“ Difficulties that attend the Difcovery thereof. 
“ And firft, I had found it only needed a little 
“ Pradice to be able to manage a five or fix Foot Te- 
“ lefcope, capable of fhewing the Appulfes or Occulta- 
u tions of the Fix'd Stars by the Moon , on Ship- 
“ board, in moderate Weather ; efpecially in the Firft 
B b “ and 
