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ASTRONOMICAL AND NAUTICAL 

 COLLECTIONS. 



i. Simple Determination of the most ancient Epoch of 

 Astronomical Chronology, In a Letter to FRAficia 

 Baily, Esq., F.R.S. 



My dear Sir, 



When I addressed to you some remarks on the date of 

 an astrological manuscript, found in Egypt, I was not aware 

 how perfectly superfluous the chronological evidence, aflbrded 

 by such fragments, is rendered by the accuracy of the ori- 

 ginal tables of Ptolemy, which were probably the basis of 

 the computations that those fragments contain. I have since 

 looked into these tables, as they are exhibited in the edition 

 of Basil, which, without any suspicion of having been sophis- 

 ticated by translators or commentators, is still very cor- 

 rectly printed ; and my copy of which I read with the greater 

 pleasure, as a gift of my friend. Professor Schumacheh: 

 you have also had the goodness to furnish me with the elabo- 

 rate Commentaries of the Abb^ Halma, which I did not 

 venture to consult until I had made a separate computation 

 of the chief points that I wished to ascertain ; although I 

 afterwards obtained from them some valuable assistance in 

 verifying my results, and in the more ready comparison of 

 the different parts of the wonderful original with each other. 

 The planetary tables of Ptolemy are all carried back to 

 the epoch of the Alexandrian noon of the first day of the first 

 Egyptian year of the reign of Nabonassar. The mean daily 

 motion of Saturn, as laid down in these tables, is 0° 2' 0" 

 33'" 31"" 28'"" 51"""; and that of Jupiter 0° 4' 59" 14"' 26'"' 

 46'"" 31'""' ; (P. 214, 215, 217, 218.) The former of these 

 motions is less by -^f^iyi *^® latter by -x^(]o(t ^^b"? ^^^^ those 

 which are laid down by Bouvard in the latest of our modern 

 tables. They therefore afibrd very convenient foundations 

 for determining the exact year that was intended ; and their 

 evidence is of the more importance, as the other very slow 

 changes, which might be employed for the same purpose, 

 indicate, for some unknown reason, a much greater antiquity 



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