Remarks on Avdc7it Eclipses. 345 



8. The falling back of the conjunctions of the sun and moon 

 one dav in 304 vears, or three days in 912 years, extends the 

 great lunar period to 120 periods of 912 years, or upwards of 

 100,000 years, which is an unbounded length; and however 

 enormous this may appear, yet an author since Mr. Ferguson 

 has calculated the grand lunar period at 7,948,800 synodical re- 

 volutions, or more than 600,000 years, to go through all her va- 

 riations and complete her cycle. Mr. Ferguson, it must be al- 

 lowed, was more decent when he assigned the very moderate 

 period of 12,492 years ! See his Astronomy, art. 321, p. 245. 

 All this arises from our imperfect knowledge of the lunar theory. 



9. If my positions are true, the entire revolutions of the moon 

 arc limited to the period of 912 solar years, in which time her 

 relative motions with the sun, and the whole phaenomena of 

 eclipses, are completed. The very supposition of enlarging this 

 period by any supposed anticipation of either sun or moon be- 

 yond this period, produces nothing but doubt, uncertainty, and 

 useless speculation. 



10. The reform of the calendar in different ages may in some 

 cases affect the true dates of ancient eclipses ; but 1 cannot dis- 

 cover that even the reform of the calendar in the age of the 

 Nicene Council has at all affected the dates of the eclipses prior 

 to that period, nor subsequent thereto, until the time of Pope 

 Gregory, and the introduction of the New Style. 



11. It appears from the ancient writers, that the memorable 

 year commencing the sera of Nabonasser 747 years before Christ 

 was a famed astronomical epoch, when the Babylonian and 

 Egyptian calendars coincided with the ecpiiuoctial points ; con- 

 cerning which Dr. Keill remarks, Astron. Lectures, xxvii. p. 3(i7: 

 " The aera of Nabonasser," says the learned Professor, " has al- 

 ways been famous among astronomers, and began on the sixth 

 of Februarv of the Julian year carried backward, and before Christ 

 7^7 years : and because that day was then the first of the Egyp- 

 tian year, Ptolemy and after him Copernicus computed the mo- 

 tions of the stars according to that aera by Egyptian years." 



12. If we compute the difference of the .Julian and solar rec- 

 koning from the said epoch, at the rate of eleven minutes per 

 annum to the date of any eclipse, and add thereto seven whole 

 davs for one period afterwards, we shall reduce those Julian dates 

 to the true solar account ; and by another equation, viz. sub- 

 tracting four days for any period amounting to seven days, or 

 fourteen days for two periods : by these two simple equations we 

 shall be enabled to reduce all the above ancient eclipses to an 

 harmony with the modern tables with a surprising exactness. 



To reduce the date of the eclipse of the sun observed by the 



Chinese astronomers twenty-four years before the Christian aera, 



Vol. 55. No. 2G5. May 1S20. F f see 



