24 Remarks on Ancient Eclipses. 



was in fact adding so many days to the Julian time, which clearly 

 demonstrates that the Julian time was too slow, and that aetro- 

 uomical time was by so m\\c\\ faster ; and therefore this numerical 

 adjustment vvas absolutely necessary, and safe from the more 

 known quantity of a solar year. 



10. The days of the week are however of that importance in 

 the computation of time, and especially long periods, that could 

 it be known for certain on what days of the week certain eclipses 

 of the sun and moon happened a century or many centuries ago, 

 or other events, it would help to determine more accurately and 

 positively the exact time, and greatly contribute to the perfection 

 of astronomy, chronology and history, and for this plain reason, 

 that the weekly cycle is as old as the creation, and is an account 

 of time kept up inviolably, not by a few isolated astronomers and 

 mathematicians, but preserved by the perpetual and unchange- 

 able custom of whole nations ! 



To illustrate the excellent method of computing time by the 

 cycle of weeksj I shall produce one example from the moon's 

 motion for one hundred years, where the terms of this period are 

 defined by the known days of the week. In the year 17 15, O. S., 

 April 22d, there happened a memorable eclipse of the sun on a 

 Friday: the middle of the eclipse vvas observed at fifty-one mi- 

 nutes after nine o'clock in the morning, which we will take for 

 the instant of the new moon. To correct this dale for the new 

 style it answers to May ^d, and from this date to May the 3d 

 IS 15, is one hundred years exactly. But the new moon which 

 happened in May 1815, according to the Ephemeris, was on 

 Tuesday the 9th day of the month, which by the cycle of weeks 

 is found to have hap])cned four days later than the cycle ending 

 on the Friday nearest to May o, 1815. Now it being impossible 

 that an error of a whole week can fall iuto this reckoniug for one 

 centurv, and the day of the week being known when the new 

 moon in April 1715 happened; and also the day of the week 

 when the corresponding new moon fell in May 1815, the calcula- 

 tion is indubitably certain without any possibility of error as 

 to the precise day aud number of days from one new moon to the 

 other. 



In 100 Julian years are 521 S weeks, less one day: therefore 

 from Friday April 22, 1715, to Friday May 5, 1815, are precisely 

 5218 weeks, or 36526 days, to which add the four days, and it 

 will bring it up to the new moon in May 1815, and the day of 

 the month and week as found in the Ephemeris, viz. Tuesday, 

 May the 9th, and the measure of time in days is 36530 ; but the 

 new moon in April 1715 was on Friday morning at fifty-one 

 minutes past nine o'clock, and that in May 1815, at twenty mi- 

 nutes 



