On ihf: Magminde oj theYear. 17 



D. H. M. " 



1. Hipparchus .. .« ,. 365 5 55 16 



2. Ptolemy 365 5 55 12 



3. R. Adda 365 5 55 25 26" 20'" 



4. Copernicus' greatest\ ^ ^ 355 5 55 37 4 



magnitude . . . . J 



5. Prutenic Tables, ditto .. 365 5 55 53 



6. Chr.Sev.LongomontanuSjT o/>r r ri nq 19 



ditto . . J 



7. David Organus, ditto . . 365 5 56 53 



The Copernicans distinguished a greatest, mean, and least 

 measure for the solar year, according to which the solar vears 

 are either of various quantities, or else no certain quantity was 

 certainly discoverable by them common to them all. 



It is well known that the lunar year makes an entire revolu- 

 tion, and moves through all the seasons, in 33 years ; in like 

 manner the solar year is supposed to revolve at the extremely 

 slow progress of 50" per annum, and in 25412 years complet- 

 ing its motion through the great circle of the heavens ; and this 

 opinion still prevails in the modern astronomy, and will until 

 the theory of the celestial motions be better understood. 



The Julian calendar preserves a mean between the solar and 

 sidereal year ; and hence it is that this calendar is made the 

 .standard measure of time among astronomers ; so that bv sup- 

 pressing a certain number of days in a long period of years, the 

 solar year is regulated by the seasons; and by adding a certain 

 number of days the sidereal years, are conveniently ascertained, 

 which regulation of time constitutes the principle of the Gre- 

 gorian calendar. 



The Julian calendar constantly adds one day in four years ; 

 and because this reckoning in a great number of years is not 

 found to keep to the seasons, therefore the Gregorian calendar 

 suppresses three days in four hundred years, that so the equinoc- 

 tial days in the calendar may fall on the true equinoctial days of 

 the sun. 



In 912 Julian years are 47586 weeks, and 6 days; and in 

 912 solar years are 4/585 weeks, and 6 days: so that the dif- 

 ference between the calendar Julian and Gregorian account is 

 one week. In this period one minute less or more in the quan- 

 tity of a solar year will make a difference of fifteen hours, twelve 

 minutes; and one second, less or more, will amount to fifteen 

 minutes, twelve seconds ; according to which the following table 

 is constructed for the various (juantities assigned for the solar 

 year, and the anticipation of time in days for 912 years. 



Vol. 57. No. 273. Jan. 1821. C Calippus. 



