428 LECTURE XLV. 



commonly called by astronomers the year 0, but by chronologists the year 

 1 before Christ. The correction introduced by Caesar was, however, too 

 great, the error being exactly 7 days in 900 years ; so that in 1582 it 

 amounted to about 12 days. This error was not wholly removed by Pope 

 Gregory, who reformed the calendar ; he omitted 10 days only of the usual 

 reckoning, in order to bring back the course of the moveable feasts to the 

 same state, in which they had been established by the Nicene council, in 

 the fourth century. He determined at the same time that the last year 

 of every century should be passed without an intercalary day, excepting 

 that of every fourth century, which was still to be bissextile. Thus every 

 year divisible by four, without a remainder, is in general a bissextile or 

 leap year, but the last year of every century must be a common year, 

 unless the number of the century be divisible by 4 ; the year 1800 being 

 a common year, and 2000 a bissextile. In this manner 27 Julian bissex- 

 tiles are omitted in 3600 years, while the true length of the year would 

 require the omission of 28 ; but so small a difference can be of no material 

 consequence. The Persians had introduced into their calendar, in the 

 llth century, an intercalation still more accurate ; they make 8 bissex- 

 tiles only every 33 years, reckoning four common years together instead 

 of three, at the end of this period, so that in 132 years they have 32 leap 

 years instead of 33 ; and the error is only a day in about five thousand 

 years. If any change in the Gregorian calendar were thought necessary, 

 it would be easy to make the last year of every fourth and fifth century 

 alternately a bissextile, and this correction would be quite as accurate as 

 it is possible for our calculations to render it. The adoption of the 

 Gregorian calendar in this country was for some time delayed by religious 

 prejudices ; one of the best-founded objections to it was, that 2 days of 

 the real error was still unconnected ; but better arguments at last over- 

 came these difficulties, and the new style was introduced on the 14 Sep- 

 tember 1754, which would have been called, according to the old style, the 

 third. 



Any tolerable approximation of this kind, when once generally estab- 

 lished, appears to be more eligible than the mode which was lately adopted 

 in France, where the republican year began at the instant of the midnight 

 preceding the sun's arrival at the autumnal equinox. Mr. Lalande very judi- 

 ciously observes, that there are several years, in which the sun will pass the 

 equinox so near to midnight, that it is not at present in the power of calcu- 

 lation to determine on what day the republican year ought to begin ; and 

 perhaps these arguments have co-operated with others in facilitating the 

 restoration of the ancient calendar. 



The revolutions of the sun and moon are not very obviously commen- 

 surable, the solar year containing 12 lunations and almost 11 days ; but 

 Meto discovered, more than 2000 years ago, that 19 solar years contain 

 exactly 235 lunations ; and this determination is so accurate, that it makes 

 the lunar month only about half a minute too long. Hence it happens, 

 that in every period of 19 years, the moon's age is the same on the same 

 day of the year. The number of the year, in the Metonic cycle, is called 

 the golden number, the calendar of Meto having been ordered, at the cele- 



