ASTRONOMY. 109 



Suppose, for example, that 365<i -f - R= , a re^- 



volution of the sun ; then 



4x365 + 1=4- R = 3X 365 + 366^ so that if we 

 count three years, each of 365 days, and a fourth 

 of 366, we shall have exactly four revolutions of 

 the sun ; and at the beginning of the fifth year, the 

 sun will be in the same point of the ecliptic which 

 he was in at the beginning of the first. This is the 

 arrangement of what is called the Julian Kalen^ 

 dar ; and if the revolution of the sun were exact- 

 ly 365d 6h, it would be altogether perfect, It is 

 called the Julian Kalendar, and the Year thus 

 computed, the Julian Year, from JULIUS CAESAR, 

 by whom, with the advice of the astronomer So- 

 SIGENES, it was introduced at Rome. 



The addition of a day, or a number of days, to any 

 fixed period, at stated intervals, is called Interca- 

 lation. The year on which the intercalation fell 

 was called Bisscxtilis, because the 6th of the Ka- 

 lends of March was twice counted. With us, it 

 is called Leap year. 



As the true length of the sun's revolu- 

 tion is not what has now been supposed, but in- 

 stead of 365 d .&5, is only 365 d .242264, the Julian 

 year is longer than the revolution of the sun by 

 O d .007?36, (nearly ll m ) ; and, therefore, before 

 a new year begins, the gun has passed the point 



in 



