320 Astronomy, [Lecture 20. 



angle increases; and from the rising of Libra 

 to the rising of Aries it decreases in the same 

 proportion. By this it appears that the ecliptic 

 rises fastest about Aries, and slowest about 

 Libra. On the parallel of London, as much of 

 the ecliptic rises about Pisces and' Aries in two 

 hours as the Moon goes through in six days ; 

 and therefore, while the moon is in these signs, 

 she varies but two hours in the time of her rising 

 for six days together; that is, she rises about 

 twenty minutes later every day or night than on 

 the preceding, at a mean rate. But in fourteen 

 days afterwards the Moon comes to Virgo and 

 Libra, which are the opposite signs to Pisces 

 and Aries; and then she differs almost four 

 times as much in rising ; namely, one hour and 

 about fifteen minutes later every day or night 

 than the former, while she is in these signs. 



The ecliptic, together with the fixed stars, 

 make 866^- apparent diurnal revolutions about 

 the earth in a year, the sun only 365^. There- 

 fore the stars gain three minutes fifty-six seconds 

 upon the sun every day ; so that a sidereal day 

 contains only twenty-three hours fifty-six mi- 

 nutes of mean solar time ; and a natural or solar 

 day twenty-four hours. Hence twelve sidereal 

 hours are one minute fifty-eight seconds shorter 

 than twelve solar hours. 



The sun advances almost a degree in the 

 ecliptic in twenty-four hours, the same way that 

 the moon moves ; and therefore the moon by 





