ASTRONOMY, 



the sun's equinoctial station precede the usual cal- 

 culation. The precession is equal to =50"- annu- 

 ally moving westward. 



Exact Length of the Year. 



When two equinoxes at the distance of 60 years 

 were observed, the interval was found to be nearly 

 21,000 days. 



The exact length of the year is 365 days, 5 hours, 

 48 minutes, 51 seconds, 6 decimals. 



An astronomer thinks he commits no error, when 

 he considers the rate of the sun's motion as uniform 

 (which in reality it is not) for 24 hours. 



The Earths Annual Revolution an Uncertain Measure 

 of Time. 



Notwithstanding the earth's annual revolution 

 round the sun we cannot ascertain its real duration 5 

 for although this should continue for 365J days 

 without change, every day, every hour, and every 

 second may be proportionally shorter, without our 

 being able to discover it. La Place computes that 

 since the time of Hipparchus, the year has become 

 some few seconds shorter. Possibly the change was 

 greater at first, diminishing as the earth's orbit, ap- 

 proached a true circle. 



The Relative Length of the Seasons. 



M. Biot endeavoured to show how the position 

 of the Apsides affects the relative length of the sea- 

 sons thus 



