ASTRONOMY* 91 



Apparent Orbit of the Sun. 



92. If the sun's motion in the ecliptic be de- 

 termined by observation from day to day, 

 ( 81. #.), it will be found, that it is not uni- 

 form, but is swiftest about the beginning of Ja- 

 nuary, and slowest about the beginning of July ^ 

 being continually retarded from January to July, 

 and accelerated from July to January. 



93. If the apparent diameter of the sun be al- 

 so observed every day by a micrometer, or any 

 instrument that measures small angles with 

 great exactness, it is found to vary, so as to be 

 greatest when the angular motion is greatest, 

 and least, when it is least. The angular velo- 

 city, and the diameter of the sun, do not, how- 

 ever, vary in the same ratio ; but the angular 

 velocities, at any two points of time, are as the 

 squares of the apparent diameters. 



Thus, if v and t/ are the angular velocities of the sun, 

 or his diurnal advances in the ecliptic, at any two 



seasons- 



