102 OUTLINES OF NATURAL PHILOSOPHY. 



103. Astronomical tables, constructed from 

 the data, and on the principles now explained, 

 serve to determine the sun's place in the eclip- 

 tic, for any instant of time, either past or fu- 

 ture. 



a. From the time of the sun's passing through the pe- 

 rigee, when the true and mean place coincide, the 

 mean place for any other time may he computed, 

 by allowing for the interval an increase of longi- 

 tude, at the rate of 59' 8".3per diem, and thus the 

 mean anomaly is computed. From the mean ano- 

 maly, is found the equation of the centre, con- 

 tained in a table, which gives the quantity of that 

 equation for every degree of mean anomaly; thence 

 is given the true anomaly, and of course the true 

 longitude. The tables are so constructed, as to 

 give the mean place of the sun for the beginning 

 of every year ; hence the mean place for any time 

 of any year is easily found. When equations are 

 thus ranged in tables, the quantity by which they 

 are found out in the table, and on which their 

 magnitude depends, are called the Arguments of 

 the Equations. 



The tables of the sun's motion, are in reality nothing 

 else than the expansion of the general formula 

 contained in 100. 



b. Thus, from the fact of the variation of the sun's ap- 

 parent diameter, compared with the variation of 

 the angular velocity of the same body, it is demon- 

 strated, 



