THE ORBIT OF URANUS. 



105 



The next operation would be to interpolate these coordinates to intervals of 

 time suitable for the computation of a geocentric ephemeris, to correct the longi- 

 tudes for solar nutation, and then to compute the geocentric right ascension and 

 declination. This operation has not, however, been completely carried out except 

 for most of the observations before 1830, and for three of the oppositions observed 

 since, the latter being computed only as a check upon the accuracy of the com- 

 parisons. As a general rule, it may be said that wherever a complete geocentric 

 ephemeris, with the heliocentric ephemeris from which it was computed, were 

 available, these ephemerides were made use of in a manner Avhich will be more 

 fully described hereafter, while, in all other cases, the geocentric places Avere 

 computed directly. 



It may also be stated here that Hansen's Tables ilu Soleil have been adopted as 

 giving the places of the sun to be used in computing the geocentric places. 



U May, 1873. 



