The GEORGIUM SIDUS. 3 n 



964 of MAYER, near half a century muft elapfe before the ele- 

 ments of its motion can be determined with a precifion equal 

 to that which is attained in the cafe of the other Planets. But 

 the method affigns certain limits, and thefe not very wide, with- 

 in which all the circumftances of its motion muft be compre- 

 hended. This alone muft be regarded as a confiderable attain- 

 ment. 



THE heliocentric place of the Planet in oppofition to the Sun, 

 on the 2 1 ft of December 1781, was determined by me, from 

 obfervations made on the i9th and 28th of that month, by 

 Dr MASKELYNE, combined with obfervations made by Profef- 

 for SLOP at Pifa, on the 22d, 23d, 27th, and 28th. The helio- 

 centric place at the oppofition 1782, was determined from ob- 

 fervations made by Dr MASKELYNE on the I4jth and 28th of 

 December, combined with thofe of Profeflbr SLOP on the 22d, 

 25th, and 26th of that month. The place of oppofition in 

 1783 was determined from my own obfervations on the 26th, 

 27th, 28th of December, and the jth of January following. 

 The place at oppofition January 3d 1 785, was determined from 

 my own obfervations on the 28th and 2Qth of December, and 

 the i ft and 6th of January. The place at oppofition 1786, 

 was determined from my own obfervations on the 29th, 3oth 

 and 3ift of December, and the ift, 3d, and 8th of January. 

 The method which I took for combining thefe obfervations, in 

 order to get rid of the inaccuracy to which each of them was 

 liable, was as follows : The arch described between any two 

 fucceflive oppofitions gave me a pretty near approximation to 

 the diftance of the Planet from the Sun, by means of the Kep- 

 lerian~law, that the fquares of the angular motions are inverfe- 

 ly as the cubes of the diftances. The heliocentric angular 

 motion, at any oppofition, muft be very nearly a medium be- 

 tween the angular motions with which the arches, intercepted 

 between it and the preceding and following oppofition, would 

 be uniformly defcribed. Thus I obtained, with fufficient ac- 

 curacy, 



