XI. fbe ORBIT and MOTION of the GEORGIUM SIDUS 

 determined direHly from Obfervations, after a very eafy and 

 ftmple Method. By JOHN ROB I SON, M. A. F. R. S. ED IN. 

 and ProfeJJor of Natural Philofopby in the Univerjity of 

 EDINBURGH. 



{Read by the Author^ March 6. 1786.] 



TH E accuracy of modern obfervations has difcovered irre- 

 gularities in the motions of Jupiter and Saturn, which 

 our knowledge of the laws of planetary gravitation has not as 

 yet enabled us to explain. I have, therefore, long thought it 

 probable that there may be planets without the orbit of Saturn, 

 of fufficient magnitude to occafion thefe irregularities. This 

 conjecture is confirmed by the difcoyery of a new planet. 



ON the i3th of March 1781, Mr HERSCHEL, an aftronomer 

 of great ardour and ingenuity, obferved a Star, near the foot of 

 Caftor, whofe fteady light attracted his attention. He immedi- 

 ately applied to his telefcope a higher magnifying power, and 

 difcovered an augmentation of its apparent diameter. Two 

 days after, he obferved that it had changed its place ; and, 

 taking it for a comet, he wrote an account of his obfervation 

 to Dr MASKELYNE, Aftronomer-royal, who got fight of this 

 Star on the i7th of March. An account of this difcovery was 

 foon given to the other aftronomers of Europe, who have con- 

 tinued to obferve it with unceafing attention. I did not obtain 

 a fight of it till Auguft 1782. 



ALMOST at its firft appearance, the Englifh aftronomers fup- 

 pofed it to be a Planet. They were led to this opinion by va- 

 rious circumftances which rendered it very probable j fuch as, 



Qjl its 



