516 BIOGRAPHICAL ACCOUNT 



named in it as a New Society, which, as its first act, united to 

 itself the whole of the Philosophical. 



Professor Robison, one of those named in the original char- 

 ter, was immediately appointed Secretary, and continued to 

 discharge the duties of that office, till prevented by the state of 

 his health several years after. 



The first volume of the Transactions of this Society, con- 

 tains the first paper which Professor Robison submitted to the 

 public, a " Determination of the Orbit and the Motion of the 

 " Georgium Sidus, directly from Observations," read in March 

 1786. This planet had been observed by Dr Herschell on 

 the 13th March 1781, and was the first in the long list of dis- 

 coveries by which that excellent observer has for so many 

 years continued to enrich the science of Astronomy. Its 

 great distance from the sun, and the slowness of its angu- 

 lar motion, which last amounts to little more than four de- 

 grees from one opposition to the next, made it difficult to de- 

 termine its orbit with tolerable accuracy, from an arch which 

 did not yet exceed an eighteenth part of the whole orbit. 

 This was an inconvenience which time would remedy ; but 

 impatience to arrive even at such an approximation as the 

 facts known will afford, is natural in such cases, and Pro- 

 fessor Robison, as well as several other mathematicians, were 

 not afraid to attempt the problem, even in this imperfect state 

 of the data. It is well known that the observations which best 

 serve the purpose of determining the orbit of a planet, are 

 those made at its oppositions to the sun, when an observer in 

 the Earth and in the Sun would refer the planet to the same 

 point in the starry heavens, or when, in the language of astro- 

 nomers, its heliocentric and geocentric places coincide. Of 



these 



