64 ASTRONOMICAL TABLES. SECT. VIII. 



greatest astronomers, from Newton to the present day, is only 

 successfully accomplished with regard to the older planets, which 

 revolve in nearly circular orbits, but little inclined to the plane 

 of the ecliptic. When the excentricity and inclination of the 

 orbits are great, their analysis fails, because the series expressing 

 the co-ordinates of the bodies become extremely complicated, and 

 do not converge when applied to comets and the telescopic planets. 

 This difficulty has been overcome by Sir John Lubbock, and other 

 mathematicians, who have the honour of having completed the 

 theory of planetary motion, which becomes every day of more 

 importance, from the new planets that have been discovered, and 

 also with regard to comets, many of which return to the sun at 

 regular intervals, and from whose perturbations the masses of the 

 planets will be more accurately determined, and the retarding 

 influence of the ethereal medium better known. 



