ADDRESS. lxix 



which it has consistently discharged the task imposed upon it by its founder 

 and those who inaugurated its first proceedings. The duty assigned to it 

 was " to rectify the tables of the motions of the heavens and the places of 

 the fixed stars, in order to find out the so much desired longitude at sea, for 

 perfecting the art of navigation ;" and gloriously has it executed its task. 

 For two centuries it has been at work, endeavouring to give to the determi- 

 nations of the places of the principal fixed stars and of the heavenly bodies 

 of our own solar system, and more especially of the Moon, the utmost degree 

 of precision ; and during the same period, the master minds of Europe have 

 been engaged in perfecting the analytical theory, by which the many and 

 most perplexing inequalities of the Moon's motion must be accounted for 

 and represented, before Tables can be constructed giving the place of our 

 satellite with that accuracy that the modern state of science demands. 



The very important task of calculating such Tables has just been finished. 

 Our able and accomplished Director of the National Observatory, Mr. Airy, 

 had caused all the observations of the Moon made at Greenwich, from 1750 

 to 1830, to be reduced upon one uniform system, employing constants 

 derived from the best modern researches ; and a distinguished Danish Pro- 

 fessor, who had been for some time engaged in calculating new Tables of the 

 Moon, availed himself of the data so furnished. Professor Hansen happily 

 brought to his task all the accomplishments of a practised observer, and of 

 one of the most able analysts of modern times, combined with the most 

 determined industry and perseverance. In the completion of it he was 

 liberally assisted by our Government, at a time when an unhappy war had 

 deprived the Danish Government of the means of further aiding their Pro- 

 fessor, and a great astronomical work had been suspended for want of £300, 

 a sum which many do not hesitate to spend on the purchase of some, useless 

 luxury. Professor Hansen's Tables are now finished and published. They 

 agree admirably with the Greenwich Observations with which they have 

 been compared, and the mode of their execution has been approved by those 

 competent to express an opinion on such a subject. They have been 

 rewarded also with the Gold Medal of the Astronomical Society, a distinction 

 never lightly bestowed. 



In paying this tribute to the merit of Professor Hansen, I must not be 

 understood as wishing to ignore, far less depreciate, that of three very emi- 

 nent geometers — Plana, Lubbock, and Pontecoulant, who have devoted 

 years of anxious and perhaps ill-requited labour to the investigation of the 

 Lunar inequalities, but who have never yet embodied the results in the only 

 form useful to Navigation, that of Tables. 



A curious controversy has lately arisen on the subject of the acceleration 

 of the Moon's motion, which is now exciting great interest among mathe- 

 maticians and physical astronomers. Professor Adams and M. Delaunay 

 take one view of the question ; MM. Plana, Pontecoulant, and Hansen the 

 other. Mr. Airy, Mr. Main the President of theAstronomical Society, and 



