392 British Association* 



acceleration of the Moon's motion, which is now exciting great 

 interest among mathematicians and physical astronomers. Prof. 

 Adams and M. Delaunay take one view of the question; MM. 

 Plana, Pontecoulant, and Hansen the other. Mr. Airy, Mr. Main, 

 the President of the Astronomical Society, and Sir John Lubbock 

 support the conclusions at which Prof. Adams has arrived. The 

 question in dispute is strictly mathematical ; and it is a very re- 

 markable circumstance in the history of Astronomy, that such 

 great names should be ranged on opposite sides, seeing that 

 the point involved is really no other than whether certain ana- 

 lytical operations have been conducted on right principles ; and 

 it is a proof, therefore, if any were wanting, of the extraordinary 

 complexity and difficulty of these transcendental inquiries. The 

 controversy is of the following nature: — Tne Moon's motion round 

 the Earth, which would be otherwise uniform, is disturbed by 

 the Sun's attraction; any cause therefore which affects the 

 amount of that attraction affects also the Moon's motion : now, 

 as the excentricity of the Earth's orbit is gradually decreasing, 

 the average distance of the Sun is slightly increasing every year> 

 and his disturbing force becomes less ; hence the Moon is brought 

 nearer the Earth, but at the rate of less than one inch 

 yearly, her gravitation towards the Earth is greater, and her 

 motion proportionably accelerated. It is on the secular 

 acceleration of the Moon's mean motion, arising from this minute 

 yearly approach, that the dispute has arisen ; so injfinitesimally 

 small are the quantities within the reach of modern analysis. Mr. 

 Adams asserts that his predecessors have improperly omitted the 

 consideration of the effect produced by the action of that part 

 of the Sun's disturbing force which acts in the direction of a tan- 

 gent to the Moon's orbit, and which increases the velocity ; his 

 opponents deny that it is necessary to take this into account at all. 

 Had not M. Delaunay, an able French analyst, by a perfectly in- 

 dependent process, confirmed the results of Prof. Adams, we should 

 have had the English and Continential astronomers waging war on 

 an algebraical question. On the other hand, however, the com- 

 putations of the ancient lunar eclipses support the views of the 

 Continent ; but if Mr. Adams's mathematics are correct, this only 

 shows that there must be other causes in operation, as yet undis- 

 covered, which influence the result ; and it is not at all unlikely, 

 that this most curious and interesting controversy will even- 

 tually lead to some important discovery in Physical Astronomy- 



