1XX REPORT— 1860. 



Sir John Lubbock support the conclusions at which Professor Adams has 

 arrived. The question in dispute is strictly mathematical ; and it is a very 

 remarkable 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 analytical operations have been conducted on 

 right principles ; and it is a proof therefore, if any were wanting, of the extra- 

 ordinary complexity and difficulty of these transcendental inquiries. The 

 controversy is of the following nature : — The 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 is 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 infinitesimally 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 tangent 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 independent pro- 

 cess, confirmed the results of Professor Adams, we should have had the 

 English and Continental Astronomers waging war on an algebraical question. 

 On the other hand, however, the computations 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 

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

 this most curious and interesting controversy will eventually lead to some 

 important discovery in Physical Astronomy. 



You are aware that at the suggestion of Sir John Herschel an instrument 

 was constructed for the Kew Observatory, to which the name of Photohelio- 

 graph has been given, because it is adapted solely to the purpose of obtaining 

 photographic representations of the appearances on the Sun's disc. Many 

 difficulties have been encountered in the use of this instrument, but by the 

 zealous exertions of the late Mr. Welsh, Mr. Beckley, and Mr. De la Rue, 

 they have been overcome. It is to the last-named gentleman, so distinguished 

 for his successful prosecution of celestial photography, that the Royal Society 

 have entrusted a grant of money to enable him to transport the Photohelio- 

 graph to Spain, to observe the total eclipse of the Sun, which is now 

 approaching, and great interest will attach to records of the phenomena of 

 the eclipse thus obtaiued. 



In Chemistry I am informed that great activity has been displayed, espe- 



