279 



kept for ever in their apartments in Somerset House. And I hereby 

 dedare that my will and intention as to the arrangement of the 

 memoirs, engravings, drawings, autographs, books, the gold watch 

 formerly belonging to Sir Isaac Newton, the gems and other relics 

 of which the said ' Collectanea ' is composed, is expressed in a ma- 

 nuscript catalogue, which will be found in the box containing the 

 collection, and signed by me. But it is not my intention that the 

 plan therein described should be strictly adhered to, if the President 

 and Council prefer any other method with regard to the arrange- 

 ment of the work. 



" And I hereby direct my executors to pay the above legacy within 

 three months after my decease ; and if two hundred pounds should 

 not be sufficient for the purposes before mentioned, then my exe- 

 cutors are hereby required and empowered to advance fifty pounds 

 more (free of legacy duty) ; and if there should be any overplus in 

 either case, then the President and Council of the said Society are 

 at liberty to apply such overplus in the purchase of books for the 

 Library, or in any other way for the benefit of the Royal Society." 



The reading of Mr. Airy's paper, entitled " On the Eclipses of 

 Agathocles, Thales and Xerxes," was resumed and concluded. 



The author, after remarking that the calculations of distant eclipses 

 made in the last century possess little value, proceeds to give the 

 successive steps of improvement in the lunar theory as applicable 

 to tiie computation of eclipses, and especially in the motion of the 

 moon's node. The first great improvement was the introduction by 

 Laplace of terms expressing a progressive change in the mean secu- 

 lar motions. With Burg's tables, in which these changes were in- 

 troduced, or with the same elements, Mr. Francis Baily and Mr. 

 Ottmanns computed many eclipses in the search for that usually 

 called the eclipse of Thales ; and both these astronomers fixed upon 

 the eclipse of b.c. 610, September 30, as the only one which could 

 be reconciled with the account of Herodotus. Mr. Baily however 

 subjoined a computation of the eclipse of Agathocles from the same 

 elements, and found that this could not by any means be reconciled 

 with the historical account ; he inferred from this that some serious 

 change in the theory is necessary, and that when it was introduced 

 the eclipse of b.c. 610 might not be found to agree with history; 

 but he thought it certain that no other eclipse could be adopted. 

 The various values of the motion of the node adopted by different 

 writers from different observations (principally total or annular 

 eclipses) are then collected. Allusion is then made to the peculiar 

 value of the eclipse of Stiklastad (brought to notice by Professor 

 Hansteen), and which will be increased when the calculations shall 

 have been made on unexceptional elements. The author then ad- 

 verts to the great Reduction of the Greenwich Observations from 

 1750 to 1830, to Hansen's new inequalities, and to the numerical 

 amounts of corrections of the principal elements. Then are given 

 the coefficients of the change in secular value of mean motion of the 

 mean of the moon's perigee, and of the moon's node, as found by 



