220 Royal Society. 



In the short Treatise upon the Attraction of Spheroids which con- 

 stitutes the second part of this tract, the author has endeavoured to 

 treat that subject in as elementary a manner as possible. He has 

 made continual references in it to the authors who have written upon 

 the figure of the earth : it may serve therefore, in some measure, to 

 illustrate the first chapter in the fifth volume of the Mecunique Celeste. 

 He shows, in the Preface, that the first addition to the Newtonian 

 theory of the figure of the earth was made, not by Clairaut, as af- 

 firmed by Laplace, but by our countryman Stirling, in his paper "Of 

 the Gravity of the Earth,' and the Variation of Gravity on the Sur- 

 face," which was published in the Philosophical Transactions for 

 1735, two years prior to the appearance, in the same collection, of 

 the memoir in which Clairaut proved the approximate expressions 

 which Stirling (as evinced in his paper) must already have been in 

 possession of. The investigation of the latter, Mr. Lubbock thinks, 

 is a great addition to what is contained in the Principia. 



The following are the contents of this treatise : — Attraction of a 

 prolate spheroid upon a particle within it— Attraction of an oblate 

 spheriod upon a particle within it— Attraction of an ellipsoid upon a 

 point within it — Attraction of an ellipsoid upon a point without it — 

 On the figure of the earth— On the figure which the ocean would 

 assume if at rest — Index to some of the symbols which are used. 



XXXIX. Proceedings of Learned Societies. 



KOYAL SOCIETY. 

 Dec. 12. — A N account of some experiments made in the West 

 1833. IX. Indies and North America, to determine the re- 

 lative Magnetic Forces, in the years 1831, 32, and 33. By the Rev. 

 George Fisher, M.A., F.R.S. 



The experiments of which the results are given in this paper were 

 made by Mr. James Napier, late Master of H. M. S. Winchester. 

 The needles were precisely similar to those used in the experiments 

 described by the author in a former paper; and the observations were 

 made with great care, and repeated several times at the same places ; 

 by which it appeared that the intensities of the needles continued 

 unchanged during the whole period of the experiments ; and the 

 mean of all those made at one place was taken as the result. From 

 these the relative forces at different places were computed, and stated 

 in the form of a table. 



Reports were read from Sir John Herschel, Professor Airy and 

 Captain Smyth, on the performance of the refracting telescope, con- 

 structed with fluid lenses, on the plan proposed by Mr. Barlow. 



" On the Theory of the Moon." By John William Lubbock, Esq., 

 V.P. and Treas. R'S. 



M. Poisson, in a memoir which he has lately published on theTheory 

 of the Moon, expresses the three coordinates of her path, namely, 

 her true longitude, her distances, and her true latitude, in terms of 

 the time. The author observes that the reasons for so doing adduced 

 bv M. Poisson, are the same as those which led Mr. Lubbock also to 



