VerificatioJi 0/ Lacaille's Arc qf the Meridian. 593 



law of accelerating force and retarding friction. The result is, that 

 the effect of these forces is to increase continually the inequality 

 of motion. 



Note on an Arabic Globe belonging to the Society. By R. W. 

 Rothman, Esq. M.A., Foreign Secretary. 



The instrument in question is a small bronze globe, about six 

 inches in diameter, brought some time ago from the East, having 

 the positions of the principal stars marked by silver studs, with 

 their Arabic names engraved ; and the object of the present note is 

 to point out the diiferences between the names of the stars as found 

 on the globe, and those given in the Catalogue of Ulugh Beg, with 

 which, in general, the globe agrees, though in some instances the 

 differences are worthy of notice. From the position of the colour, 

 &c. it is inferred that the globe is not of ancient date ; but it bears 

 no mark indicative of the precise period of its construction. 



Elements of Galle's Second Comet ; computed by M. Petersen, 

 and communicated by Professor Schumacher. 



April 10. — The following communications were read : — 



Observations made at the Cape of Good Hope, in the year 1838, 

 with Bradley's Zenith Sector, for the Verification of the Abbe De 

 Lacaille's Arc of the Meridian. By Thomas Maclear, Esq. F.R.S. 

 Communicated by the Lords Commissioners of the Admiralty*. 



The present paper is the second which has been received from 

 Mr. Maclear on the subject of the important and interesting opera- 

 tions now going on at the Cape, relative to the measurement of an 

 arc of the meridian. 



In the former communication, an account of which is given in the 

 Monthly Notice for April 1839 (Phil. Mag. Third Series, vol. xiv. 

 p. 522), Mr. Maclear detailed his proceedings for the purpose of 

 identifying the terminal station of Lacaille's arc ; the present con- 

 tains the sector observations, with their reduction, and the deter- 

 mination of the amplitude of the arc. 



The sector was delivered to Mr. Maclear in Table Bay, by Cap- 

 tain Maitland, of H. M. ship Wellesley, on the 9th of December, 

 1837, and was conveyed the same day to the Royal Observatory 

 under his personal superintendence ; and on the 10th the instru- 

 ment was put together and erected in the centre room. As this 

 room was originally constructed for a zenith-tube of limited dimen- 

 sions, it became necessary to enlarge the apertures by sawing 

 through a portion of the iron bars of the grating forming the floor 

 of the lantern, and of the rafters above. In this tedious operation 

 nearly a month was consumed ; but, in the meanwhile, a tent and 

 a tripod for the support of the sector were prepared, a list of stars 

 selected, and a variety of details settled, in which the author states 

 Sir J. Ilerschel cordially assisted with his advice. 



The site of Lacaille's Observatory in Cape Town being covered 

 by a large building, erected since 1752, the sector could not be 

 placed exactly over Lacaille's station ; it was accordingly raised in 

 the court-yard of the house, under a tent, and every disposition 



* [See Phil. Mag. Third Series, vol. xvi. p. 594.] 

 Fhil. May. S. 3. Vol. 18. No. 120. Hupjtl. July 1841. 2 Q 



