150 Royal Astronomical Society, 



mers have each their peculiar interest ; and some little account of 

 this arduous and toilsome undertaking will doubtless be interesting 

 to the Society. 



With the aid of his assistants and a military' detachment placed 

 under his command, Mr. Maclear began, on the 1st of September, 

 1840, the measurement of a base line, eight miles in length, on the 

 plains of Zwartland. Its direction is about west by south to east 

 by north. The measurement of the first 1600 feet was repeated, 

 and the difference of the results was found to be inappreciable, 

 though the operation was rendered most harassing by the excessive 

 heat. The measurement of the whole line occupied six months, not 

 more than from 500 to 750 feet being completed in one day. Mr. 

 Maclear thinks that there is just ground for believing that the 

 entire base, 42,818 feet in length, is scarcely erroneous to the 

 amount of half an inch, and that the error is probably much less 

 than this. 



Thenceforward the trigonometrical survey continued to occupy a 

 large share of Mr. Maclear's attention. In December 1842 he pro- 

 ceeded in H.M.S. Arrow to take the zenith sector up to the Oli- 

 phant's River, which was then intended to be the northern limit of 

 the arc, though it was afterwards deemed advisable to extend the 

 triangulation both north and south of Lacaille's original arc ; north- 

 ward to Lily Fontein on the Kamies Berg, which has been accom- 

 plished ; and southward to Cape I'Agulhas, which is approaching to 

 completion. 



This labour has subjected the observers to the greatest privations, 

 to intense heat on the arid Karroos in summer, and to extreme cold 

 in the winter, when they had to ascend such commanding heights as 

 the Cedar Berg, the Snew Cop, the Winter Hock, and the Worcester 

 Range, leaving their wagon or horses far below them, and being 

 consequently reduced to sleep under the open sky, amidst snow and 

 sleet, waiting from day to day, till the weather would admit of flash- 

 ing their heliotropes towards the concerted points. Mr. Maclear 

 speaks in the highest terms of the zeal of his assistants during the 

 whole of these laborious and trying operations. 



The East India Company has lately presented the Society with 

 two valuable volumes, printed by the order of the Madras govern- 

 ment. The first, containing the meteorological observations made 

 at the Madras Observatory for twenty years (1822-1843), will find 

 those who can more appropriately discuss its merits than your Coun- 

 cil; The second touches us more nearly. It is a Catalogue of 

 11,015 stars, made from the five volumes of Madras Observations, 

 and includes all of the Astronomical Society's Catalogue and of 

 Piazzi's, which are visible at Madras, together with 3445 southern 

 stars, selected with reference to the Paramatta Catalogue, all reduced 

 to January 1, 1835, about the middle period of the observations. 

 A systematic error of considerable magnitude in the divisions of the 

 mural circle was discovered in 1840, and its amount ascertained for 

 each single division ; and every place has been corrected for the error 

 incident to the division in which it was observed. The proper mo- 



