SECTIONAL TRANSACTIONS.— E. 343 



Mr. G. T. McCaw. — The African Arc of Meridian. 



At the last meeting of the British Association in South Africa Sir David Gill 

 gave an account of the initiation and progress of the Geodetic Survey of the sub- 

 continent. Some considerable time before 1905 he had not only visualised the 

 measurement of an Arc of Meridian through the whole of Africa, and even beyond it, 

 but had succeeded in ensuring its commencement as an extension of the Geodetic 

 Survey of the Union. Since the British Association, during this year, has brought 

 to the notice of the Home Government the desirability of completing this Arc, it is 

 not unfitting that it should be discussed at the coming South African meeting. 



After the Geodetic Survey of Southern Rhodesia had been completed by Mr. 

 A. Simms, the connection with the Transvaal was made by Capt. (now Major-General) 

 H. W. Gordon, R.E. Almost simultaneously Dr. Rubin carried the Arc northwards 

 through North-eastern Rhodesia ; but by reason of various difficulties it did not 

 reach the terminal on Lake Tanganyika projected by Mr. Cecil Rhodes — one of the 

 last decisions of that great administrator. Thus in 1906 the survey stopped short 

 of 10° S., whence to LTganda there is a gap of 9-|° of latitude. 



Following on a resolution of the old International Geodetic Association, German 

 geodesists proposed to carry the Arc through Tanganyika territory ; but the heavy 

 estimate put before the German Colonial Authorities by Helmert was considered as 

 exacting too great a burden on the then meagre resources of the colony. 



In 1905 a dispute had arisen on the Uganda-Congo frontier, involving 6,000 square 

 miles of territory. When the work of the Commission sent forthwith to map this 

 large area was approaching completion. Sir D. Gill asked the Colonial Office to carry 

 the Arc through the belt mapped by the Boundary Commission, part of the expense 

 to be borne by the scientific societies. Thus 2° of latitude were measured in Uganda 

 under the direction of the present chairman of Section E, £1,600 having been contri- 

 buted by the British Association, the Royal Society and the Royal Geographical and 

 Astronomical Societies. 



The longest portion of the Arc still to be measured is that through the Sudan, 

 with a small part in Uganda. From the southern end of Lake Albert to Wady Haifa 

 this stretch extends to about 21° in all. It is likely to involve some special difficulties, 

 for the Sudd region of the Nile lies on the way, and this area will have to be circum- 

 vented. 



From Luxor northwards to Cairo the measurement, initiated bj- Col. (now Sir 

 Henry) Lyons, F.R.S., was completed by the survey of Egypt. 



These brief notes give the outline, history and present position of the Arc of the 

 Thirtieth Meridian in Africa. Where the work has been completed it already forms 

 the ruling framework of all local surveys. In the Sudan, particularly, the need for 

 such a framework is now clamant, and in Tanganyika the sooner it can be undertaken 

 the less will be the expense to the mandated territorj', where the surve3's hitherto 

 executed are generally isolated and of very variable quality. Uganda is pursuing 

 a policy of active development of its control surveys, but in Northern Rhodesia 

 progress in this direction has been slight. 



Though there is this long reach between Rhodesia and Uganda, there is never- 

 theless a chain of secondary triangulation connecting the two portions of the Arc. 

 This chain, in part Belgian, has given a very satisfactory close in longitude ; in latitude 

 and azimuth the discordances are rather large. They have been adjusted in pro- 

 visional fashion by the joint co-operation of Commandant Maury, of the Belgian 

 Ministry of the Colonies and the Geographical Section of the General Staff. This 

 question of adjustment has already assumed importance, particularly in the connec- 

 tion between the Transvaal and Rhodesia. This and other adjustments will be 

 discussed in the paper, to which the present abstract may serve as an introduction. 



Mr. W. Whittingdale. — Map-making in South Africa. 



Mr. H. G. FouRCADE. — A New Method of Aerial Surveying. 



In two previous papers on the same subject the use of inclined plates was alone 

 considered, because it seemed that such plates being better conditioned, there was no 

 need to develop the particular case of plates exposed in an approximately horizontal 

 position. A number of other considerations which are discussed make it, however, 

 desirable to do so. 



