20 



Capt. H. G. Lyons. 



[June 6, 



These appear to show abnormally high values at Qena where the 

 faulting of the Nile Valley is highly developed, and also at Esna and 

 at Akshi (Serra) between Abu Simbel and Wadi Haifa. At this place, 

 too, the horizontal force has a high value. 



Appendix. 



Observations on the Upper Nile. 



The following observations were taken in March and April of the 

 present year (1901) while accompanying Sir W. E. Garstin, K.C.M.G., 

 Under-Secretary of State for Public Works, from Khartum through 

 the region of the " Sadcl " to Gondokoro and back, and are added 

 here with his permission. As this journey was specially undertaken to 

 see the upper reaches of the Bahr el Jebel, and to measure the 

 discharge of the White Nile and its various tributaries in this district, 

 magnetic observations had to be taken whenever opportunities 

 occurred. It has consequently happened that the stations occupied 

 cannot be described with sufficient accuracy for them to be re-occupied 

 at a future date, since most of them were wooding-stations with no 

 permanent building or other marks in the neighbourhood. 



The latitudes given are taken from the map of the Bahr el Abiad (White 

 Nile) made under the direction of General Gordon, when Governor- 

 General of the Sudan, for the stations on that river ; and those on the 

 Bahr el Jebel from a compass survey of the river made on this occa- 

 sion and adjusted to the latitudes of Gaba Shamba, Kenisa, Bor, Lado, 

 and Gondokoro, which have been determined by observations at 

 various times. (See map, p. 24.) 



The station occupied at Omclurman was on the left bank of the Nile, 

 half-way between the gunboat workshops and the angle of the old 

 Omdurman wall, and about 100 metres from the river bank. 



These observations, extending as they do from about 16° to 5° 

 north latitude, and crossing the magnetic equator, form an interesting 

 continuation to those from Cairo to Wadi Haifa, 30° N. to 21° 30' N., 

 which have been given above. 



No attempt has been made to reduce these southern results to the 

 same epoch as the others, since no reliable data are as yet available for 

 doing so. Hardly any observations exist, it seems, which can be 

 utilised to determine the secular change. Pruysenaere's results (quoted 

 in the following short table taken from ' Petermann's Mittheilungen,' 

 Erganz.-heft 51, 1877) in the desert east of the Bahr el Abyad (White 

 Nile) appear to show too much local attraction to be of much use. 



An observation of Russegger's in April, 1837, at Torra, on the Bahr 

 el Abyad, gives 9° W. for the declination, which, taking the present 

 value at 5° 20' W., gives 3° 4' of annual decrease. 



